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Re: Simple UBITX Test Set

 

Tom,

I have no idea what the calibration routine on the uBitx looks like now for the various variants of the firmware.
Here's my critique of the original uBitx firmware, and how I thought it should be done, and how radio works:
? ??/g/BITX20/message/35235
? ??/g/BITX20/message/44278
? ??/g/BITX20/message/44515

Assume that when zero beating, you can detect by ear an AC waveform down to 20hz.
With a 1mhz carrier in the AM broadcast band, you get an accuracy of within 20 ppm after calibrating
If you use a 10mhz shortwave AM broadcast, the accuracy is 2ppm.

Shortwave AM broadcasts are a wasteland compared to what we had 50 years ago,
(as are most of the public airwaves here in the US) but they almost always put out a very accurate carrier.

I thought I was able to get a good zero beat on WWV a couple years ago when I last tried it,
though I did have to wait a minute for a quiet part of the broadcast.

Below 20hz, you won't necessarily hear much.
Especially given the AC coupling caps in the audio chain of the uBitx.
One possibility for more accurately finding zero beat would be to monitor the demodulator's audio
somehow using a Nano analog pin.

Jerry, KE7ER


On Tue, Oct 27, 2020 at 08:48 AM, Tom, wb6b wrote:
One additional thing occurred to me. Rather than try to calibrate the dial frequency by attempting to zero beat WWV or listen to the sound of an AM radio station, it might be a good idea to have a test connection point to attach a short piece of wire to one of the?Si5351 outputs and be able to dial the frequency to a known AM radio station and listen for the zero beat on an AM radio. (Likely everyone has an AM radio) Then whatever the difference between the frequency display and the known AM radio station frequency could be input to zero/calibrate the the uBitx dial frequency. Should be simpler, more direct and reliable than the current method to calibrate the dial frequency (unless the calibration method has been updated in the last year or so). Not sure how accurate the DVMs are as frequency counters, but still a great way to ballpark check things.
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