[TowerTalk] RF Inquiry HI-Q Filter CF5KV

[Rob Atkinson, K5UJ]

I think these are typically a PVC pipe with uhf females on the ends, between 
them around 10 or 12 inches of small 50 ohm coax with teflon dielectric and 
beads strung on it.  they are aka 1:1 ununs, common mode filters, and line 
isolators.  they stuff foam into the pipe so the beads don't clack together 
and break.  that unfortunately also holds in heat.   so you can make one 
without too much trouble and i would leave off the foam and pvc, but it 
might wind up costing more to make it than to buy it (well, not the RF 
Inquiry ones).
The chief advantage to making one is you get to design it to do well, what 
you want it to do.
My experience with the mfrd. ones for example is their attenuation begins to 
rapidly fall off below 7 mhz.  they do not do all that well on 75 m. and are 
transparent at 160.  if you want one to work on 3.5 and 1.8 mhz you could 
make one with mix 77 beads but it might be cheaper to wind 20-30 turns of 
coax on a paint bucket or garbage can.

rob/k5uj

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