Quote:
Originally Posted by dmfdmf
Right, but if you've got any kind of Yagi with a horizontal boom it has the same problem, the wire leads are too short to drop the balun out of the way so it interferes with reception.
Yes, you have a difficult case. In these situations I like to say "every dB counts" because with such low margins and poor signals you never know if you are an iota of dB from a decent pic to an unwatchable one.
Agreed. I wasn't recommending the RCA751 for you, just the twin-lead extension trick that probably applies to any horizontal boom antenna and might wring out a few more dB in "extreme" cases like yours.
I have not analyzed your case closely enough, nor do I have the experience to help with your antenna selection.
I didn't really need to twist it as the extension was only 24" long to the j-pole and from there its coax. I'd be afraid of putting torque on the spade connectors where the balun attaches to the antenna if I twisted it. I am aware of the 1T/ft rule of thumb for twin lead but I thought that applied to long runs along the roof or down a 30ft mast. The twist keeps it from picking up stray RF signals. I don't recommend twin-lead running down the mast. Its hard to work with because you need the twists plus it can't be too close to metal so you need standoffs, etc. People switched to coax because its so much easier to work with. I think the gain in performance that I saw, which was rather dramatic for a system that was already working well, was probably due to soldered connectors (rather than crimped) and getting the balun away from the active elements of the antenna. If you go this route I'd be curious if it helps.
I'd also be curious if the method can be used on the one of those flat, vertical UHF antennas and if it would make any difference. I think the RF principle are the same -- get the wire away from the antenna, 90deg being the most direct method. But now your twin-lead drop line has to run along the front of the antenna at least 4-5" away from the mast, so you'd need to secure it with some kind of plastic standoffs and you'd need to twist it if its longer than a couple of feet. Once it clears the lower elements of the antenna, you could terminate into a balun and then run coax the rest of the way. This is a real world test I'd love to see.
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I'm interested in trying this but my radioshack only sells twin lead in 100 foot rolls, if I can find it by the foot it will be on my to do list. As for trying it on a flat uhf mine is out since it uses a pcb balum which is a true 1 to 1 75ohm connection. Thanks for the tip!