http://www.wa2ise.com/radios/twin_lead_j_pole.jpg
Except for the TV balun, this is your standard issue twinlead 2M Jpole antenna. Difference here is the use of the TV balun, and where that balun attaches to the antenna. TV baluns are 4:1, here it's a 200 ohm to 50 ohm. It connects to the Jpole at its 200 ohm impedance point, instead of the usual 50 ohm point. More importantly, the balun provides the Jpole a balanced feed, which is what it wants to see. And we avoid RF radiating off the coax cable. Easier and cheaper than ferrite beads and coiled coax. You'll need to get an F to BNC adapter, though. Or if you have some RG58 with a solid center conductor, and some screw on F connectors, you can connect the 50 ohm coax directly to the balun.

Built it and I get good results and good SWR too.

How much power you reckon one could transmit through that type of a balun?

How much power you reckon one could transmit through that type of a balun?

I've gotten about 10 watts thru one. But that's likely about as much as I could expect. These twinlead Jpoles are usually used with handhelds in hotel rooms when traveling.

For more power, you could get a bigger ferrite toroid (one good for VHF work), some ethernet cat5 twisted pair (balanced 100 ohm), and make your own 4:1 balun.

The main issue I have is that a F-connector is a 75-ohm connector where as a BNC is either 50 or 75...but you're still going to a 50 ohm transmission line. There would be an impedance mismatch in the F to BNC adapter...or should be.

Not that big a deal. 50 Ohm/75 Ohm mismatch is 1.5:1 VSWR and about .18 dB loss.

I was taught in Channel Master's CATV/MATV school that most 75/300 ohm baluns are actually 72/300 ohm - that they were designed to match the natural impedance of some antenna, I've forgotten which one - dipole?. The older CM 8281 baluns (75 - 300/300) for coax/F to VHF/UHF 300 were listed in the catalog as 72 ohms initially, but Winegard, Finco and Blonder-Tongue all used 75, so the assimilated.

So I guess any mismatch is even lower if they are indeed 72 ohm....