Date
1 - 20 of 20
Locked staying in your lane #NewUser
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Bob W7DIT
I always click on a 50Hz boundary before transmiting and most other operators do too. If this is the convention, I wonder why WSJT-X doesn't, by default, override us to do that. Lately, I've noticed some operators straddle the boundries and overlap with my signal. Perhaps there is a reason WSJT-X enables operators to operate across 50Hz boundries and I don't know it. Perhaps the 50Hz boundry convention is a myth. I'm eager to learn.
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The 50Hz boundary is a complete myth. FT8/Ft4 will be happy anywhere in the audio pass-band.
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Larry / W1DYJ On 8/25/2022 13:15, Bob W7DIT wrote:
I always click on a 50Hz boundary before transmiting and most other operators do too. If this is the convention, I wonder why WSJT-X doesn't, by default, override us to do that. Lately, I've noticed some operators straddle the boundries and overlap with my signal. Perhaps there is a reason WSJT-X enables operators to operate across 50Hz boundries and I don't know it. Perhaps the 50Hz boundry convention is a myth. I'm eager to learn. |
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Al Groff
I was never aware of any 50hz boundary and I have ten of thousands of ft8 contacts in the log.
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There is a slightly better chance of copying two stations if they are off by a few hz rather than precisely on the same frequency. The software is amazing! AL, K0VM On 8/25/2022 12:15 PM, Bob W7DIT wrote:
I always click on a 50Hz boundary before transmiting and most other operators do too. If this is the convention, I wonder why WSJT-X doesn't, by default, override us to do that. Lately, I've noticed some operators straddle the boundries and overlap with my signal. Perhaps there is a reason WSJT-X enables operators to operate across 50Hz boundries and I don't know it. Perhaps the 50Hz boundry convention is a myth. I'm eager to learn. |
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For the last few release versions and the rc's, I've had 2 and sometimes 3 stations on exactly the same offset or so very near, and all decoded, however there may have been even more. This happens down to -20 and below.
-- 73's George - WB5JJJ Hamshack Holine #4969 Hams over IP #100105 |
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Don Roden
Please explain W4DNR
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On 2022-08-25 12:15 pm, Bob W7DIT wrote:
I always click on a 50Hz boundary before transmiting |
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M0PWX
The spec is
From FT8 Digital Radio Protocol—How Does it Work? | by Dmitrii Eliuseev | Dev Genius<https://blog.devgenius.io/ft8-digital-radio-protocol-how-does-it-work-745bceae11f0> FT8 features: The message length is 15s, messages are transmitting via fixed time-slots, that makes decoding easier. Message length is 77 bit + 12-bit CRC. Error correction FEC LDPC(174,87). Frequency modulation 8-FSK, tone space is 6.25Hz. The bandwidth is 50Hz. Using this bandwidth, lot’s of stations can be decoded in parallel. Decoding limit is -20dB. Optional possibility of work automation. So there is a lot of space in between tones, hence multiple signals can overlap and still decode, joe did a fantastic job when he designed this protocol And remember only 1 of the 8 tones is TX at any time so the waterfall is actually a misrepresentation of how crowded the spectrum is The biggest problem I have is when you get a strong station overlapping a weaker station then you do tend to lose the decode of the weaker station Peter M0PWX M0PWX Grabber Page (qsl.net)<https://www.qsl.net/m0pwx/grabbers.htm> From: WB5JJJ - George<mailto:wb5jjj@...> For the last few release versions and the rc's, I've had 2 and sometimes 3 stations on exactly the same offset or so very near, and all decoded, however there may have been even more. This happens down to -20 and below. |
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Chuck Gelm
On 8/25/22 13:15, Bob W7DIT wrote:
I always click on a 50Hz boundary before transmiting and most other operators do too. If this is the convention, I wonder why WSJT-X doesn't, by default, override us to do that. Lately, I've noticed some operators straddle the boundries and overlap with my signal. Perhaps there is a reason WSJT-X enables operators to operate across 50Hz boundries and I don't know it. Perhaps the 50Hz boundry convention is a myth. I'm eager to learn.Hi, Bob: I think that it is quite common for stations to be +/- 10 Hz calibrated. Judging by PSKReporter reports of my signal. 73, Chuck |
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Jeff Stillinger
From days long ago.... This goes all the way back to Version 1.6, before FT8 and when JT65 was king of the hill. It's how we got more bandwidth.
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In the lab testing under "perfect" conditions. Signals can overlap with a 1 Hz separation and still achieve decode. However, when we add to the mixture band noise and signal variations between many different radios. Practical use, we could squeeze in with 5 Hz separation. Add the desensitizing from the increased speed of FT8, and in practical use, 10 Hz separation is all that is needed to achieve decode. I have been able to move in even closer, but requires that I pay closer attention to what I am doing. It's perfectly fine to have over lapping signals. You do not need a perfectly clear space. No one is "stepping on" you. WSJT-X is a non-traditional mode, so what you know about SSB or CW does not apply. Meaning that just because someone is 7-10 Hz away, does not man you need a KW to break a pile up, because there is no pile up. Have fun and enjoy... On 8/25/22 12:15, Bob W7DIT wrote:
I always click on a 50Hz boundary before transmiting and most other operators do too. If this is the convention, I wonder why WSJT-X doesn't, by default, override us to do that. Lately, I've noticed some operators straddle the boundries and overlap with my signal. Perhaps there is a reason WSJT-X enables operators to operate across 50Hz boundries and I don't know it. Perhaps the 50Hz boundry convention is a myth. I'm eager to learn. |
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Martin G0HDB <marting0hdb@...>
On Thu, Aug 25, 2022 at 06:56 PM, M0PWX wrote:
The spec isBeing pedantic, the message length is not 15secs - the protocol spec for FT8 states that the Tx duration, and hence the message length, is 12.6secs. Of course, this is within a 15sec time-slot. As others have already pointed out, there are no boundaries - 50Hz or otherwise - across the entirety of the audio passband. Anyone can transmit wherever they want and the software will decode the signals often even in the presence of strong co-channel QRM. I think the greatest differential I've noticed between two signals within a Hz or two of each other was about 20dB, which was pretty astonishing! -- Martin G0HDB |
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Bob W7DIT
Thank you everyone, I am smarter now!
So you don't think I made-up the "staying in your lane" concept, I heard about it in a Ham Radio Crash Course YouTube video called "Top 6 Tips For Digital HF Ham Radio, WSJT-X, FT8, JS8CALL <https://www.youtube.com/watch?v=4aXGOBI4P04&ab_channel=HamRadioCrashCourse>". He listed it as Tip #1. |
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He knows not of which he speaks... He has misinterpreted the 50 Hz "bandwidth" of an FT8 signal.
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Larry / W1DYJ On 8/25/2022 16:22, Bob W7DIT wrote:
Thank you everyone, I am smarter now! |
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Robert Lorenzini
And remember only 1 of the 8 tones is TX at any time so the waterfall is actually a misrepresentation of how crowded the spectrum isIf you run SpectrumLab (free) on a ft8 band you will see how true this is. Bob - wd6dod |
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Reino Talarmo
And remember only 1 of the 8 tones is TX at any time so the waterfall is actually a misrepresentation of how crowded the spectrum is The biggest problem I have is when you get a strong station overlapping a weaker station then you do tend to lose the decode of the weaker station If you run SpectrumLab (free) on a ft8 band you will see how true this is.Hi FT8 uses all 8 frequencies for a message transmission, one at the time. The receiver looks all those 8 frequencies as it needs to detect which one is sent. Frequency spectrum of a signal is the total transmitted tones i.e. about 50 Hz for FT8. Actually it is about 3 to 6 Hz wider due to the "fast" frequency shifts depending how spectrum width is defined. FT8 uses and needs the whole 50+ Hz bandwidth for a successful reception. Each tone as such require about 6.25 Hz bandwidth for a "perfect" transmission and reception. In that sense a second signal affects to decoding about the same amount within 6 Hz frequency difference including 0 Hz difference. By the way there are three dimensions that affect to the decoding probability of two signals on the same frequency slot. Everybody knows signal strength and frequency difference, but also time difference has a strong effect. A time difference of more than a symbol length 160 ms may be enough even, when signal strengths are the same and there is no frequency difference. 73, Reino OH3mA |
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Larry
You are correct, but the myth may be reinforced by the way wsjt-x turns your transmit off if the station you are contacting is in QSO with another station AND your frequency overlaps with the 50hz used by the station you are trying to contact. If you set your tx frequency outside that boundary, you don’t have an issue. I have also had many occasions where I have decoded 2 and sometimes 3 stations on exactly the same frequency. I guess that slight frequency deviations and timing differences are helping the software to resolve the decodes. -- Steve M0NMA |
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I tend to move up or down in 50Hz sections. However, the shortcut "Shift-F11" moves the TX frequency down 60Hz and "Shift-F12" moves the TX frequency up by 60Hz. On FT4 it's 90Hz.
There are probably many reasons why people might not be exactly so many hertz up or down from your offset frequency. 1. Their transceiver calibration is off (I would guess that not many people have carried out the FreqCal procedure and set the 'slope' and 'intercept' for their radio based upon checking against known frequency standards. See Section 13.1. Frequency Calibration in the WSJT-X User Guide) 2. They have either set an offset frequency manually, or they have gone up or down a few Hertz to avoid another station. 3. They've used some combination of the keyboard shortcuts, see "Keyboard shortcuts" under the Help menu in WSJT-X. |
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Hi Steve,
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The myth is reinforced because people make assumptions and don't read the excellent information about how WSJT-X works. AND, even if your and my rigs displayed the same frequency number on their front panels no rig has perfect calibration, so they would not be on the same frequency. The concept that you and I can dial in a number ending in "50" and be in the same place on the spectrum is quite totally false in reality. Larry / W1DYJ On 8/26/2022 4:58, Steve marsh (M0NMA) wrote:
Larry |
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Robert Lorenzini
Steve all that you say is true but more and more of us are using GPSDO's to
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control frequency. In this case atmospheric effects are the largest variable. Bob - wd6dod On 8/26/2022 5:48 AM, Larry Banks via groups.io wrote:
Hi Steve, |
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Darl DEEDS
How can you possibly imply that most other operators do to?? I do NOT. No reason too. I just make contacts and don’t worry about all these myths.
NA8W From: Bob W7DIT<mailto:cent@...> Sent: Thursday, August 25, 2022 13:15 To: main@WSJTX.groups.io<mailto:main@WSJTX.groups.io> Subject: [WSJTX] staying in your lane #NewUser I always click on a 50Hz boundary before transmiting and most other operators do too. If this is the convention, I wonder why WSJT-X doesn't, by default, override us to do that. Lately, I've noticed some operators straddle the boundries and overlap with my signal. Perhaps there is a reason WSJT-X enables operators to operate across 50Hz boundries and I don't know it. Perhaps the 50Hz boundry convention is a myth. I'm eager to learn. |
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Bob W7DIT
don’t worry about all these myths . . .I operate QRP with my FT-818 and dipole. I have to use every advantage to make challenging contacts. Bob. W7DIT |
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Gary - AG0N
On Aug 25, 2022, at 13:07, Martin G0HDB <marting0hdb@...> wrote:It’s better than that. Several times over the last few years, I’ve decoded two stations on the exact same frequency (according to the decoded line readout). I first started seeing this on JT65 in the latter days before FT8 came along. Gary - AG0N |
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