Coax, Baluns, and Twinlead

[johnnymitch74]

Hey all.
I'm looking to use 300 ohm twinlead as an alternative to 50 ohm coax for my antenna because I need long lengths that end up being very costly in terms of RG-8 or LM-400 coax and I want the low loss. What I'm looking for is a balun to transfer the 300 ohm impedance of the twinlead to the 50 ohm impedance of my receiver connector. does such a thing exist? or could I use a 300 to 75 ohm balun, and then a 75 to 50 ohm one? what type of loss figures would I be looking at here? obviously I need a piece of coax to connect to my receiver.

Thanks!

 

[prcguy]

What frequency range? TV baluns are designed for about 50 to 800MHz but they can have several dB loss at some freqs across that range.
prcguy

 

[n5ims]

Instead of going through all of that trouble, just use a good grade of RG-6 for your coax. It's designed for low loss over the TV frequency range, which covers what most scanner listeners want and is low cost and easy to install. You can get adapters from the standard F connector they normally use to match what your antenna and scanner would need pretty easily and they even make many types of connectors (including the BNC many scanners use) to install directly on the coax. RG-6 is also well shielded so you'll have less chance of unwanted signals being picked up by it (especially over twinlead) by having it run near or cross other cables.

Just how long of a run is it going to be? Length = Loss so the shorter the better, especially at higher frequencies! For scanner use, loss per 100 foot at the highest desired frequency is much more important than impedance so using the 75 ohm coax won't be an issue.

 

[mpddigital]

Question, what do you mean by "long lengths"? If it's 100ft or so go with some RG-11 and get a great signal at low cost. You should be able to pick it up for 25 cents a foot or so.

 

[kb2vxa]

300 ohm twin lead isn't exactly 300 ohms so you have a bit of wiggle room here, especially considering the fact that antennas aren't exactly 50 ohms either and the receiver input can vary widely. This thing about impedance matching is WAY overrated especially when the real consideration is the construction quality and user treatment of the transmission line. When it comes down to it TV stuff is more than adequate so if you use "heavy duty" twin lead that will hold up to the elements for a good number of years and waterproof everything outdoors a couple of baluns, adapters and short TV coax jumpers to connect it all up will do you justice. Just don't run the twin lead in metallic conduit or under metal siding and you'll do OK.

All things considered twin lead and open wire lead (also available for TV use) especially have practically no loss as compared with the best coax and even hard line. That's why I say go with it if signal loss is a real issue especially at the higher frequencies, if not coax is certainly a whole lot easier to deal with.

 

[johnnymitch74]

Okay yeah i'll probably just go with RG-6 then. My lengths will probably be 50-100ft and i'm mainly monitoring rail band (160mHz) and 440 band stuff. Will the losses be minimal here?