[aprssig] diplexer/duplexers for APRS

Keith Kotch kkotch at earthlink.net
Tue Sep 6 19:48:30 CDT 2005

It seems like the "simple" idea I was trying to find a solution for is being
thought of in a more sophisticated manner.

I don't care if one radio or side of the equation is temporarily blocked, in
fact, that is exactly what I was thinking.

How does the circuitry in a dual-band dual-receive radio work, say the D700,
when everything is connected to 1 antenna? 

Radio 1 is a dual-band, radio 2 is a 2m packet radio all connected to 1
dual-band antenna.  Both sides of the dual-band and the packet radio can
receive at the same time.  It's only when one of the three transmits,
(actually it would be when one of the two radios transmits) that the others
need to have the rf blocked.  When the packet radio transmits, the signal is
blocked from backfeeding through the coax to the other radio.  When the
dual-band transmits the internal duplexer there protects one side and the
external duplexer circuit protects the packet radio.

If it can be done in any dual-band, dual-receive radio, why can't it be done
outside the radio?

Keith, KF4BXT

-----Original Message-----
From: aprssig-bounces at lists.tapr.org [mailto:aprssig-bounces at lists.tapr.org]
On Behalf Of Jim Lux
Sent: Tuesday, September 06, 2005 8:18 PM
To: aprssig at lists.tapr.org
Subject: [aprssig] diplexer/duplexers for APRS

It occurs to me that since APRS is a single frequency kind of operation, 
you might be able to get a SAW filter made that just passes 25kHz around 
144.39, and another that rejects the 25kHz around that same frequency 
(actually, it might be the same filter).

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