The modem 12.800000 MHz OCXO frequency reference accuracy is initially 0.1ppm. Over many, many years of operation it may drift slightly and should be re-adjusted to the nominal frequency.
Equipment needed:
Frequency counter with a minimum resolution of 0.1 ppm & a display of at least 8 digits.
Procedure:
- Connect the frequency counter to the QAM MODEM “TP” test point just above the “70 MHz OUT” SMA connector.
- From the top level of the front panel menu navigate to SYSTEM -> FACTORY CAL -> QAM MODEM -> OCXO.
- On the “OCXO-A Cal” screen, for a transmitter, do not change the “Mode”. For a receiver, toggle the “Mode” to “MASTER”.
- Adjust the “Freq Adj” parameter up or down one step at a time such that the measured frequency is 12.800000 MHz ± 1 Hz.
- For a transmitter, do not change the “Mode”. For a receiver, toggle the “Mode” to “SLAVE”.
- Exit the menus and SAVE the settings when asked.
- Disconnect the frequency counter.
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