Anyone ever use a 4:1 TV Balun? - HomeBrew Forum at eHam.net

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eHam.net Forum : HomeBrew : Anyone ever use a 4:1 TV Balun?

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Anyone ever use a 4:1 TV Balun?	Reply
by KI6LNG on November 2, 2009	Mail this to a friend!
I set up a 20 meter folded dipole fed with coax. I don't have a 4:1 balun to transition from the coax tot he antenna, so I put up a TV balun with the appropriate adapters. Has anyone ever used one of these before in amature radio? I know it's probably not safe to transmit with, but receiving seems to work great and no SWR problems.

RE: Anyone ever use a 4:1 TV Balun?	Reply
by N2EY on November 2, 2009	Mail this to a friend!
It depends on the balun... Some of those TV baluns will go down to 5 MHz or so, which makes them useful at HF. Others start cutting off just below old analog TV channel 2, making them useless at HF - but which made them useful in TVI reduction caused by fundamental overload. For HF receive-only use with a dipole, you don't really need a balun. 73 de Jim, N2EY

RE: Anyone ever use a 4:1 TV Balun?	Reply
by KI6LNG on November 2, 2009	Mail this to a friend!
What makes them cut-off below a certain frequency? Is it the diameter of the wire used inside? How many watts do you think it can handle transmitting?

RE: Anyone ever use a 4:1 TV Balun?	Reply
by WB2WIK on November 2, 2009	Mail this to a friend!
What makes them "roll off" below a certain frequency is they don't have enough turns of wire to act as an effective transformer below a certain frequency. Most of the ones I've used roll off a lot below 50 MHz or so, as they don't need to work below that. The ones I have will handle about 1 Watt transmitting power...maybe a bit more. I did "blow one up" by using it with a 5W 2m hand-held, but I didn't really expect it to handle 5W, anyway! In their normal application it's rare for them to ever need to handle more than 10 milliwatts.

RE: Anyone ever use a 4:1 TV Balun?	Reply
by WB6BYU on November 2, 2009	Mail this to a friend!
A friend of mine uses several of them with a delta match on his VHF yagis, but those are used for receiving rather than transmitting. I do remember also using two of them in series with a high pass filter to keep HF RF out of a cable TV lead, only to discover that the transformers themselves provided sufficient cutoff at the low end of the band that the filter between them wasn't needed. But that does depend on the specific model - some are rated down to 5 MHz, others (often with no stated rating) only to 30 or 50 MHz. And, of course, it isn't a sharp cutoff, so it depends how much performance degradation you are willing to tolerate. However, for a folded dipole on 20m you could use an electrical quarter wave of 150 ohm feedline made from two 75 ohm coax sections in parallel to step it down to 75 ohms - giving the same effect as the balun, but capable of handling your transmitter power.

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