Re: uBitx VFO VFO frequency deviation 700 Hz at 80 meters; 1400 Hz at 40 meters ... #ubitx #radiuno #calibration


What software are you using in your v5 uBitX, John? I know my v4.3 sketch did not follow the described sequence on the HFSignals site and when put into calibration it started transmitting on 10mHz. Once I figured out what it was doing, calibration was relatively simple with a second receiver. I set the other receiver to 10mhz and put a dummy load on the uBitX. Then while in calibration mode I adjusted the VFO until the signal was dead on 10mHz.

Since then I have changed to the KD8CEC sketch and calibration is different there, using the old HFSignals method, i assume. When in calibration it is put into receive and you need to be monitoring a strong AM carrier where you can hear the beat note, then you adjust the VFO until you have zero beat. Since you cannot really hear the low frequencies, getting "zero beat" really means centering the calibration between the upper and lower beat notes of the same frequency and you can confirm by comparing the sound of an AM signal between USB and LSB. If it is calibrated right, they will sound the same.

Also, i know some folks have some confusion about what is meant by zero beat. When you listen to an AM signal with an SSB receiver you will hear a tone that is the difference between the AM carrier and the injected carrier used for SSB. The greater the difference the higher pitch or frequency is the tone. As you get closer to being on the same frequency the difference gets less and less and the pitch gets lower and lower until it is zero. As you pass the zero point the difference and pitch starts increasing on the other side, too. When you are very close, below 100 cycles, for example, you are usually below the audio passband, but you can sometimes hear the low "pulsing" of the audio right down to a few times per second, which is still the "beat note" difference between frequencies.


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