Calibration of the High Stability VXO of WC2XSR/13
Calibration traceable to NTIS / WWV
The example shown here is for a carrier frequency of 166.500 KC, with the transmitter VXO operating at a frequency of 2664.000 KC.
** Begin Calibration Procedure**
1) Set the calibration variable frequency oscillator ( BC-221 VFO ) to a frequency of 2500 KC.
2) Hetrodyne the 2500 KC signal from the VFO with the 10,000 KC signal from WWV.
3) Achieve zero beat between the VFO signal and WWV by watching the S-meter on the receiver while simultaneously adjusting the VFO for an "S" meter swing of less than 1 cycle per second.
Since we are comparing the fourth harmonic of the VFO to WWV, this indicates an accuracy of +/- 1/4 Hz of the 2500 KC VFO fundamental frequency.
4) If necessary, adjust the time base oscillator of the frequency counter to make the frequency counter indicate a frequency of 2500.000 KC.
Since the counter's stated accuracy is +/- 1 count, we may assume that the indicated reading shown is accurate to +/- 1 Hz. In practice, a time-averaged series of readings will allow us to get thet uncertainty down to about 1/2 Hz, by simply observing how often the indicated reading is over or under the expected frequency.
5 ) Measure the WC2XSR VXO carrier oscillator frequency with the frequency counter. Adjust the VXO to read 2664.000 KHz.
** End Calibration Procedure**
We know that the frequency counter is accurate to within +/- 1 Hz, therefore, we also know the VXO frequency to within +/- 1 HZ or better, depending on the accuracy of our time averaging measurements.
Since the 2664 KC VXO signal is divided by 16 to obtain the actual 166.5 KC carrier frequency, we can also conclude that we know the carrier frequency to within +/- 1/16 Hz, or better, depending on the accuracy of our time averaging measurements.
This places the carrier of WC2XSR between the upper and lower limits of 166.49994 to 166.50006 KC.
Since the VXO stability is generally within +/- 1 Hz over a 24 hour period, we can conclude that the carrier frequency will remain within 1/16 Hz of 166.500 KC.
73, Ralph W5JGV
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