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Old 25-Jul-2014, 4:00 AM   #5
pips
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Join Date: Jul 2014
Posts: 20
Quote:
Originally Posted by tripelo View Post
You probably know that PVC only shields twin lead from the weather, it does not electrically shield it. PVC is a lossy dielectric at UHF frequencies, I would not use it continuously close to twin lead, probably OK if using it for spacers something like a standoff insulator, with no continuous exposure.



Off-the-shelf baluns are normally transformers and baluns combined. The 4 to 1 indicates a transformation ratio (i.e. 300 to 75 Ohms). If you use a parallel combination that yields 75 Ohms then you do not need a transformer, only a balun, a 1 to 1 balun.

Any commercial 4 to 1 balun that I have measured (many of them) will have substantial loss at UHF frequencies, ~1 dB or usually more. A ferrite choke balun can be made to have losses below a few tenths of a dB.

I do not know of any commercial 1:1 baluns. They can be made to look like a transformer, or they can be the 'ferrite choke' version.

If you should find a combination of antennas that yield 300 Ohms impedance, a 'half-wave loop' balun provides about the lowest loss.

If your transformation ratio is anything other than 4 to 1 or 1 to 1, you will need to do some more research. Odd ratio baluns or balun/transformers can be made, but most would not attempt. In such a case, probably the best approach would be to transform the non-standard impedance to either 75 or 300 Ohms, then use an appropriate balun. The transformation could be done with custom-made transmission lines and lengths.

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Balun: A device that can convert (efficiently mate) a balanced transmission line (twin lead) to an unbalanced transmission line (coaxial cable).

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hmmm now u got me thinkin.i could go into 300 ohm wiring on antenna then twin lead to the tv and convert at that point or i could do balun and if i read it right i can do clamp on choke then to tv.so many options.i do believe stacking with the twin lead is the best way to start its just getting from tower to tv
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