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Can the Keysight 8922's front panel DEMODULATION OUT; DATA, CLOCK and VALID connectors, be used to feed demodulated baseband data to an external 0.3GMSK signal generator to create a valid TCH burst?

The data cannot be used to feed a 0.3GMSK signal generator to create a valid TCH burst.

Here's why:

When a call is up on the air, the demodulated burst data from the timeslot the MS is assigned to is routed to the DEMODULATION OUT DATA connector. This signal is not continuous. It is only present after the assigned timeslot has been demodulated. The DSP has to find the midamble of the burst before it can decode the rest of the burst. This means that no demodulated data is available until the entire burst has been demodulated.

The DEMODULATION OUT VALID connector supplies a TTL level signal which is negative true during the time the data is being sent to the DEMODULATION OUT DATA connector. The demodulated burst data is clocked out of the DSP after the burst has been demodulated. The demodulated data clock rate is approximately four times the bit rate in the modulated burst, so the burst data is much shorter in time than the burst from which it was taken. The clock associated with this demodulated data is sent to the DEMODULATION OUT CLOCK connector.

The data has not been de-interleaved (in the channel codec) or decoded (in the speech codec). It is the raw digital data of the burst, it is not baseband data. Consequently the data cannot be used to feed a 0.3GMSK signal generator to create a valid TCH burst.