Frequency calibration on a lab #bfo #calibration #frequency
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Hi folks,
Assuming I have RF laboratory instruments available, what could be an ideal scenario to calibrate ubitx frequencies ? Would it work to set a RF generator to 10,000,500Hz and expect to receive 500Hz when the ubitx is tuned at 10MHz? Or would it be better to measure the clk2 frequency with a counter? 73 Rafael Pinto - PU1OWL |
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Hi Rafael
Pay attention to USB and LSB, in the ?BITX-V6 the CLK2 is fixed, while the CLK1 switches from about 57 MHz to about 37MHz according to the selection of the side band used.
The documentation released for the tarutures, not surprisingly (albeit a bit impirically) is based on the measurement of the BF to calibrate the BFO and on the zero beat for the calibration of the VFO.
If you have RF instrumentation, the BF measurement method is certainly valid for VFO calibration, therefore, set the frequency of the RF oscillator to exactly 10MHz, in the TEST menu choose the VFO calibration, do the zero beat with the VFO, move the RF oscillator at 10.001,500 KHz, read the output frequency from the speaker with a good frequency meter and correct the calibration to read exactly 1,500 Hz (I managed to center the frequency of the VFO within +/- 0.01-0 , 02 Hz) exit calibration and turn off the ?BITX, turn it back on and follow the instructions in the documentation to calibrate the BFO (to center the quartz filter) ... that's it.
73 de
IW4AJR Loris On Mon, Jan 4, 2021 at 03:58 PM, <rafaelgcpp@...> wrote:
Hi folks, ? -- |
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P.S. Rafael,?
the laboratory measurement of the BFO is a little more complex operation, you consider that CLK2 is fixed to receive the USB, so it must be 1.5 KHz lower than the center frequency of the quartz filter, considering again that it is impossible obtain perfect filters using a Ladder Filter with quartzes that have the same frequency and fixed capacitors, for the reason that the quartzes are slightly different from each to other and the capacitors have a factory tolerance, so the quartz filters will be different for each ?BITX sold,
A laboratory measurement method is to firsth obtain the attenuation curve of the filter using a network analyzer (using the two connectors for the additional CW filter) and find the two attenuation frequencies at -3dB; calculate the bandwidth and find the frequenzy of center of your filter; turn on the ?BITX and measure the CLK2 with a good frequency meter, calibrate the BFO frequency by fixing it as exactly as possible at a frequency equal to -1.5KHz with respect to the central frequency of the filter.
This should be the measurement method theoretically, but I have not used it, so I cannot guarantee the final effect of the sound in the loudspeaker, when you listen to a signal on the antenna.
73 de
IW4AJR Loris |
Rafael Pinto [PU1OWL]
Loris Bollina