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[aprssig] Re: aprssig Digest, Vol 15, Issue 8

Steve Noskowicz noskosteve at yahoo.com
Wed Sep 7 21:09:12 UTC 2005

Message: 14
Date: Mon, 5 Sep 2005 10:00:23 -0400
From: "Keith Kotch" 
Subject: [aprssig] Duplexer or Diplexer
To: "'TAPR APRS Mailing List'" 


Scenario: Dual-band mobile and separate 2m mobile with tnc. 

Can a duplexer/diplexer be built (or is one available) that would allow both
radio systems to be hooked up to one dual-band antenna? [...snippitty snip...]

Keith, KF4BXT




Diplexer/duplexers are basicaly the same thing.  They are _Frequency selective_ devices, also called filters.  If one transmitter is on 2M it will go through it's duplexer to the antenna _AND_ through the other duplexer to the other radio producing maximum smoke.



A bit more info.  IF, and that's a big if, you have $$ there are ways to combine things on the same antenna, but there are many considerations and restrictions...Mostly that you have to design the thing for specific frequencies only.  You can't Tx and Rx randomly.

Multi transmitters on one antenna? ...small to big problem.  

Multi receivers on one antenna? ...small to medium problem.

Both? ...time to drag out the stamp collection.  (:-)

However, the bottom line is that you can not have two radios connected to one antenna and have random Tx and Rx on random frequencies.  

With the APRS radio through a cavity (a big one-or several), very quiet radios (VCO sideband noise-wise), a broadband filter for the rest of the band with a notch on 144.39 and a good antenna system, it is probably possible, but the required cavities would probaly fill the powder room and more.

73, Steve, K;9'D.C,I

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