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180: Difference between revisions
Added OCXO cal procedure details
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by attaching a small antenna to deliberately interfere with the national time standard broadcast, | by attaching a small antenna to deliberately interfere with the national time standard broadcast, | ||
and observing the interference with a communication receiver. | and observing the interference with a communication receiver. | ||
The method is to zero-beat the WWV standard frequency broadcast with the internal crystal oscillator to align the OCXO frequency. | |||
First tune ham receiver to WWV broadcast - say 10MHz - and watch the audio subtone using an oscilloscope connected to the audio out of the receiver. | |||
Then wait for specific minutes of the hour where there is no audio subtone in WWV. | |||
Then select 1μs output on 180A, which will have 10MHz as the harmonic. Connect a wire from the output of 180A as an antenna and couple it to the antenna input of the receiver. This way the 10MHz WWV and 10MHz harmonic from the 180A, will beat in the receiver input. The difference will be visible as a wave in the oscilloscope. Then adjust C105 to align crystal frequency as close to the reference WWV 10MHz, that the frequency difference becomes zero or the waveform on the scope becomes flat. | |||
You could also use the S-Meter in the receiver instead of the oscilloscope to perform the same. | |||
The Tektronix 180 has toggle switches. The 180A has pushbutton switches. | The Tektronix 180 has toggle switches. The 180A has pushbutton switches. | ||