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Re: [Discuss-gnuradio] questions about USRP2 sink block and upconversion

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] questions about USRP2 sink block and upconversion
Date: Wed, 03 Nov 2010 17:54:10 -0400
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On 11/03/2010 05:27 PM, Dan Harasty wrote:
> Marcus wrote:
>> It's usual in telecom systems for there to be some kind of AFC on the
>> receive side to compensate for transmit-side frequency error.
> Can't this problem also be solved with a transmit-side correction?
> If the "error" in this particular USPR2 LO is about 900MHz -
> 899.99701MHz = 0.00299 MHz, then won't telling the USPR2 to modulate
> to 900.00299 MHz pretty much get the tones to the right place?
> I imagine the correction will change with device temperature and age,
> and also by intended "center frequency".
> But as a first cut, won't that work?
Well, sure, you could "correct" the tx-side, but since the Tx has no way
of knowing how bad
  the Rx side is "out", it's better for the Rx side to use something
like AFC, and just let the
  Tx "do whatever it's going to do".

Particularly when there's more than one Tx/Rx pair.

Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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