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From: | Ernest Fardin |
Subject: | Re: [Discuss-gnuradio] Demodulation of Intermittent QAM Signal |
Date: | Thu, 19 Oct 2017 18:51:12 +1100 |
----- Original Message -----From:"Kyeong Su Shin" <address@hidden>To:"Ernest Fardin" <address@hidden>Cc:"GNURadio Discussion List" <address@hidden>Sent:Wed, 18 Oct 2017 15:11:50 -0700Subject:Re: [Discuss-gnuradio] Demodulation of Intermittent QAM SignalHello 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 ShinOn 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 DemodThis 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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