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?
1 Answer
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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).
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$\begingroup$ 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– Inisheer2019-10-08 02:33:11 +00:00Commented Oct 8, 2019 at 2:33
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1$\begingroup$ 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$2019-10-08 02:34:55 +00:00Commented Oct 8, 2019 at 2:34
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$\begingroup$ Ok, thanks. Good to know you have the same antenna! de W0CD $\endgroup$Inisheer– Inisheer2019-10-08 02:37:18 +00:00Commented Oct 8, 2019 at 2:37
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$\begingroup$ And you have the same antenna as HS0ZLW! :) $\endgroup$2019-10-08 02:41:51 +00:00Commented Oct 8, 2019 at 2:41