I have a Diamond HFV-5 (rotatable dipole) in the attic fed by ~30ft of coax. The antenna system comes with a Balun at the feedpoint. Would it be worthwhile to add an inline RF Choke (Unun) in addition or is that covered by the Balun?



A balun effectively allows you to connect a balanced antenna (such as a dipole) to an unbalanced feeder (such as coax). You have a balun at the feed point of the antenna, with a coax socket on it, which means that the feeder going from the radio to the antenna is unbalanced.

The HFV-5 is an antenna that presents a 50Ω impedance on its coax socket and it already has a balun. Your radio's impedance at the antenna socket is presumably also 50Ω, and I am assuming that you are using 50Ω coax as the feeder.

I am puzzled as to what good the unun would do in this system.

(So to answer your question - I don't think it would be worthwhile to put an unun in addition to what you already have).

  • $\begingroup$ Thanks. I got the idea after I had a problem with a computer monitor turning off when transmitting on 20m (related to power supply). I was asked if I had a choke, but I assumed the balun that came with antenna would suffice. $\endgroup$ – Inisheer Oct 8 '19 at 2:33
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    $\begingroup$ You assumed correctly. I have an HFV-5 not 10 feet from my computer screen, and don't have any problems with RF in the shack. I get more problems with computer noise getting into the antenna itself :) $\endgroup$ – Scott Earle Oct 8 '19 at 2:34
  • $\begingroup$ Ok, thanks. Good to know you have the same antenna! de W0CD $\endgroup$ – Inisheer Oct 8 '19 at 2:37
  • $\begingroup$ And you have the same antenna as HS0ZLW! :) $\endgroup$ – Scott Earle Oct 8 '19 at 2:41

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