On Tue, May 3, 2011 at 2:07 PM, Mantas Juskauskas <[email protected]>wrote:
> Hello, > > I am recently working with gnuradio's tx_samples.cc and USRP2. I have input > files that are .sc type, which are written and saved on Matlab. I have a > question though. > I've noticed that signals in the input files before being saved to .sc type > are being scaled, for example: > > signal = sin(A); > scale = 10000; > > new_signal = signal*scale; > > frwite(...) > > Why do we need to use this scaling factor? > > Thanks! > This is a result of the change from float to fixed point representation as the signals are sent over the wire. When using the tx_samples program, it's assuming shorts (16 bit I&Q), but this means that if you send a 1.0, it becomes a 1 out of a scale of +-32k. The copier here doesn't do any scaling (unlike the tx_32fc transmit function, which does the scaling for you). Tom
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