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Re: [Discuss-gnuradio] Question about LFTX and RFTX

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] Question about LFTX and RFTX
Date: Tue, 07 Aug 2007 13:27:19 -0700
User-agent: Thunderbird (X11/20070604)

Ismail Mohamed wrote:

> My question is, with the LFTX/RX boards, is the communication truly
> baseband such that frequency synchronisation can be totally ignored?

Not quite.

With the LFTX/RX boards, DC does indeed remain DC at the other end.
However, the crystals in each USRP still govern the sampling rate, and
each can be up to 50 PPM off (new USRP hardware has 20 PPM spec'd
crystals now.)

So the same issues with respect to symbol timing recovery exist.

In practice I've never encountered a USRP that had more than a few PPM
crystal offset--but you can only rely on the spec range, especially in
variable environments.

Johnathan Corgan
Corgan Enterprises LLC

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