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For ME, anyway, a huge success this morning:? ?was able to measure both the BFO (crystal) and Raduino base (crystal) frequencies and then upload sketches with corrected values -- should essentially elminate the need for calibrating (I hope).? ?The goal of all this was to be able to correctly? transmit to WINLINK gateways, which rquire that you be within 200 Hz of the correct frquency.? ?Since I now have my raduino modified to allow both 80 and 40 meter performance, I wanted it to be on correct frquency no matter where I went, and a previous poster had already indicated measuring the internal crystals was the most straightforward way to do this.??

1.? I have available an ICOM-718 with digital freq readout; tuned it to WWV at 10 MHz at a time when receivable.? ?You can use upper sideband and tune for beat with the carrier, or offset exactly 500 Hz on the transceiver and then measure the audio frequency (e.g, with the waterfall display from FLDIGI or SOUNDMODEM or any other sound card program) --- my ICOM 718 was within 20 Hz.? ?

(I also tried to calibrate an ancient freq counter, which worked, but later I was unable to measure the bfo output even after the emitter follower with this device, so I gave up that approach.....using the calibrated ham receiver worked a lot easier anyway!!)

2. Knowing the ham transceiver's internal freq is accurate, I simply connected a test clip to the center of the antenna coax and dangled it near the bfo section of the BITX (at first I even put a resistors, 2000 ohms, in series but not necessary) --- just having the wire near the circuit I was able to pick up the BFO frequency quite easily and measure its frequency by going to the null on the carrier

I have two BITX's, one called "plywood" and the other called "breadpan" for how they are mounted:

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?BFO FREQUENCY

BREADPAN? ? ? ? ? 11998.92 kHz

PLYWOOD? ? ? ? ? ? 11998.26 kHz

3.? Using a sketch where I intentionally forced the RADUINO to produce 25.00000000000 MHz (that of its underlying crystal), I loaded that sketch and then dangled the wire near the output of the raduino and again looked for the signal with my ICOM-718 transciever:

? ? ? ? ? ? ? ? ? ? ? ? ? ? ?RADUINO FREQUENCY

BREADPAN? ? ? ?25004.460 kHz

PLYWOOD? ? ? ? 25004.560 kHz

4.? I then compiled individual sketches (based on Allards wonderful 1.24 sketch)? for each of the two bitx's, using their individual BFO and Raduino cyrstal frequencies:

for example, for the plywood-mounted bitx:

#define bfo_freq (11998260UL)? ?// Hz? ? replaced the similar statement in the base sketch

#define SI5351BX_XTAL 25004560? ? ? ? ? // Crystal freq in Hz? ? ? ? replaced the similar statement on the cyrstal freqquency

When I repowered the devices, I don't completely understand it but I ended up having to "calibrate" the lower and upper offsets and basically set them to? zero.? ? ?

Preliminary testing then showed that the radio was now right on frequency.? ??