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[Discuss-gnuradio] Freq. hop techniques

From: Steven Clark
Subject: [Discuss-gnuradio] Freq. hop techniques
Date: Tue, 2 Nov 2010 16:10:10 -0400

Hi all-

I got a simple form of frequency hopping working without too much trouble, by having a free-running flowgraph in thread A, while thread B periodically retunes the flowgraph's USRP output. This seems to work fine.

Now, what are some techniques to use if I want to introduce dead time to the transmission? In other words, I want something like:
Transmit at Freq 1 for 50ms
silent for 70ms
Transmit at Freq 2 for 50ms
silent for 70ms
Transmit at Freq 3 for 50ms

Should I make my flowgraph be "single-shot", and just restart it every transmit?
If I'm using a vector_source_b to provide input to the system, do I need to call rewind() prior to each flowgraph.start()?
If I'm using a file_source_b to provide input to the system, do I need to call seek(0,0) prior to each flowgraph.start()?
Or should I make the flowgraph continuous, but try to prevent any data from reaching the USRP during the dead time?
Should I use usrp_out.set_auto_tr(True), or should I manually toggle usrp_out.set_enable(True) and set_enable(False)?

How do I avoid usrp underruns ("uU"), if I am cutting off data from the USRP periodically?

How much tuning range do I have with the DDC alone? Is it +/- 32MHz? IE after I tune my daughtercard LO to 700MHz, I can tune from x to y solely with the DDC...what are x and y?

Thanks for any wisdom!


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