From: "Tony (remove \"_\" from email address)"
Subject: Re: balun
Date: Tue, 05 Nov 2002 10:53:00 +1000
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On Sun, 03 Nov 2002 14:40:49 GMT, shb*NO*SPAMemail@example.com (Si Ballenger)
>On Sun, 3 Nov 2002 11:00:34 -0000, "Jason Bell"
>>Does anyone know of any sites with a simple balun circuit.
>>I only want to use it for video/audio over cat5 cable.
>>Many thanks Jase
>You can buy them for ~$25 each if needed. You might also try the
>baluns used for coupling coax to cat5 (~$5 each). The only design
>info I've seen mentioned using torodial (sp?) transformers, with
>the leads switched so that the lines are hard connected through
>the transformer. You might find the info doing a google search.
The "video baluns" I bought recently had so little inductance the picture got
really distorted (Fc about 5kHz instead of 50Hz or so). I'd like to find a good
source, but so far no luck.
A 1:1 transformer can be connected as either a "transformer" or a "common mode
choke", with similar results at HF (ie, bioth limited by the leakage
inductance). But at LF, the "transformer" connection gets better for isolation
and worse for signal propagation, whereas the "common mode choke" connection is
the opposite. Both video and audio need good LF signal response whereas just
about any electronically balanced circuit can avoid common mode noise at low
frequencies, so for MOST applications, the "common mode choke" connection is the
way to go.
The transformer needs to have the highest mu core available (F10?), and layered
windings - about 20 ohms per winding won't do anything too bad for any
application. You can even wind on multiple windings (eg 8 windings for 4
balanced audio channels over RJ45). Finally, interleaving parallelled common
windings between signal windings will reduce inductance further, for better HF