Quote:
Originally Posted by pips
...my intent is to build 4 sbgh with no reflector and stack vertical down the mast on top of a 50 foot tower.i will use pieces of pvc pipe to shield the twin line where possible.
|
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.
Quote:
|
...my question now is can i use and off the shelf baulen (4 to 1) or a (1 to 1)?
|
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.
----------------------------
Balun: A device that can convert (efficiently mate) a balanced transmission line (twin lead) to an unbalanced transmission line (coaxial cable).
.