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"Y'all are funny! 73, Ray AA4EZ"
I'm getting an immense kick out of this thread, as NVIS is not a frequency, OR antenna, but a method of propagation, regardless of how it's created. Horizontal, vertical, circular, NVIS in varying modes... Suddenly it became something special.
It can also be controlled, from coming nearly right back down on top of one, to fall within the "skip zone", or directed out to where it's less "NVIS", and more typical "skip", conditions permitting, with everything in between. Nobody puts Az/El rotators on their HF arrays any more...
Add to this that a fixed "low antenna" is in fact irrelevant (note all the height discrepancies, really big clue!), as what makes the mode occur is a completely random variable between the surface on walks on, or the antenna is mounted over, to the core of the planet, and all the stories, and theories, with little to no understanding at best, just gets super silly.
A "NVIS" antenna can actually be created to work independently, relative unto itself, regardless of surroundings, from on Earth, to free space, but funny nobody does that... You'd think that part would be super important.
I'm waiting for the "works from X to X MHz only' comments based on some really bad stories of wildly limited equipment from decades ago, despite:
Scattering and NVIS of electromagnetic waves has been known to occur up to ~650 THz (TeraHertz) since the 1860's, the National Weather Service and DOE demonstrated it to ~263 MHz in the early 1960's when trying to determine if it was consistent enough to use during the Cold War (but they stopped at the lower edge of a gap, whoops, shoulda checked again, higher, to at least know as much as they could and let the rest of the world know), I've demonstrated it at 545THz, and for the past year and a half, have been trying to demonstrate it at ~750Thz, but conditions have only existed in the region twice, both of which I missed (you thought 6m was unstable!), and, 750THz is frighteningly dangerous at 15W. So, I've really got some mixed feelings about proving it, so the world can thoroughly suck it, again, and getting hurt.
I wouldn't feel bad, really, the NVIS forums have been wavering around 0-1 on knowledge of the matter since their inception.
Kurt
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Raymond Lewis
I think a lot of y'all need to look up Randy of GMRS fame and his YouTube channel (I think it is called notarubecon). He has a term he uses called "SAD HAMS" and see how many people fall into his definition. Y'all are funny! 73, Ray AA4EZ
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At the risk of driving the point further than necessary I want to say that Joe is absolutely correct if the myth he was trying to discredit was that very low antennas are required (or desirable) for NVIS communication, he is absolutely right. I never even considered that to even be a talking point, which is why I missed it. They are not. I've made too many QSO's on my vertical and quad to know that is a myth. So to summarize both my point and Joe's point, the NVIS antenna is not a myth, but that it's necessary or desirable for close in work, is a myth. Yes, as pointed out below, there may be situations where lowering the antenna is desirable and intentional.
Gene
WB7RLX
toggle quoted message
Show quoted text
-----Original Message----- From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of David Herring Sent: Sunday, September 4, 2022 10:54 AM To: main@WSJTX.groups.io Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal Joe, Thank you for clarifying what you really meant...that is much easier to follow. No quarrels with that here. To answer your question, "why handicap oneself?" well the answer is simple: in the instances where I would even bother, intentionally, with an NVIS antenna, I would only be interested in regional communications. In my specific case back then, I was participating in local nets where I only wanted comms within the state of Hawaii. I specifically did NOT want to have mainland US, Japan, Asiatic Russia, China, Australia and any number of other countries calling me. When I used a higher antenna, that happened. A lot. The lower antenna cut that out while still performing locally. Also having it lower cut out a lot of noise, making operating locally less fatiguing. I honestly cannot think of any other reason to have an NVIS antenna. Well, at least to intentionally have one. I get that sometimes hams are limited by money, physics and XYLs and can't really help it... As far as when I was not on the local nets and wanted distance, I had a vertical over there that worked like gangbusters... ;-) 73, Dave - N5DCH On 9/4/22 09:44, Joe Subich, W4TV wrote: On 2022-09-04 11:13 AM, David Herring wrote:
According to W4TV in the last paragraph of his last message, he says
in essence if one puts their dipole too low then they are losing
anywhere from 100% to 125% of their transmitted power. I dd not say or imply that one was losing 100% to 150% of transmitted
power. I said that ground losses (depending on the quality of the
ground - note: NEC2 shows "perfect ground" is lossless) are between
3 and 6 dB for antennas between 1/8 and 1/16 wave above ground.
In addition, *of the RF actually radiated* that "cone" above 50 to 75
degrees (depending on how far below the MUF one is operating) goes
straight out into space. To make the math simple, if one assume no
radiation below 15 degrees (it's actually down 12 dB with a 1/8 wave
high dipole) and operation at 50% of the MUF [F(crit) = 50% of MUF],
60 of 150 degrees of radiation is "lost" or 4 dB *of what was left*
after ground losses.
If you want to put that is terms of transmitter power: For a 1/16 wave
high dipole, 75% is lost in the ground of the remaining 25%,
1/3 goes out into space. That's a total loss of 7.8 dB or 84% of the
transmitter power.
Some months ago, I caught all kinds of heck on here when I shared
that while living on Kauai, I ran a 40 meter dipole at 15 feet above
ground and got excellent results for regional communications in a
circle of about 400 miles. Sure 16W ERP will do that. The distance losses are almost nothing at
400 miles on 7.1MHz. However, why handicap one's self? Put that
dipole up at 45 feet and pick up at least 6dB of ERP at no cost.
73,
... Joe, W4TV
On 2022-09-04 11:13 AM, David Herring wrote:
OK, I can’t remain quiet on this one…
According to W4TV in the last paragraph of his last message, he says
in essence if one puts their dipole too low then they are losing
anywhere from 100% to 125% of their transmitted power.
Losses greater than 100%? That’s a neat trick! How exactly does
that work? Heck, how do you even get 100% loss? Even a dummy load
radiates a little bit. ;-)
Some months ago, I caught all kinds of heck on here when I shared
that while living on Kauai, I ran a 40 meter dipole at 15 feet above
ground and got excellent results for regional communications in a
circle of about 400 miles. It seemed like I could not get anyone to
understand that I did not care one flying iota about losses, distance
and whatever other theoretical-backed-by-science objections they
threw at me. I had an antenna that *ACTUALLY* *WORKED* *PERFECTLY*
for what it was intended for. Flawless, gapless, consistant,
reliable, low noise 40 meter communications across the Hawaiian Islands.
I respect the math, and the simulations and the modeling and the
engineering credentials and such as that…goodness knows I’ve done
plenty of it myself. But at some point, like for example when you
think you’re getting 125% losses, we as hams need to pull our noses
out from the books and computers and go stick some wire up in the air
and try it.
And with that, I am donning my asbestos suit and making myself
scarce… ;-)
73,
Dave - N5DCH
On Sep 4, 2022, at 8:25 AM, Joe Subich, W4TV <lists@...> wrote:
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
Model any HF dipole antenna and vary it's elevation from 1/8 of a
wavelength to a full wavelength above ground and you will be able
to see how the takeoff angle varies. It's not the takeoff angle that is important. Below 1/4 wave (the
definition of an NVIS Antenna) the TOA is 90 degrees and does not
vary. The issues are that F(crit) for 90 degrees is zero and that
ground losses increase dramatically below 1/4 wave.
NEC with perfect ground will not show those losses ... even with
"high accuracy" ground NEC 2 only shows 2-3 dB of loss at 1/8 wave
(it's up to 6dB at 1/16 wave or ~20' on 80 meters) but that still
understates the true losses with poor ground (NEC4/NEC5 do a better
job of getting at the true losses).
Between ground losses below 1/8 wave, losses due to the critical
frequency, losses due to D layer absorption, low antenna NVIS is
just another myth. Now, if you want to confine the NVIS discussion
to antennas at 20' or higher on 30 meters and above, we can discuss
their utility for "close in" communications. Similarly, we can
discuss the utility of antennas as low as 30' on 40 meters or 60' on
80 meters *AT NIGHT* when the MUF is lower and D layer
thins/disappears. At lesser heights one is dumping 50 to 75% of the
transmitter power right into the dirt and radiating another 50%
right out into space.
73,
... Joe, W4TV
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
If I might clarify. NVIS Antennas are anything but a myth, and
many hams without realizing it use NVIS antennas. What most people
don't realize is that almost any horizontal dipole like antenna (a
traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end
fed wire) suspended below 1/4 wavelength above real ground is an
NVIS antenna, meaning they send most of their RF energy at high
angles (above 45 degrees) and yes much of that energy is absorbed
in the D layer or just continues on into space. Yes they are
inefficient, yes they generally do not make good DX antennas. But
they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a
wavelength to a full wavelength above ground and you will be able
to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly
inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf
Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal On
2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS
are a myth. Any horizontal antenna less than 1/4 wave above ground
suffers significant loss. Maximum radiation is straight up but the
"critical frequency" (frequency at which radiation at 90 degrees
passes through the ionosphere) is generally well below even 80
meters most of the time. Even then, the D layer absorption during
daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at
approximately 50 feet for 80/40/30 meters and 35 feet for 20-10
meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown
<k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be
using NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
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You can achieve all your goals by simply turning down the RF gain.
Raise you ant (if possible) and you can work your buds at 10 watts
instead of 100W.
Bob - wd6dod
toggle quoted message
Show quoted text
On 9/4/2022 9:53 AM, David Herring wrote: Joe,
Thank you for clarifying what you really meant...that is much easier to follow. No quarrels with that here.
To answer your question, "why handicap oneself?" well the answer is simple: in the instances where I would even bother, intentionally, with an NVIS antenna, I would only be interested in regional communications. In my specific case back then, I was participating in local nets where I only wanted comms within the state of Hawaii. I specifically did NOT want to have mainland US, Japan, Asiatic Russia, China, Australia and any number of other countries calling me. When I used a higher antenna, that happened. A lot. The lower antenna cut that out while still performing locally.
Also having it lower cut out a lot of noise, making operating locally less fatiguing.
I honestly cannot think of any other reason to have an NVIS antenna. Well, at least to intentionally have one. I get that sometimes hams are limited by money, physics and XYLs and can't really help it...
As far as when I was not on the local nets and wanted distance, I had a vertical over there that worked like gangbusters... ;-)
73,
Dave - N5DCH
On 9/4/22 09:44, Joe Subich, W4TV wrote:
On 2022-09-04 11:13 AM, David Herring wrote:
According to W4TV in the last paragraph of his last message, he says in essence if one puts their dipole too low then they are losing anywhere from 100% to 125% of their transmitted power. I dd not say or imply that one was losing 100% to 150% of transmitted
power. I said that ground losses (depending on the quality of the
ground - note: NEC2 shows "perfect ground" is lossless) are between
3 and 6 dB for antennas between 1/8 and 1/16 wave above ground.
In addition, *of the RF actually radiated* that "cone" above 50 to 75
degrees (depending on how far below the MUF one is operating) goes
straight out into space. To make the math simple, if one assume no
radiation below 15 degrees (it's actually down 12 dB with a 1/8 wave
high dipole) and operation at 50% of the MUF [F(crit) = 50% of MUF],
60 of 150 degrees of radiation is "lost" or 4 dB *of what was left*
after ground losses.
If you want to put that is terms of transmitter power: For a 1/16
wave high dipole, 75% is lost in the ground of the remaining 25%,
1/3 goes out into space. That's a total loss of 7.8 dB or 84% of
the transmitter power.
Some months ago, I caught all kinds of heck on here when I shared that while living on Kauai, I ran a 40 meter dipole at 15 feet above ground and got excellent results for regional communications in a
circle of about 400 miles. Sure 16W ERP will do that. The distance losses are almost nothing
at 400 miles on 7.1MHz. However, why handicap one's self? Put
that dipole up at 45 feet and pick up at least 6dB of ERP at no
cost.
73,
... Joe, W4TV
On 2022-09-04 11:13 AM, David Herring wrote:
OK, I can’t remain quiet on this one…
According to W4TV in the last paragraph of his last message, he says in essence if one puts their dipole too low then they are losing anywhere from 100% to 125% of their transmitted power.
Losses greater than 100%? That’s a neat trick! How exactly does that work? Heck, how do you even get 100% loss? Even a dummy load radiates a little bit. ;-)
Some months ago, I caught all kinds of heck on here when I shared that while living on Kauai, I ran a 40 meter dipole at 15 feet above ground and got excellent results for regional communications in a circle of about 400 miles. It seemed like I could not get anyone to understand that I did not care one flying iota about losses, distance and whatever other theoretical-backed-by-science objections they threw at me. I had an antenna that *ACTUALLY* *WORKED* *PERFECTLY* for what it was intended for. Flawless, gapless, consistant, reliable, low noise 40 meter communications across the Hawaiian Islands.
I respect the math, and the simulations and the modeling and the engineering credentials and such as that…goodness knows I’ve done plenty of it myself. But at some point, like for example when you think you’re getting 125% losses, we as hams need to pull our noses out from the books and computers and go stick some wire up in the air and try it.
And with that, I am donning my asbestos suit and making myself scarce… ;-)
73,
Dave - N5DCH
On Sep 4, 2022, at 8:25 AM, Joe Subich, W4TV <lists@...> wrote:
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to
see how the takeoff angle varies. It's not the takeoff angle that is important. Below 1/4 wave (the
definition of an NVIS Antenna) the TOA is 90 degrees and does not
vary. The issues are that F(crit) for 90 degrees is zero and that
ground losses increase dramatically below 1/4 wave.
NEC with perfect ground will not show those losses ... even with
"high accuracy" ground NEC 2 only shows 2-3 dB of loss at 1/8 wave
(it's up to 6dB at 1/16 wave or ~20' on 80 meters) but that still
understates the true losses with poor ground (NEC4/NEC5 do a better
job of getting at the true losses).
Between ground losses below 1/8 wave, losses due to the critical
frequency, losses due to D layer absorption, low antenna NVIS is
just another myth. Now, if you want to confine the NVIS discussion
to antennas at 20' or higher on 30 meters and above, we can discuss
their utility for "close in" communications. Similarly, we can
discuss the utility of antennas as low as 30' on 40 meters or
60' on 80 meters *AT NIGHT* when the MUF is lower and D layer
thins/disappears. At lesser heights one is dumping 50 to 75%
of the transmitter power right into the dirt and radiating another
50% right out into space.
73,
... Joe, W4TV
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
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Joe,
Thank you for clarifying what you really meant...that is much easier to follow. No quarrels with that here.
To answer your question, "why handicap oneself?" well the answer is simple: in the instances where I would even bother, intentionally, with an NVIS antenna, I would only be interested in regional communications. In my specific case back then, I was participating in local nets where I only wanted comms within the state of Hawaii. I specifically did NOT want to have mainland US, Japan, Asiatic Russia, China, Australia and any number of other countries calling me. When I used a higher antenna, that happened. A lot. The lower antenna cut that out while still performing locally.
Also having it lower cut out a lot of noise, making operating locally less fatiguing.
I honestly cannot think of any other reason to have an NVIS antenna. Well, at least to intentionally have one. I get that sometimes hams are limited by money, physics and XYLs and can't really help it...
As far as when I was not on the local nets and wanted distance, I had a vertical over there that worked like gangbusters... ;-)
73,
Dave - N5DCH
toggle quoted message
Show quoted text
On 9/4/22 09:44, Joe Subich, W4TV wrote: On 2022-09-04 11:13 AM, David Herring wrote:
According to W4TV in the last paragraph of his last message, he says in essence if one puts their dipole too low then they are losing anywhere from 100% to 125% of their transmitted power. I dd not say or imply that one was losing 100% to 150% of transmitted
power. I said that ground losses (depending on the quality of the
ground - note: NEC2 shows "perfect ground" is lossless) are between
3 and 6 dB for antennas between 1/8 and 1/16 wave above ground.
In addition, *of the RF actually radiated* that "cone" above 50 to 75
degrees (depending on how far below the MUF one is operating) goes
straight out into space. To make the math simple, if one assume no
radiation below 15 degrees (it's actually down 12 dB with a 1/8 wave
high dipole) and operation at 50% of the MUF [F(crit) = 50% of MUF],
60 of 150 degrees of radiation is "lost" or 4 dB *of what was left*
after ground losses.
If you want to put that is terms of transmitter power: For a 1/16
wave high dipole, 75% is lost in the ground of the remaining 25%,
1/3 goes out into space. That's a total loss of 7.8 dB or 84% of
the transmitter power.
Some months ago, I caught all kinds of heck on here when I shared that while living on Kauai, I ran a 40 meter dipole at 15 feet above ground and got excellent results for regional communications in a
circle of about 400 miles. Sure 16W ERP will do that. The distance losses are almost nothing
at 400 miles on 7.1MHz. However, why handicap one's self? Put
that dipole up at 45 feet and pick up at least 6dB of ERP at no
cost.
73,
... Joe, W4TV
On 2022-09-04 11:13 AM, David Herring wrote:
OK, I can’t remain quiet on this one…
According to W4TV in the last paragraph of his last message, he says in essence if one puts their dipole too low then they are losing anywhere from 100% to 125% of their transmitted power.
Losses greater than 100%? That’s a neat trick! How exactly does that work? Heck, how do you even get 100% loss? Even a dummy load radiates a little bit. ;-)
Some months ago, I caught all kinds of heck on here when I shared that while living on Kauai, I ran a 40 meter dipole at 15 feet above ground and got excellent results for regional communications in a circle of about 400 miles. It seemed like I could not get anyone to understand that I did not care one flying iota about losses, distance and whatever other theoretical-backed-by-science objections they threw at me. I had an antenna that *ACTUALLY* *WORKED* *PERFECTLY* for what it was intended for. Flawless, gapless, consistant, reliable, low noise 40 meter communications across the Hawaiian Islands.
I respect the math, and the simulations and the modeling and the engineering credentials and such as that…goodness knows I’ve done plenty of it myself. But at some point, like for example when you think you’re getting 125% losses, we as hams need to pull our noses out from the books and computers and go stick some wire up in the air and try it.
And with that, I am donning my asbestos suit and making myself scarce… ;-)
73,
Dave - N5DCH
On Sep 4, 2022, at 8:25 AM, Joe Subich, W4TV <lists@...> wrote:
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to
see how the takeoff angle varies. It's not the takeoff angle that is important. Below 1/4 wave (the
definition of an NVIS Antenna) the TOA is 90 degrees and does not
vary. The issues are that F(crit) for 90 degrees is zero and that
ground losses increase dramatically below 1/4 wave.
NEC with perfect ground will not show those losses ... even with
"high accuracy" ground NEC 2 only shows 2-3 dB of loss at 1/8 wave
(it's up to 6dB at 1/16 wave or ~20' on 80 meters) but that still
understates the true losses with poor ground (NEC4/NEC5 do a better
job of getting at the true losses).
Between ground losses below 1/8 wave, losses due to the critical
frequency, losses due to D layer absorption, low antenna NVIS is
just another myth. Now, if you want to confine the NVIS discussion
to antennas at 20' or higher on 30 meters and above, we can discuss
their utility for "close in" communications. Similarly, we can
discuss the utility of antennas as low as 30' on 40 meters or
60' on 80 meters *AT NIGHT* when the MUF is lower and D layer
thins/disappears. At lesser heights one is dumping 50 to 75%
of the transmitter power right into the dirt and radiating another
50% right out into space.
73,
... Joe, W4TV
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
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4U1UN was on 30 meters FT8 early this morning at 09:23z with a good signal into upstate NY.
I have him on 40 meters SSB/FT8, 30 meters CW/FT8 and 20 meters FT8 with a Hustler 6BTV ground mounted vertical. It just takes a little patience.
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On 2022-09-04 11:16 AM, Larry Banks via groups.io wrote: We tend to forget that, IIRC, "NVIS" antennas had their origin with
the Army -- who can run gobs of power. Plus, the "NV" of NVIS is
"Near Vertical," not vertical. *AND* the old standard MS-44 mast (antenna) set was *40 feet tall*. 73, ... Joe, W4TV On 2022-09-04 11:16 AM, Larry Banks via groups.io wrote: We tend to forget that, IIRC, "NVIS" antennas had their origin with the Army -- who can run gobs of power. Plus, the "NV" of NVIS is "Near Vertical," not vertical.
Larry / W1DYJ
On 9/4/2022 10:25, Joe Subich, W4TV wrote:
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to
see how the takeoff angle varies. It's not the takeoff angle that is important. Below 1/4 wave (the
definition of an NVIS Antenna) the TOA is 90 degrees and does not
vary. The issues are that F(crit) for 90 degrees is zero and that
ground losses increase dramatically below 1/4 wave.
NEC with perfect ground will not show those losses ... even with
"high accuracy" ground NEC 2 only shows 2-3 dB of loss at 1/8 wave
(it's up to 6dB at 1/16 wave or ~20' on 80 meters) but that still
understates the true losses with poor ground (NEC4/NEC5 do a better
job of getting at the true losses).
Between ground losses below 1/8 wave, losses due to the critical
frequency, losses due to D layer absorption, low antenna NVIS is
just another myth. Now, if you want to confine the NVIS discussion
to antennas at 20' or higher on 30 meters and above, we can discuss
their utility for "close in" communications. Similarly, we can
discuss the utility of antennas as low as 30' on 40 meters or
60' on 80 meters *AT NIGHT* when the MUF is lower and D layer
thins/disappears. At lesser heights one is dumping 50 to 75%
of the transmitter power right into the dirt and radiating another
50% right out into space.
73,
... Joe, W4TV
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
|
|
|
On 2022-09-04 11:13 AM, David Herring wrote: According to W4TV in the last paragraph of his last message, he says in essence if one puts their dipole too low then they are losing anywhere from 100% to 125% of their transmitted power. I dd not say or imply that one was losing 100% to 150% of transmitted power. I said that ground losses (depending on the quality of the ground - note: NEC2 shows "perfect ground" is lossless) are between 3 and 6 dB for antennas between 1/8 and 1/16 wave above ground. In addition, *of the RF actually radiated* that "cone" above 50 to 75 degrees (depending on how far below the MUF one is operating) goes straight out into space. To make the math simple, if one assume no radiation below 15 degrees (it's actually down 12 dB with a 1/8 wave high dipole) and operation at 50% of the MUF [F(crit) = 50% of MUF], 60 of 150 degrees of radiation is "lost" or 4 dB *of what was left* after ground losses. If you want to put that is terms of transmitter power: For a 1/16 wave high dipole, 75% is lost in the ground of the remaining 25%, 1/3 goes out into space. That's a total loss of 7.8 dB or 84% of the transmitter power. Some months ago, I caught all kinds of heck on here when I shared that while living on Kauai, I ran a 40 meter dipole at 15 feet above ground and got excellent results for regional communications in a
circle of about 400 miles. Sure 16W ERP will do that. The distance losses are almost nothing at 400 miles on 7.1MHz. However, why handicap one's self? Put that dipole up at 45 feet and pick up at least 6dB of ERP at no cost. 73, ... Joe, W4TV On 2022-09-04 11:13 AM, David Herring wrote: OK, I can’t remain quiet on this one…
According to W4TV in the last paragraph of his last message, he says in essence if one puts their dipole too low then they are losing anywhere from 100% to 125% of their transmitted power.
Losses greater than 100%? That’s a neat trick! How exactly does that work? Heck, how do you even get 100% loss? Even a dummy load radiates a little bit. ;-)
Some months ago, I caught all kinds of heck on here when I shared that while living on Kauai, I ran a 40 meter dipole at 15 feet above ground and got excellent results for regional communications in a circle of about 400 miles. It seemed like I could not get anyone to understand that I did not care one flying iota about losses, distance and whatever other theoretical-backed-by-science objections they threw at me. I had an antenna that *ACTUALLY* *WORKED* *PERFECTLY* for what it was intended for. Flawless, gapless, consistant, reliable, low noise 40 meter communications across the Hawaiian Islands.
I respect the math, and the simulations and the modeling and the engineering credentials and such as that…goodness knows I’ve done plenty of it myself. But at some point, like for example when you think you’re getting 125% losses, we as hams need to pull our noses out from the books and computers and go stick some wire up in the air and try it.
And with that, I am donning my asbestos suit and making myself scarce… ;-)
73,
Dave - N5DCH
On Sep 4, 2022, at 8:25 AM, Joe Subich, W4TV <lists@...> wrote:
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to
see how the takeoff angle varies. It's not the takeoff angle that is important. Below 1/4 wave (the
definition of an NVIS Antenna) the TOA is 90 degrees and does not
vary. The issues are that F(crit) for 90 degrees is zero and that
ground losses increase dramatically below 1/4 wave.
NEC with perfect ground will not show those losses ... even with
"high accuracy" ground NEC 2 only shows 2-3 dB of loss at 1/8 wave
(it's up to 6dB at 1/16 wave or ~20' on 80 meters) but that still
understates the true losses with poor ground (NEC4/NEC5 do a better
job of getting at the true losses).
Between ground losses below 1/8 wave, losses due to the critical
frequency, losses due to D layer absorption, low antenna NVIS is
just another myth. Now, if you want to confine the NVIS discussion
to antennas at 20' or higher on 30 meters and above, we can discuss
their utility for "close in" communications. Similarly, we can
discuss the utility of antennas as low as 30' on 40 meters or
60' on 80 meters *AT NIGHT* when the MUF is lower and D layer
thins/disappears. At lesser heights one is dumping 50 to 75%
of the transmitter power right into the dirt and radiating another
50% right out into space.
73,
... Joe, W4TV
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
|
|
|
On 2022-09-03 11:28 PM, Michael Black via groups.io wrote: >> Joe...can you explain then why an ionosonde works at all? It's getting reflections from other than directly over head.
"Normal" is 90 degrees ... COS(90)= 0. The ionosonde report shows "direction to the ionospheric returns" ... there would be no >"direction" for a return from directly overhead. Hi Joe, Unfortunately you are using a wrong angle definition. Yours is the elevation angle, but the critical frequency to MUF equation is using incidence angle that is 90 - elevation angle. That of course "inverts" all calculation giving maximum reflection at your 90 degrees angle. The direction in the ionosondes indicate the direction of the reflection for certain propagation modes. The main ones do reflect at vertical direction so called ordinary and extraordinary wave having mainly opposite circular polarizations. You may study it e.g. in: http://digisonde.com/pdf/Digisonde4DManual_LDI-web.pdf. Figure 1-23 shows the synthetic reception antenna. http://digisonde.com/digisonde.html contains a picture called Skymap that clearly shows how the signal arrival is around vertical, mainly within 30 degrees and maximum at your 90 degrees i.e. vertical. Ionogram picture especially shows the vertical-incidence normal ionograms. 73, Reino OH3mA
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Larry Banks
We tend to forget that, IIRC, "NVIS" antennas had their origin with the Army -- who can run gobs of power. Plus, the "NV" of NVIS is "Near Vertical," not vertical.
Larry / W1DYJ
toggle quoted message
Show quoted text
On 9/4/2022 10:25, Joe Subich, W4TV wrote: On 2022-09-03 7:23 PM, Eugene Morgan wrote:
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to
see how the takeoff angle varies. It's not the takeoff angle that is important. Below 1/4 wave (the
definition of an NVIS Antenna) the TOA is 90 degrees and does not
vary. The issues are that F(crit) for 90 degrees is zero and that
ground losses increase dramatically below 1/4 wave.
NEC with perfect ground will not show those losses ... even with
"high accuracy" ground NEC 2 only shows 2-3 dB of loss at 1/8 wave
(it's up to 6dB at 1/16 wave or ~20' on 80 meters) but that still
understates the true losses with poor ground (NEC4/NEC5 do a better
job of getting at the true losses).
Between ground losses below 1/8 wave, losses due to the critical
frequency, losses due to D layer absorption, low antenna NVIS is
just another myth. Now, if you want to confine the NVIS discussion
to antennas at 20' or higher on 30 meters and above, we can discuss
their utility for "close in" communications. Similarly, we can
discuss the utility of antennas as low as 30' on 40 meters or
60' on 80 meters *AT NIGHT* when the MUF is lower and D layer
thins/disappears. At lesser heights one is dumping 50 to 75%
of the transmitter power right into the dirt and radiating another
50% right out into space.
73,
... Joe, W4TV
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
|
|
|
OK, I can’t remain quiet on this one…
According to W4TV in the last paragraph of his last message, he says in essence if one puts their dipole too low then they are losing anywhere from 100% to 125% of their transmitted power.
Losses greater than 100%? That’s a neat trick! How exactly does that work? Heck, how do you even get 100% loss? Even a dummy load radiates a little bit. ;-)
Some months ago, I caught all kinds of heck on here when I shared that while living on Kauai, I ran a 40 meter dipole at 15 feet above ground and got excellent results for regional communications in a circle of about 400 miles. It seemed like I could not get anyone to understand that I did not care one flying iota about losses, distance and whatever other theoretical-backed-by-science objections they threw at me. I had an antenna that *ACTUALLY* *WORKED* *PERFECTLY* for what it was intended for. Flawless, gapless, consistant, reliable, low noise 40 meter communications across the Hawaiian Islands.
I respect the math, and the simulations and the modeling and the engineering credentials and such as that…goodness knows I’ve done plenty of it myself. But at some point, like for example when you think you’re getting 125% losses, we as hams need to pull our noses out from the books and computers and go stick some wire up in the air and try it.
And with that, I am donning my asbestos suit and making myself scarce… ;-)
73,
Dave - N5DCH
toggle quoted message
Show quoted text
On Sep 4, 2022, at 8:25 AM, Joe Subich, W4TV <lists@...> wrote:
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to
see how the takeoff angle varies. It's not the takeoff angle that is important. Below 1/4 wave (the
definition of an NVIS Antenna) the TOA is 90 degrees and does not
vary. The issues are that F(crit) for 90 degrees is zero and that
ground losses increase dramatically below 1/4 wave.
NEC with perfect ground will not show those losses ... even with
"high accuracy" ground NEC 2 only shows 2-3 dB of loss at 1/8 wave
(it's up to 6dB at 1/16 wave or ~20' on 80 meters) but that still
understates the true losses with poor ground (NEC4/NEC5 do a better
job of getting at the true losses).
Between ground losses below 1/8 wave, losses due to the critical
frequency, losses due to D layer absorption, low antenna NVIS is
just another myth. Now, if you want to confine the NVIS discussion
to antennas at 20' or higher on 30 meters and above, we can discuss
their utility for "close in" communications. Similarly, we can
discuss the utility of antennas as low as 30' on 40 meters or
60' on 80 meters *AT NIGHT* when the MUF is lower and D layer
thins/disappears. At lesser heights one is dumping 50 to 75%
of the transmitter power right into the dirt and radiating another
50% right out into space.
73,
... Joe, W4TV
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
|
|
|
On 2022-09-03 7:23 PM, Eugene Morgan wrote: Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to
see how the takeoff angle varies. It's not the takeoff angle that is important. Below 1/4 wave (the definition of an NVIS Antenna) the TOA is 90 degrees and does not vary. The issues are that F(crit) for 90 degrees is zero and that ground losses increase dramatically below 1/4 wave. NEC with perfect ground will not show those losses ... even with "high accuracy" ground NEC 2 only shows 2-3 dB of loss at 1/8 wave (it's up to 6dB at 1/16 wave or ~20' on 80 meters) but that still understates the true losses with poor ground (NEC4/NEC5 do a better job of getting at the true losses). Between ground losses below 1/8 wave, losses due to the critical frequency, losses due to D layer absorption, low antenna NVIS is just another myth. Now, if you want to confine the NVIS discussion to antennas at 20' or higher on 30 meters and above, we can discuss their utility for "close in" communications. Similarly, we can discuss the utility of antennas as low as 30' on 40 meters or 60' on 80 meters *AT NIGHT* when the MUF is lower and D layer thins/disappears. At lesser heights one is dumping 50 to 75% of the transmitter power right into the dirt and radiating another 50% right out into space. 73, ... Joe, W4TV On 2022-09-03 7:23 PM, Eugene Morgan wrote: If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
|
|
|
On 2022-09-03 11:28 PM, Michael Black via groups.io wrote: Joe...can you explain then why an ionosonde works at all? It's getting reflections from other than directly over head. "Normal" is 90 degrees ... COS(90)= 0. The ionosonde report shows "direction to the ionospheric returns" ... there would be no "direction" for a return from directly overhead. 73, ... Joe, W4TV On 2022-09-03 11:28 PM, Michael Black via groups.io wrote: Joe...can you explain then why an ionosonde works at all? If reflection is actually COS(@) seems they wouldn't work at all.https://en.wikipedia.org/wiki/Ionosonde
Mike W9MDB
On Saturday, September 3, 2022 at 07:16:25 PM CDT, Joe Subich, W4TV <lists@...> wrote:
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
If I might clarify. NVIS Antennas are anything but a myth, and many > hams without realizing it use NVIS antennas.
The "special properties" of NVIS antennas are a myth.
Radiation at 90 degrees (straight up) from a horizontal dipole increases
to a maximum at 1/4 wave above ground. However, the critical frequency
(frequency at which RF passes through the ionosphere) is F(muf)*COS(@)
where @ is the angle of incidence. For a 90 degree angle of incidence,
F(crit) is *0 Hz* - IOW, 90 degree RF is not reflected *AT ALL* and RF
close to 90 degrees is only reflected under rare conditions. At 60
degrees, the critical frequency is half the MUF ...IOW for NVIS at 20
meters the MUF needs to be above 10 meters for even 60 degree radiation!
One is far better served to get the antenna above 0.32 wave high
getting the peak lobe *DOWN* below 50 degrees where it will do
some good.
73,
... Joe, W4TV
On 2022-09-03 7:23 PM, Eugene Morgan wrote:
If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
|
|
|
Exactly, that's in part why I said they are inefficient. And I've read the material and a lot more as well and modeled and built more than I care to remember. If you have to resort to citing your credential as a way to win an disagreement then it's time to terminate this QSO, there nothing constructive that can come of it at this point. An NVIS antenna is a dipole that is generally less than 1/4 wavelength the ground. It radiates good portion of its energy above 45 degrees. And yes because they are so low to the ground a lot of that energy is wasted. How many times do I need to say they are inefficient?
At 60' an 80 meter dipole is no longer consider an NVIS antenna based on my understanding of what an NVIS antenna is. Ditto a 40 meter at 30' or more, and so on.
Take off angle is a flowed concept? Wow..... If that's what you think then there's very little point in carrying this conversation any further. I rely on low take off angles for working DX which is why I use a Quad and a vertical as my mainstay antennas.
I'm going to QRT at this point. We have beat this horse to death and if all you have are credentials to try and impress me with then I think we are pretty much done at this point.
73,
Gene
WB7RLX
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-----Original Message----- From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Jim Brown Sent: Saturday, September 3, 2022 10:43 PM To: main@WSJTX.groups.io Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal On 9/3/2022 4:23 PM, Eugene Morgan wrote: If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies. Takeoff angle is a flawed concept, because when the graphs are plotted, they set the strongest radiation to the outer limit of the circle, no matter how weak it is. The link I posted plots vertical patterns for ALL heights on the same graph, so it clearly shows what W4TV stated. See Fig 36 in http://k9yc.com/AntennaPlanning.pdf, which shows that 60 ft is optimum for 80M, and 90 ft is only 1 dB weaker. Divide those heights by 2 for 40M, as shown in Table 1. They are real, they are not a myth, and yes they can be fairly inefficient. And there is a tooth fairy. I suggest that you study the link I posted. It's based on an engineering study I did for the ARRL Antenna Book, where you'll see me listed as a contributor. W4TV is correct -- the earth is a big resistor, and the closer any wire carrying antenna current is to the earth the more of transmitter's power it burns (subtracted from the radiated signal). 73, Jim K9YC
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On 9/3/2022 4:23 PM, Eugene Morgan wrote: If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies. Takeoff angle is a flawed concept, because when the graphs are plotted, they set the strongest radiation to the outer limit of the circle, no matter how weak it is. The link I posted plots vertical patterns for ALL heights on the same graph, so it clearly shows what W4TV stated. See Fig 36 in http://k9yc.com/AntennaPlanning.pdf, which shows that 60 ft is optimum for 80M, and 90 ft is only 1 dB weaker. Divide those heights by 2 for 40M, as shown in Table 1. They are real, they are not a myth, and yes they can be fairly inefficient. And there is a tooth fairy. I suggest that you study the link I posted. It's based on an engineering study I did for the ARRL Antenna Book, where you'll see me listed as a contributor. W4TV is correct -- the earth is a big resistor, and the closer any wire carrying antenna current is to the earth the more of transmitter's power it burns (subtracted from the radiated signal). 73, Jim K9YC
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On 9/3/2022 12:53 PM, d_ziolkowski wrote: can you be more specific as to what is a myth? That very low antennas are much better for NVIS. 73, Jim K9YC
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On Saturday, September 3, 2022 at 07:16:25 PM CDT, Joe Subich, W4TV <lists@...> wrote: On 2022-09-03 7:23 PM, Eugene Morgan wrote: If I might clarify. NVIS Antennas are anything but a myth, and many > hams without realizing it use NVIS antennas. The "special properties" of NVIS antennas are a myth. Radiation at 90 degrees (straight up) from a horizontal dipole increases to a maximum at 1/4 wave above ground. However, the critical frequency (frequency at which RF passes through the ionosphere) is F(muf)*COS(@) where @ is the angle of incidence. For a 90 degree angle of incidence, F(crit) is *0 Hz* - IOW, 90 degree RF is not reflected *AT ALL* and RF close to 90 degrees is only reflected under rare conditions. At 60 degrees, the critical frequency is half the MUF ...IOW for NVIS at 20 meters the MUF needs to be above 10 meters for even 60 degree radiation! One is far better served to get the antenna above 0.32 wave high getting the peak lobe *DOWN* below 50 degrees where it will do some good. 73, ... Joe, W4TV On 2022-09-03 7:23 PM, Eugene Morgan wrote: If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
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The "special properties" of NVIS antennas are a myth. Hi Joe, There is a minor misunderstanding what MUF and critical frequency means. MUF is calculated from the critical frequency and is always higher than the critical frequency. Below the critical frequency the radio waves reflect back to ground. The angle of incidence for wave that goes direct vertical is zero i.e. cos(@) = 1. See e.g. https://en.wikipedia.org/wiki/Ionosonde. If you want to calculate the critical frequency from the MUF you need to know the @ that is used for the MUF calculation, normally distance is used instead of the incidence angle at the MUF definition. The @ is always less than 90 degrees for practical MUF values and so you will not end up to a *0 Hz* critical frequency. Lowest usable frequency (LUF) is mainly affected by the D layer absorption, but that's another story. 73, Reino OH3mA
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We may be splitting hairs, NVIS antennas are not a myth. As to their "special properties," I guess one would need to define what those special properties actually are. I've never been aware the NVIS's had any special properties. The math you refer in your email is exactly correct and can be demonstrated with any antenna modeling program. I completely agree, there isn't anything special about the NVIS antenna. Now if you want to talk about misunderstood antennas the G5RV would be at the very top of my particular list. ;-) But please let's not go into that here. This forum is about WSJT-X and I'd be happy to close this thread and get back to that.
Gene
(WB7RLX)
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-----Original Message----- From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV Sent: Saturday, September 3, 2022 6:16 PM To: main@WSJTX.groups.io Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal On 2022-09-03 7:23 PM, Eugene Morgan wrote: If I might clarify. NVIS Antennas are anything but a myth, and many > hams without realizing it use NVIS antennas. The "special properties" of NVIS antennas are a myth. Radiation at 90 degrees (straight up) from a horizontal dipole increases to a maximum at 1/4 wave above ground. However, the critical frequency (frequency at which RF passes through the ionosphere) is F(muf)*COS(@) where @ is the angle of incidence. For a 90 degree angle of incidence, F(crit) is *0 Hz* - IOW, 90 degree RF is not reflected *AT ALL* and RF close to 90 degrees is only reflected under rare conditions. At 60 degrees, the critical frequency is half the MUF ...IOW for NVIS at 20 meters the MUF needs to be above 10 meters for even 60 degree radiation! One is far better served to get the antenna above 0.32 wave high getting the peak lobe *DOWN* below 50 degrees where it will do some good. 73, ... Joe, W4TV On 2022-09-03 7:23 PM, Eugene Morgan wrote: If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
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On 2022-09-03 7:23 PM, Eugene Morgan wrote: If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. The "special properties" of NVIS antennas are a myth. Radiation at 90 degrees (straight up) from a horizontal dipole increases to a maximum at 1/4 wave above ground. However, the critical frequency (frequency at which RF passes through the ionosphere) is F(muf)*COS(@) where @ is the angle of incidence. For a 90 degree angle of incidence, F(crit) is *0 Hz* - IOW, 90 degree RF is not reflected *AT ALL* and RF close to 90 degrees is only reflected under rare conditions. At 60 degrees, the critical frequency is half the MUF ...IOW for NVIS at 20 meters the MUF needs to be above 10 meters for even 60 degree radiation! One is far better served to get the antenna above 0.32 wave high getting the peak lobe *DOWN* below 50 degrees where it will do some good. 73, ... Joe, W4TV On 2022-09-03 7:23 PM, Eugene Morgan wrote: If I might clarify. NVIS Antennas are anything but a myth, and many hams without realizing it use NVIS antennas. What most people don't realize is that almost any horizontal dipole like antenna (a traditional dipole, inverted vee, G5RV, OCF, half-wave wire, an end fed wire) suspended below 1/4 wavelength above real ground is an NVIS antenna, meaning they send most of their RF energy at high angles (above 45 degrees) and yes much of that energy is absorbed in the D layer or just continues on into space. Yes they are inefficient, yes they generally do not make good DX antennas. But they do have their place.
Model any HF dipole antenna and vary it's elevation from 1/8 of a wavelength to a full wavelength above ground and you will be able to see how the takeoff angle varies.
They are real, they are not a myth, and yes they can be fairly inefficient.
Gene
-----Original Message-----
From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 3, 2022 4:30 PM
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] How Do you connect 4U1UN ? #FreqCal
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
> can you be more specific as to what is a myth?
Low antennas (e.g., 15-20' above ground on 80/40 meters) for NVIS are a myth. Any horizontal antenna less than 1/4 wave above ground suffers significant loss. Maximum radiation is straight up but the "critical frequency" (frequency at which radiation at 90 degrees passes through the ionosphere) is generally well below even 80 meters most of the time. Even then, the D layer absorption during daylight kills most "straight up" RF on 80/40 meters.
Even for "close in" signals, one is best served by a dipole at approximately 50 feet for 80/40/30 meters and 35 feet for 20-10 meters.
73,
... Joe, W4TV
On 2022-09-03 3:53 PM, d_ziolkowski wrote:
Jim-
can you be more specific as to what is a myth?
And thanks for the link, I will study it.
Thanks Dan KC2STA
On Sat, Sep 3, 2022 at 3:02 PM Jim Brown <k9yc@...> wrote:
On 9/3/2022 2:43 AM, d_ziolkowski wrote:
Andre- yes I also can work closer in stations, but they may be using
NVIS antennas or nearly so. This is a myth. Study http://k9yc.com/AntennaPlanning.pdf
73, Jim K9YC
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