Re: [Discuss-gnuradio] Demodulation of Intermittent QAM Signal

[Kyeong Su Shin]

Hello Ernest Fardin:

As you thought, synchronization loops in the PSK/QAM demod blocks may wander off if you input noise into those blocks.

I asked a same question before, and the answer was not to feed in any data to the QAM demod block when you think the transmitter is not on. I did not try this, but  maybe power squelch block can do the trick.

(Or, alternatively, maybe you can implement your own synchronization blocks and use a demod block that does not do synchronizations. I believe that you can use a constellation receiver block to do this.)

Regards,

Kyeong Su Shin

On Tue, Oct 17, 2017 at 10:46 PM, Ernest Fardin <address@hidden> wrote:

Hi,

I have a simple QAM16 loopback (Gray code, diff encoding, 4 sps) working as follows:

QAM Mod ---> Throttle ---> QAM Demod

This works fine if I have a constant signal level from the Tx. However, if I add a variable gain between the Tx and Rx and drop the Tx level to zero, then restore the Tx signal after a short time, the demod no longer works. I'm guessing a control loop inside the demod has wandered off during the interval with no signal. Is there any way to re-initialise the demod block to help it find its way again?

The objective is to simulate a 'bursty' link where the Tx is not permanently keyed.

Thanks in advance!

Ernest

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