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RE: Echo TNC




The SDR-1000 PLUS a very good sound card indeed.  We are finding out
now how good.  The issue is that there are many cards coming on the
market now that support sampling rates that are more than sufficient to
do wider band FSK, and other things, probably almost to 100 kbps.
Unfortunately, almost all of these sound cards have a FIXED
antialiasing filter that renders the faster sampling rates useless
above the cut off for these filters which is typically around 20000 Hz
(some slightly higher).  The ones that do not have this limitation
cost almost as much as the SDR-1000 board set or HIGHER.  We will
be able to up to 20 Kbps with the standard sound cards but we want
more.

I am still looking as I would not want to have to recommend the
Lynx L22 ($900) as the only viable sound card.

For this operation,  a different approach might be preferable.
We might want to use some of the boards described in this forum
earlier where a wider bandwidth A/D D/A are on a board and this
is following by software running on an FPGA to do what is called
CIC filtering to downsample and get processing gain. Since ECHO
will not be a weak signal satellite by any stretch, this approach
might be preferable.  This is all TBD as we go forward and
attempt to support these higher data rates.  I wish I could be
more definitive but that is where I am now. I have a meeting with
others about this issue and others next week.  We'll see how it
goes.

Bob
N4HY



-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Stan
Sent: Monday, May 10, 2004 6:58 PM
To: Bruce Snyder
Cc: Amsat-bb
Subject: Re: [amsat-bb] Echo TNC


Hello Bruce and the Net:

Reportedly the SDR-1000 transceiver (with optional transverters) will be 
compatible with ECHO.
SDR-1000 is the software defined radio and with optional DEMI  2M 
transverter/PA  and a 436 MHz transverter/PA.
it will be able to downconverter to the 11 KHz  I/Q (dual) channels for 
a soundcard/PC processing under windows.


Stan, WA1ECF



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