Gnuradio

GNU Radio
1

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!

2

On Tue, May 3, 2011 at 2:07 PM, Mantas Juskauskas
[email protected]wrote:

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