Re: New V5 build results and calibration issues. #ubitx #ubitx-help #calibration #nextion

Roman
 

An update on the BFO adjustment - It turns out that the info I gave about adjusting for the lowest pitch is wrong. If not adjusted correctly, you may end up transmitting both the signal AND the carrier if the filter has been shifted too far (wrong BFO adjustment). For SSB the carrier needs to be suppressed, but it is possible to have the carrier transmitting unintentionally. I found this out while trying to transmit FT8 signals and seeing two spikes on my SDR (running using a separate tiny antenna and laptop in the other room).

I've found the only reliable approach that doesn't involve complex test instruments is to download and use an audio spectrum analyzer program. This is confirmed in other posts I've seen. The one I stumbled upon that seemed to do the job is SpectrumView by WD6CNF.

Here is a procedure that will get you in the ballpark:

1. Disconnect antenna from ubitx, or better, find an unused part of the band with just hiss, no other signals
2. Run audio out from ubitx into PC/Mac/Linux audio in
3. Run spectrum analyzer and configure it to listen to the audio in
4. Turn up volume on ubitx until levels are reasonably high but not clipping in the spectrum analyzer
5. For the ubitx 5 (not the earlier versions), you will want to set the BFO somewhere around 11.055-11.056 MHz as a starting point.
6. I am going to presume that you started with the BFO frequency on the high side, say 11.057 and you are lowering it. As you do so, you should see on the spectrum analyzer that the noise's high frequency roll off frequency increase. At some point it will no longer get any higher no matter what you do with the BFO value. The point you want is right as you touch that max value. You might have to back off and watch the max value decrease, then adjusting again until you find the maximum.
7. Save the BFO frequency using the PTT where you get maximum high frequency response. I found that the BFO frequency was about 1.5-2 kHz lower than the frequency where the I got the most "bass" response in my headphones, thus the final result had less bass response.
8. If you have an SDR, you can double-check your results: Run ubitx into a dummy load and have an SDR with separate tiny (or no) antenna nearby, either run WSJT-X "Tune", or a single frequency of audio into the ubitx mic. The SDR will likely be sensitive enough to pick up stray RF (even with the dummy load) and you should be able to see only one, not two spikes on the display (make sure you zoom in maximum to a narrow bandwidth view).

After this adjustment, I've managed to make a few longer distance FT8 contacts, i.e. Seattle to Alaska on 40m.

I know the procedures I've written are long and seem complicated, but I do that on purpose to give the most information possible especially for those who may be stuck on some detail they read elsewhere. I do have one caveat: If you have a properly factory tuned ubitx, I would not recommend adjusting the ubitx calibration or BFO.

Hope this info helps someone,
Roman K7TXL

Join BITX20@groups.io to automatically receive all group messages.