At 12:19 PM 7/11/2003 -0500, Sam Effinger wrote:
>Question: I am going to build a 1:1 balun and want to put in in a PVC
>pipe..the question is what can I fill the pipe with....I am thinking about
>filling the pvc pipe with that expandable foam that is used to fill cracks
>around doors etc.
>
>
>Is that stuff corrosive ...any heat concerns ??
The stuff's not corrosive, but it is a great thermal insulator, which is
bad in the usual bead balun, since the common mode energy is being
dissipated in the beads (or, alternately, reflected back by the open
circuit they present)
Why do you want to fill the pipe with anything (other than air?)...
Ideally, you want something that can carry the heat to the outside world,
or at least to the PVC pipe. Transformer (mineral) oil would be good,
because it will circulate as it gets warmed, but check the compatibility
with your coax jacket material and the beads.
The next best thing would be to size your PVC so that it is a snug fit to
the beads.
You could use the foam to hold the coax in place (essentially as a cap),
but other stuff might work better (epoxy, silicone, etc.)
If you really want to pot the thing, you want to choose a potting material
that has reasonably good thermal conductivity (which is where foam is
terrible), and that has a thermal expansion coefficient that reasonably
matches the ferrites (so it doesn't break apart slowly as it temperature
cycles every day).
The usual plastics vendors (GE, Silpak, etc.) can advise you on potting
materials.
Jim, W6RMK
>I know some folks use it in the end of elements to seal the end and hold
>the rope in place..but will it work for the seal in a balun ???
>
>Glen K6NA makes the best baluns and uses epoxy ( he isn't making any at
>this time )...I don't want to buy all the epoxy as I only want to make a
>couple..
>
>any ideas ??
>
>
>Thanks for any help...
>
>Life is good....
>
>Sam K9SD
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
>any questions and ask for Sherman, W2FLA.
>
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