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Re: FM receiver filters



Bob,
My point is that filter is not easily found in a 455 KHz center frequency.
ECS, Inc.  makes 30 KHz wide filters in 10.7 , 21.4 and 45 MHz center
frequencies in 2 and 4 pole. They are available from Digi-Key. 455 KHz is
reserved for narrow band applications. A post data filter will reduce the
wide band noise by limiting the data rate to the incoming data rate. This
works well as long as there are no other signals within the IF pass band of
the receiver. 
For digital signals Hi and Low comparators would give you a fast response
for AFC and would not require excessive preamble.

Art,
KC6UQH

-----Original Message-----
From: Bob Bruninga [mailto:bruninga@usna.edu] 
Sent: Wednesday, December 31, 2008 7:43 AM
To: kc6uqh@cox.net; 'Anthony Monteiro'; G0MRF@aol.com; amsat-bb@amsat.org
Subject: Re: [amsat-bb] Re: FM receiver filters

> I suggest you consider AFC. 
> Not enough demand for that wide a filter.

Won't work for packets, or at least would require a long TXD making packet
communicatiosn inefficient. 

As to rarity, only one filter in the whole world is needed and that is on
the uplink receiver.  This lets eveyrone on the ground use conventional rigs
without mods, and with minimal doppler uplink tracking.

Too many simple satellites are being built without considering the need for
a wider bandwidth receiver on the uplink.  The difficulties of such an
approach for users is very obvious on the ISS cross band repeater, which is
using a stock amateur transceiver with a 12 KHz wide receiver on the uplink,
which makes even 5 KHz step tuning on the uplink be out-of-bandwidth
splatter half the time.

This is not a complaint at all.  The ISS team is to be congratulated for
making the most of what they were able to get up there.  It just takes more
skill by users on the ground...

It is good to see this new UK project planning on a wider uplink RX filter.

Bob, Wb4APR

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