locked Calibrating external amp, CW vs FT8 readings #FT8 #TechnicalHelpQuestion


Dave Mueller AA3EE
 

HI,

If I calibrate an external amp in CW for 1000W, will FT8 be transmitting
more energy if the meter reads 1000W?
I'm asking because a bunch of guys on another group are talking about very
different metering (current and temps) when running FT8. I'm wondering if
some amps were calibrated in CW and some using FT8, and if FT8 is actually
generating more power in a given bandwidth than a CW signal since it's 50
Hz wide vs the practically 0 bandwidth for a CW signal.

When I worked in broadcast TV, I vaguely remember a formula using logs to
compare the power in two signals based on bandwidth, but can't
remember what it was.
My ancient HP8594E only goes down to 1KHz bandwidth, so I'm not sure I'd
get a valid reading.

Thanks
Dave AA3EE


Pietro Molina
 

Dave, it depends on many parameters, but using "tune" you will read the
maximum power output (peak power in SSB)
The problem is the effective power that your amplifier has to supportate.
SSB stresses the amplifier not more than 30%, CW 50% but digital modes such
FTx stress the amplifier to 100% for a long time. So, be careful and don't
ask for the full power to preserve the final from excess temperature.

Pietri I2OIM

Il giorno lun 1 ago 2022 alle ore 08:27 Dave Mueller AA3EE <
dmueller421@...> ha scritto:

HI,

If I calibrate an external amp in CW for 1000W, will FT8 be transmitting
more energy if the meter reads 1000W?
I'm asking because a bunch of guys on another group are talking about very
different metering (current and temps) when running FT8. I'm wondering if
some amps were calibrated in CW and some using FT8, and if FT8 is actually
generating more power in a given bandwidth than a CW signal since it's 50
Hz wide vs the practically 0 bandwidth for a CW signal.

When I worked in broadcast TV, I vaguely remember a formula using logs to
compare the power in two signals based on bandwidth, but can't
remember what it was.
My ancient HP8594E only goes down to 1KHz bandwidth, so I'm not sure I'd
get a valid reading.

Thanks
Dave AA3EE






Dennis W1UE
 

GM Dave

As a first approximation, I'd use an amplifier's RTTY rating as a starting
point for FTx. RTTY
is a 100% mode, so a 15 second RTTY transmission would stress the amp
equally to a
15 second FT8 transmission. I would keep the max output to no more than
the RTTY output
rating of the amp.

Depending on the amp, I may derate it or augment its cooling even more.

Dennis W1UE


On Mon, Aug 1, 2022 at 2:27 AM Dave Mueller AA3EE <dmueller421@...>
wrote:

HI,

If I calibrate an external amp in CW for 1000W, will FT8 be transmitting
more energy if the meter reads 1000W?
I'm asking because a bunch of guys on another group are talking about very
different metering (current and temps) when running FT8. I'm wondering if
some amps were calibrated in CW and some using FT8, and if FT8 is actually
generating more power in a given bandwidth than a CW signal since it's 50
Hz wide vs the practically 0 bandwidth for a CW signal.

When I worked in broadcast TV, I vaguely remember a formula using logs to
compare the power in two signals based on bandwidth, but can't
remember what it was.
My ancient HP8594E only goes down to 1KHz bandwidth, so I'm not sure I'd
get a valid reading.

Thanks
Dave AA3EE






Jim Brown
 

On 7/31/2022 4:14 PM, Dave Mueller AA3EE wrote:
If I calibrate an external amp in CW for 1000W, will FT8 be transmitting
more energy if the meter reads 1000W?
It depends on the meter, and what how you put the rig into TX mode to read power. First, CW is not continuous, it's 100% amplitude modulation of a carrier by a rectangular wave train, so when sending CW, a meter that reads average power will read considerably less than 1kW; but a fast peak reading meter that catches and holds peaks will read 1kW; and that same meter that does NOT hold peaks will fluctuate up and down. I use an LP-100A, which can read average, peak and hold, and continuous peak.

If you measure CW power with a keydown transmission, all of the meters should read the same, and will read the same when you're transmitting FT8.

But you said energy, and both modes have a duty cycle. FT8 has a duty cycle of about 40% (the programmers will correct me). For CW, the duty cycle is pretty variable, depending both on what you're sending and how long you send and how long you listen.

I'm a contester, and the most demanding duty cycles I encounter are on RTTY when I'm calling CQ and getting few answers.

73, Jim K9YC


Dave Mueller AA3EE
 

Jim, I have an HP435B with an 8284B average power sensor.
I think my issue is not knowing how to figure out peak vs average power for the modulated modes. If a transistor is rated for 1KW CW, but a mode has a high peak to average power, then I need to know so that I don't exceed the 1KW rating.

Thanks all for the replies.


Reino Talarmo
 

I think my issue is not knowing how to figure out peak vs average power for the modulated modes. If a transistor is rated for 1KW CW, but a mode has a high peak to average power, then I need to know so that I don't exceed the 1KW rating.
Normally power amplifiers/transistors are defined in amateur purposes for an intermittent use e.g. CW. CW means in that case On-Off modulation using e.g. Morse code and a certain transmit/receive ratio. Without knowing how those are defined in your case we can only guess what could be the equivalent continuous power that can be used. A wild guess is one half or so. Some sources say 30 %. The 1 kW usually means power during a short tuning session i.e. carrier power.

It really depends what lifetime of the transistor is expected. The achieved lifetime depend strongly how hot is the chip inside the transistor. It really means inside, not the heatsink. For FT8 the temperature of the heatsink and of course of the transistor rises faster than in CW (Morse code) due to about 13 s continuous transmission. In CW average power is typically less than 50 % of the carrier power during transmission.

It is totally different issue what power typical amateur power meter really indicates. Your average power meter may give a more realistic value depending possible additional filtering. Most probably averaging time is much less than say 10 s and it does not alone tell the whole story about temperature rise.

73, Reino OH3mA


Jim Brown
 

On 8/1/2022 12:59 PM, Dave Mueller AA3EE wrote:
I think my issue is not knowing how to figure out peak vs average power for the modulated modes.
Dave,

Power ratings are based on several design factors, including voltage and current ratings for all the components in the related circuitry. In one popular solid state power amp, power handling and duty cycle on 6M, where it is least efficient, is limited not by the output devices, but by I-squared R losses in an inductor in the output circuit. If it gets too hot, it melts the solder holding them to the circuit board and falls out (they're upside down). It's a non-destructive failure -- the amp protects itself, so re-soldering the inductor(s) solves the problem.

Operationally, the solution is simple -- don't push the amp too hard on 6M with modes with long key-down periods.

Capacitors have both voltage and current ratings, and those ratings often depend on temperature.

73, Jim K9YC


Martin G0HDB
 

On Mon, Aug 1, 2022 at 07:27 AM, Dave Mueller AA3EE wrote:


HI,

If I calibrate an external amp in CW for 1000W, will FT8 be transmitting
more energy if the meter reads 1000W?
No, because at any instant an FT8 signal comprises a single 'tone' that's somewhere in the audio passband between say 200 and 3500Hz. If you've calibrated something, be it an external amp or whatever, so that it reads 1000W when sending a continuous signal, eg. by holding down a Morse key when the rig is in CW mode, then an FT8 signal should also give you a reading of 1000W. However...

Because there can be slight variations in the frequency response of a transmitter across the audio passband you might find that an FT8 signal doesn't always give a reading of exactly 1000W - it might vary by a small amount (hopefully <1dB) depending on just how much ripple there is across the audio passband.

It's worth remembering that an FT8 signal isn't a composite signal that contains many different frequencies simultaneously, as a voice SSB signal does. Because the FT8 signal only ever comprises a single tone at any instant, transmitting an FT8 signal doesn't require linear amplification - a Class C amplifier should be perfectly adequate (in theory at least!).

--
Martin G0HDB


Pietro Molina
 

It's true only if the audio level is well regulated (or overdrive...) the
rig input. If the level is too low you will read less then with CW key down.

Pietro I2OIM

Il giorno mar 2 ago 2022 alle ore 17:02 Martin G0HDB <marting0hdb@...>
ha scritto:

On Mon, Aug 1, 2022 at 07:27 AM, Dave Mueller AA3EE wrote:


HI,

If I calibrate an external amp in CW for 1000W, will FT8 be transmitting
more energy if the meter reads 1000W?
No, because at any instant an FT8 signal comprises a single 'tone' that's
somewhere in the audio passband between say 200 and 3500Hz. If you've
calibrated something, be it an external amp or whatever, so that it reads
1000W when sending a continuous signal, eg. by holding down a Morse key
when the rig is in CW mode, then an FT8 signal should also give you a
reading of 1000W. However...

Because there can be slight variations in the frequency response of a
transmitter across the audio passband you might find that an FT8 signal
doesn't always give a reading of exactly 1000W - it might vary by a small
amount (hopefully <1dB) depending on just how much ripple there is across
the audio passband.

It's worth remembering that an FT8 signal isn't a composite signal that
contains many different frequencies simultaneously, as a voice SSB signal
does. Because the FT8 signal only ever comprises a single tone at any
instant, transmitting an FT8 signal doesn't require linear amplification -
a Class C amplifier should be perfectly adequate (in theory at least!).

--
Martin G0HDB






Dave Mueller AA3EE
 

Martin, I thought FT8 transmitted 3 tones simultaneously in the 50 Hz bandwidth, which is why I originally asked the question.
If you're right and it's a single carrier at a time, then I understand everything completely. RTTY is the same, except potentially longer transmissions.


William Smith
 

8 tones (3 bits), hence FT8, but only one at a time.

73, Willie N1JBJ

On Aug 2, 2022, at 7:56 PM, Dave Mueller AA3EE <dmueller421@...> wrote:

Martin, I thought FT8 transmitted 3 tones simultaneously in the 50 Hz bandwidth, which is why I originally asked the question.
If you're right and it's a single carrier at a time, then I understand everything completely. RTTY is the same, except potentially longer transmissions.


Reino Talarmo
 

Martin, I thought FT8 transmitted 3 tones simultaneously in the 50 Hz bandwidth, which is why I originally asked the question.
If you're right and it's a single carrier at a time, then I understand everything completely. RTTY is the same, except potentially longer transmissions.

Hi Martin,
There is an excellent description how FT8 works in the reference material nro 33 https://www.physics.princeton.edu/pulsar/K1JT/FT4_FT8_QEX.pdf. It is mainly talking about decoding and protocol and only shortly how FSK modulation is made very narrow band using GMSK to tame frequency shifts.

73, Reino OH3mA


Martin G0HDB
 

On Wed, Aug 3, 2022 at 06:03 AM, Reino Talarmo wrote:

Hi Martin,
There is an excellent description how FT8 works in the reference material nro
33 https://www.physics.princeton.edu/pulsar/K1JT/FT4_FT8_QEX.pdf. It is mainly
talking about decoding and protocol and only shortly how FSK modulation is
made very narrow band using GMSK to tame frequency shifts.
Hi Reino, I was already aware of the QEX document about FT4/8, but thanks for the link anyway!

As far as I can see, the modulation used by FT4/8 is GFSK, ie. Gaussian-filtered FSK, as opposed to GMSK, which I believe is a different beast altogether.

The QEX paper is well worth reading by anyone who wants to get a better understanding of how FT4/8 work at the modulation and decoding levels; with regard to the former the paper includes the following statements:

"FT4 and FT8 waveforms have constant amplitude except at the very beginning and end of a transmission. FT8 signals are ramped up gradually over a transition interval T/8, or 20 ms, at the beginning of the first sync symbol. The ramp function is a raised cosine ... The same taper is used in reverse to gradually ramp down the signal at the end of the transmission ... FT4 waveforms are similarly soft-keyed."

73
--
Martin G0HDB


Reino Talarmo
 

Hi Reino, I was already aware of the QEX document about FT4/8, but thanks for the link anyway!
Sri Martin I intended to send that message to Dave, hi!
I respect your knowledge on telecommunications.

73, Reino OH3mA


Bill, WB6JJJ
 

Being a single tone sent at a time, I don’t understand why my ICOM PW-1 amplifier will transmit at a maximum of 500 Watts in FT8/4.
It will output 1000 Watts key down, CW and RTTY.
I can maybe understand the lower maximum power if there were multi tones.
This 500 Watt issue has been confirmed with other PW-1 users.
Any thoughts?
Thanks,
Bill
WB6JJJ

On Aug 2, 2022, at 9:44 PM, William Smith <w_smith@...> wrote:

8 tones (3 bits), hence FT8, but only one at a time.

73, Willie N1JBJ

On Aug 2, 2022, at 7:56 PM, Dave Mueller AA3EE <dmueller421@...> wrote:

Martin, I thought FT8 transmitted 3 tones simultaneously in the 50 Hz bandwidth, which is why I originally asked the question.
If you're right and it's a single carrier at a time, then I understand everything completely. RTTY is the same, except potentially longer transmissions.





Michael Black
 

Perhaps your audio levels from WSJTX to the rig are down 3dB?
Windows playback level at 0dB -- WSJTX at full power -- then adjust audio level to rig (via soundcard or rig menu) to bring up the power.
What rig do you have and do you have a sound card?
My paper on setting audio levels should be of use.https://www.dropbox.com/s/hlt50x44qs2ua1f/FT8Noise8.pdf?dl=0

Mike W9MDB

On Wednesday, August 3, 2022 at 11:23:57 AM CDT, Bill, WB6JJJ <bill@...> wrote:

Being a single tone sent at a time, I don’t understand why my ICOM PW-1 amplifier will transmit at a maximum of 500 Watts in FT8/4.
It will output 1000 Watts key down, CW and RTTY.
I can maybe understand the lower maximum power if there were multi tones.
This 500 Watt issue has been confirmed with other PW-1 users.
Any thoughts?
Thanks,
Bill
WB6JJJ



On Aug 2, 2022, at 9:44 PM, William Smith <w_smith@...> wrote:

8 tones (3 bits), hence FT8, but only one at a time.

73, Willie N1JBJ

On Aug 2, 2022, at 7:56 PM, Dave Mueller AA3EE <dmueller421@...> wrote:

Martin, I thought FT8 transmitted 3 tones simultaneously in the 50 Hz bandwidth, which is why I originally asked the question.
If you're right and it's a single carrier at a time, then I understand everything completely. RTTY is the same, except potentially longer transmissions.





Bill, WB6JJJ
 

Thanks Mike,
I doubt it since the ICOM IC-7610 power output without the amplifier is 100 Watts. I need to turn down the power to about 20 Watts before the amplifier output starts to drop from 500 Watts.
Bill
WB6JJJ

On Aug 3, 2022, at 9:31 AM, Michael Black via groups.io <mdblack98@...> wrote:

Perhaps your audio levels from WSJTX to the rig are down 3dB?
Windows playback level at 0dB -- WSJTX at full power -- then adjust audio level to rig (via soundcard or rig menu) to bring up the power.
What rig do you have and do you have a sound card?
My paper on setting audio levels should be of use.https://www.dropbox.com/s/hlt50x44qs2ua1f/FT8Noise8.pdf?dl=0

Mike W9MDB



On Wednesday, August 3, 2022 at 11:23:57 AM CDT, Bill, WB6JJJ <bill@...> wrote:

Being a single tone sent at a time, I don’t understand why my ICOM PW-1 amplifier will transmit at a maximum of 500 Watts in FT8/4.
It will output 1000 Watts key down, CW and RTTY.
I can maybe understand the lower maximum power if there were multi tones.
This 500 Watt issue has been confirmed with other PW-1 users.
Any thoughts?
Thanks,
Bill
WB6JJJ



On Aug 2, 2022, at 9:44 PM, William Smith <w_smith@...> wrote:

8 tones (3 bits), hence FT8, but only one at a time.

73, Willie N1JBJ

On Aug 2, 2022, at 7:56 PM, Dave Mueller AA3EE <dmueller421@...> wrote:
Martin, I thought FT8 transmitted 3 tones simultaneously in the 50 Hz bandwidth, which is why I originally asked the question.
If you're right and it's a single carrier at a time, then I understand everything completely. RTTY is the same, except potentially longer transmissions.















Michael Black
 

Do you have ALC feedback connected to the rig?
Mike W9MDB

On Wednesday, August 3, 2022 at 02:08:57 PM CDT, Bill, WB6JJJ <bill@...> wrote:

Thanks Mike,
I doubt it since the ICOM IC-7610 power output without the amplifier is 100 Watts.  I need to turn down the power to about 20 Watts before the amplifier output starts to drop from 500 Watts.
Bill
WB6JJJ

On Aug 3, 2022, at 9:31 AM, Michael Black via groups.io <mdblack98@...> wrote:

Perhaps your audio levels from WSJTX to the rig are down 3dB?
Windows playback level at 0dB -- WSJTX at full power -- then adjust audio level to rig (via soundcard or rig menu) to bring up the power.
What rig do you have and do you have a sound card?
My paper on setting audio levels should be of use.https://www.dropbox.com/s/hlt50x44qs2ua1f/FT8Noise8.pdf?dl=0

Mike W9MDB



    On Wednesday, August 3, 2022 at 11:23:57 AM CDT, Bill, WB6JJJ <bill@...> wrote: 

Being a single tone sent at a time, I don’t understand why my ICOM PW-1 amplifier will transmit at a maximum of 500 Watts in FT8/4.
It will output 1000 Watts key down, CW and RTTY.
I can maybe understand the lower maximum power if there were multi tones.
This 500 Watt issue has been confirmed with other PW-1 users.
Any thoughts?
Thanks,
Bill
WB6JJJ



On Aug 2, 2022, at 9:44 PM, William Smith <w_smith@...> wrote:

8 tones (3 bits), hence FT8, but only one at a time.

73, Willie N1JBJ

On Aug 2, 2022, at 7:56 PM, Dave Mueller AA3EE <dmueller421@...> wrote:
Martin, I thought FT8 transmitted 3 tones simultaneously in the 50 Hz bandwidth, which is why I originally asked the question.
If you're right and it's a single carrier at a time, then I understand everything completely. RTTY is the same, except potentially longer transmissions.















Hank Pfizenmayer
 

How are you measuring the power out of the 7610 -with its internal wattmeter? If you are in WSJTX - the "tune" is a CW carrier at same level as the FT8 signal. See what power is in"tune" ,then use "Enable Tx and set Tx even/first so it goes into FT8 TX and read the output power. It should be essentially the same in both cases . If not , something is not right with a 7610 or WSJT audio level setting -

DO THIS ALL WITH AMP OFF until you get same output from the 7610 on FT8 and CW.

I don't anything about the PW1 or 7610 settings etc.

But Is there ALC connection between the 7610 and the PW1 -maybe the 7610 does something different between "data" whatever they call it and CW.

Hank K7HP


Bill, WB6JJJ
 

Hi Hank,
Yes, all modes including the WSJT tune mode indicate 100 Watts on the power meter.
I need to dig into the PW-1 and 7610 manuals to see if there is anything mentioned about this issue. Like Mike said, it may be something to do with ALC - maybe only in the USB-DATA mode used by the WSJT program.
Regards,
Bill
WB6JJJ

On Aug 3, 2022, at 11:24 PM, Hank Pfizenmayer via groups.io <pfizenmayer@...> wrote:

How are you measuring the power out of the 7610 -with its internal wattmeter? If you are in WSJTX - the "tune" is a CW carrier at same level as the FT8 signal. See what power is in"tune" ,then use "Enable Tx and set Tx even/first so it goes into FT8 TX and read the output power. It should be essentially the same in both cases . If not , something is not right with a 7610 or WSJT audio level setting -

DO THIS ALL WITH AMP OFF until you get same output from the 7610 on FT8 and CW.

I don't anything about the PW1 or 7610 settings etc.

But Is there ALC connection between the 7610 and the PW1 -maybe the 7610 does something different between "data" whatever they call it and CW.

Hank K7HP