[amsat-bb] duplexer used as a filter

Graham Shirville g.shirville at btinternet.com
Tue Jul 28 08:45:24 UTC 2015

If you have a preamp in the same "enclosure" then try to keep it powered 
24/7...this certainly helps reduce the condensation risk, and, as has been 
said before - always have a small drain hole at the lowest point of the 
whole thing!


-----Original Message----- 
From: Kevin M via AMSAT-BB
Sent: Tuesday, July 28, 2015 9:05 AM
To: amsat-bb at amsat.org
Subject: Re: [amsat-bb] duplexer used as a filter

> Resist any temptation to seal up every crack and crevice of the diplexer.

> be sure to leave a weep hole or a small gap perhaps where your cables come 
> in through the bottom so moisture can escape.

Cannot agree with the above enough... You NEVER want to try and seal it up 
completely; mostly because you can't. (the block of epoxy being the 
exception) Warm day, heat beating down on it, cool rain comes, case 
temperature drops quickly, air inside will condense and suck a hole in your 
weather seal. Now you have moist air trapped inside... no weep holes. It's 
the same reason you never seal both ends of hollow feedline.

Are you thinking of using preamps? Then I want to suggest you try TWO 
diplexers... one on each feedline before the preamps. The 'unused port' on 
each can be capped with a simple antenna connector and a 50 ohm 1/4 watt 
resistor across it. Now, need room for all that? How about a tactical gear 

I've found the black cases from MCM electronics (~$25) and antenna brackets 
at the hardware store (~$5):



It's just a suggestion... your mileage may vary, batteries not included, 
attempt at your own risk. =^)

73, Kevin N4UFO

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