Topband: 160 Meter BALUNS

[Tom Rauch]

<RG8X is a fancy name chosen for commercial reasons and is not an official
code for a qualified cable like other RGs.

I agree with that, except in practice I've used "RG8X" style cables for
nearly all my baluns (including some with very tight radius) below 20 meters
for many years without a single failure.

Since this is such a point of interest I'll make some measurements this week
and put photos of impedance sweeps (in Smith Chart format) up on a web page
so everyone can judge for themselves.

While most of the information is very good, I'd like to repeat a caution.
When you add a balun you are adding a series impedance to the line.

1.) There is no rule that says adding XX ohms will reduce radiation. It
actually might increase common mode so you have to judge the specific
application. Rules of thumb won't work. As a VE3 (sorry forgot the call)
pointed out 10,000 ohms might not be enough! 100 ohms might be too much! It
just depends.

3.) Watch out for low Q ferrites. The bulk of impedance in a 73 (or 75/77)
material bead balun is resistance that dissipates power. That's fine at low
voltage across the balun bead string, but not with modest or high voltages.

I'll put some examples up on my website, and include photos of actual
measurements.

By the way I just measured a 4" diameter 50 turn RG8X balun laying on the
ground and to my amazement the thing actually worked better! The series
resonances that caused the impedance dips above 13MHz W1JR alluded to
disappeared and the impedance over HF was quite high. It was significantly
better than a W2DU balun (which is significantly better than a W2AU balun).
No guarantee that repeats, but it is interesting.

73 Tom