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Re: [TowerTalk] "bias Tee" from MFJ and others

To: K4SAV <>,
Subject: Re: [TowerTalk] "bias Tee" from MFJ and others
From: Jim Lux <>
Date: Thu, 07 Sep 2006 11:00:11 -0700
List-post: <>
At 08:34 AM 9/7/2006, K4SAV wrote:
>They are very simple as you expected.  The design process is straight
>forward.  It's just a capacitor in series with the coax line, and an
>inductor connected to the center line, and on the other end of the
>inductor the dc is injected. There is a bypass capacitor to ground at
>the point where the dc is injected. You need two of these circuits, one
>at each end.
><snip of useful design details>
>Jerry, K4SAV

My question is two fold:

1) what practical experience have people had with them, particularly 
in terms of interactions with other widgets (i.e. transient 
suppressors).  The Ameritron remote antenna switches we have at W6VIO 
are incompatible with the transient suppressors we have, because the 
transient suppressor has a DC path to ground, which shorts out the 
control signal.

2) What about NEC issues (class 2 power wiring and the like)?

3) Of the commercially available parts, what's the pros and cons? For 
instance, SGC also sells a DC injector (bias T under another name) at 
roughly $100/pair. I've not found them yet in the Tessco catalog, but 
I'm sure they're there.  This is before I break down and build one myself.


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