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[TowerTalk] RF Inquiry HI-Q Filter CF5KV

To: towertalk@contesting.com
Subject: [TowerTalk] RF Inquiry HI-Q Filter CF5KV
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
Date: Mon, 21 Feb 2005 15:35:20 +0000
List-post: <mailto:towertalk@contesting.com>
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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