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

From: Thomas Tsou
Subject: Re: [Discuss-gnuradio] Weird Behavior of BPSK on RFX 2400
Date: Wed, 15 Aug 2007 15:00:40 -0400

In the clock recovery, the useful term in the output of the M&M error
detector becomes small for long sequences of identical symbols. This
affects the sampling instant, and I suspect is related to what you are
seeing. You can modify the gain_mu value to get these and similar


On 8/13/07, Shyamnath <address@hidden> wrote:
> 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.
>      http://nms.csail.mit.edu/~gshyam/data/clock.pdf
> 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?
> thanks
> Shyam
> --
> View this message in context: 
> http://www.nabble.com/Weird-Behavior-of-BPSK-on-RFX-2400-tf4264711.html#a12137123
> Sent from the GnuRadio mailing list archive at Nabble.com.
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