#calibration #frequency uBitx v5 #calibration #frequency

Tim Helming

Hello hive mind

I'm still trying to figure out some of the nuances of the interrelationships among the master calibration, sideband calibration, and BFO settings. There are two symptoms I am trying to resolve. They are both fairly minor but I'd like to get things really dialed in. 

Issue 1: Displayed frequency seems to be about 50Hz high (more detail below)
Issue 2: when sending PSK31, my transmitted signal as monitored on another radio seems to be sending the tones about 150Hz higher than what fldigi is acoustically producing (i.e. if I set fldigi to 1350 Hz and send PSK31, on my monitoring rig I'm hearing a tone of about 1500 Hz).

For issue 1, here's what I've observed. When listening carefully to SSB conversations, the voice tone is improved if I lower the dial frequency by about 50 Hz. This is the case whether I'm listening to USB or LSB. The other observation is that when using the built-in WSPR beacon on 14.097.100, most of the stations I get receipts from are showing something in the range of 14.097.147-153. There are some outliers--obviously most radios are a bit off, but the "consensus" is in the area of 50Hz high. So this accords with what I hear for the SSB voice tone.

My understanding is that the remedy for this is to change the master calibration. I used the formula given by Ian (CEC) to adjust the value, but this did not make an appreciable difference in my received signal frequency, even though I followed the math. So I also tried adjusting the calibration via the settings menu on the radio itself (I moved it by increments of 10 units at a time). Using this method, whether moving up or down, in either case the voice quality I'm hearing on SSB was worse--so I've kept returning to the "known-almost-good" value, with the same ~50Hz error. 

For issue 2, I'm a little confused about why I'm hearing a tone from my monitor that's ~150Hz high. I would have expected it to be ~50 Hz high, but it's definitely closer to 150. (I'm a musician and am pretty decent at matching pitches acoustically). And conversely, if I move the dial 150Hz down from the nominal frequency when listening to an SSB signal, the voice tone is definitely not as good as when I go only 50Hz down. Troubleshooting the BPSK issue, I tried changing the calibration value via the settings menu. This changed the quality of the monitored PSK31 tones--the tonal quality became rough--but the pitch did not change appreciably, which I would have expected it to do if I'm changing the radio's master frequency.

I'm testing all of this stuff on 20 meters, to reduce the number of variables I'm dealing with.

So here are a series of questions.
1) Anyone know why the discrepancy between SSB/WSPR (50 Hz error) and PSK31 tone (150 Hz error) would occur, especially since this is all on 20 meters? 
2) If changing the master calibration via the software (and the CEC error correction formula) gets my transmitted signal (as confirmed by WSPR receipts) closer to the right frequency, but SSB voice tone is then lousy, what is the other adjustment I need to make to balance it out? 
3) Should I be messing with the sideband calibration value to compensate for #2? Do I need to adjust that value proportionately to the master calibration value? I couldn't find any reference to doing so.
4) Does the BFO enter into this as well? I've tried adjusting that as well, and each value I've experimented with sounds worse than the value I've been using. 

Overall the radio is fantastic and I'm having a great time with it. I'm getting good signal reports and making contacts all over North America (and some WSPR to VK, ZL too). But I'd really like to iron out these frequency issues.



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