How many turns for a match using RG-6

[Oldglide]

I hate those cheezy consumer matching transformers. I want to build a 48"-18" OCFD. I want to use RG-6 without a matching transformer. How many turns of RG-6 around a 3/4" core would be required? I've read differences of 6-10 turns. Is this even feasible? Is there a formula to figure this out?

 

[prcguy]

Winding coax around a ferrite core will only make a 1:1 choke balun. There are various ways to make a 4:1 balun but it involves winding a specific amount of turns around a specific core type for the frequency range you are using, then interfacing coax to that.

At VHF/UHF this becomes a very precise operation and I doubt you could make a 4:1 balun good to 800MHz range unless you used the exact same methods as the TV transformer mfrs using a tiny ferrite bead and # 30 wire. For use through around 500MHz a small binocular core of maybe #43 ferrite material would probably work out.

Bottom line, a 75 to 300ohm TV transformer ain't so bad, especially when they cost 99c.
prcguy

 

[N_Jay]

Note, some cheap TV "balun"s are not true balun transformers and are more un-un, Some also have DC continuity.

Have fun, but as said, I doubt you can do better building a wide band transformer yourself.

 

[Fred1]

18by 48 OCD

I have made one out of an old rat shack scanner ant. The old one that had 3 element and r radials about 36 inches. Works good 27mhz to 800Mhz. I used a radios shack tv balun with RG6 works good. Total cost about 26 bucks. I prefer the 18 inches on top. Ant is up about 30ft from ground. 1/2 inch cooper pipe would be better.