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[Discuss-gnuradio] Weird Behavior of BPSK on RFX 2400

From: Shyamnath
Subject: [Discuss-gnuradio] Weird Behavior of BPSK on RFX 2400
Date: Mon, 13 Aug 2007 18:18:00 -0700 (PDT)

Hi guys,
I am trying to analyze the functionality of each of the blocks in the dbpsk
mod/demod when I noticed the following behavior.

The high level modulator flow control is as  | Symbols |-> | RRC filter | 
-> |amplifier | -> channel
and that for the demodulator is               channel -> | Pre-scaler| ->
|agc| -> |RRC | -> |clock recovery| -> |slicer|

My understanding is that the real part of the output of the clock recovery
must be close to that of the symbols or some scaled version of it(+a, -a in
case of bpsk).

However, my observations (in the link below) show that the output of the
clock recovery depends a lot on the bit pattern, i.e., for the bit pattern
1010 the peaks of the 1s and the 0s are way smaller than those of the bit
pattern 1111110000.


Since we are using a RRC I would doubt it is due to ISI . and since the
radios are close to each other and there is a direct LOS I donot think this
is due to multi-path (or is it?). Is this  behavior due to some component on
RFX 2400/USRP or something else?

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