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Re: [Discuss-gnuradio] Re: transmission from usrp1 vs. usrp2

From: Lin HUANG
Subject: Re: [Discuss-gnuradio] Re: transmission from usrp1 vs. usrp2
Date: Wed, 12 Aug 2009 11:23:02 +0800

YES. I also found this fact that the dynamic ranges of two usrps are so different, just in these days.
Furthermore, the range of usrp.source_32fc is also +-1.0, right? Because I found the sample amplitude is very small when I use usrp2_fft.py observe the same RF input on USRP2, compared with usrp_fft.py on USRP.

2009/8/11, Johnathan Corgan <address@hidden>:
On Tue, 2009-08-11 at 09:38 -0600, Jordan J Riggs wrote:

> Here is the FFT output of the two devices.

This looks like gain compression or even clipping on the USRP2.

The dynamic range of samples to be sent to the usrp.sink_c block for the
USRP1 is +- 32767.

The dynamic range of samples to be sent to the usrp2.sink_32fc block for
the USRP2 is +-1.0.

In either case, the RFX boards go into gain compression in the upper 20
dB or so of their transmit range, so if you have a modulation which
requires linear frequency response (e.g., filtered BPSK), you need to
restrict the sample amplitude to +- 3000 or so for USRP1 and += 0.1 or
so for USRP2.

If you are in fact sending the same actual sample range valid for the
USRP1 (+-32767) into the USRP2 sink, you will of course get severe
distortion as the sink will clip this to a +-1.0 square wave.


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