Quote:
Originally Posted by GMB
Yes, that's the impedance match. But it may need a balan too.
I have seen aerials that skate over this issue and hope no-one will notice.
A crude half-wave dipole will match 75 ohm nicely, but needs a balun to match coax.
At VHF you can use a ferrite clamp or just make a few loops of feeder near the aerial to be the balun.
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I wonder if 75R-to-75R receiving baluns form domestic applications are available commercially. Back in the 1950s, when 75R twin feeder was used to some extent, Belling & Lee at least used to offer them, but I should imagine that they faded out as stock items from the major aerial manufacturers. On the other hand, I think it likely that FM aerials have used folded dipoles for many, many years, in which case the (readily available) 300R-to-75R balun might be more appropriate. Professional versions are available, e.g.:
http://www.nhsignal.com/pdf/products...al-purpose.pdf.
The transformer type seems simple enough to make, though, as shown in the attached excerpt from King, Practical Aerial Handbook.
Cheers,