Re: [Discuss-gnuradio] Frequency Offsets in RFX 2400

[Johnathan Corgan]

On 1/9/08, shyamnath gollakota <address@hidden> wrote:

> Thanks a ton for the reply. My main concern is not that the frequency
> offset is high enough but that it changes pretty often (every time I run
> a new run) which makes it difficult for repeatability.

The frequency offset in the USRP is largely due to thermal transients
associated with either power cycling the unit, or periods of on-off
activity.

> So is there a way in software  where I can make sure that the frequency
> offset is constant either by finely controlling the center frequency at
> the tranmitter every time I run or is there some other way around this
> problem?

Frequency tracking/synchronization is often the most complex (read,
fun :) part of receiver design.  Depending on your modulation type,
there are a variety of phase-locked loop architectures that can fine
tune the center frequency of your signal.  Simplified, you calculate
an error value based on some property of your received signal, then
use that to nudge the center frequency up or down until the error
value goes to zero.

-- 
Johnathan Corgan
Corgan Enterprises LLC
http://corganenterprises.com/