[TowerTalk] Bazooka 1/4 wave balun

[Peter Chadwick]

The resonance method is probably the best, but you have to be a long way
from the self resonant frequency of the coil.


If you're below about 0.8 of the SRF, the apparent resistance =
Ractual/(1-ye2)e2
and Lapparent = Lactual /(1-ye2)

where y is the frequency of operation/self resonant freq

e2 means squared.


Hartshorn's Radio Frequency Measurements By Bridge and Resonance Methods,
Chapman and Hall, London, 1940

is good on this.

But getting a Q of 500 isn't easy, anyway. I have got a Q of 350 on a coil
wound with bunched conductors at 2MHz. A length of Air Dux was almost as
good, and would be better at higher frequencies.

I use the resonance method by coupling in very loosely with a 1 turn loop,
and a VTVM which has a 300Kohm input resistance according to the
manufacturer at 30MHz. That limits the Q you can have. But the capacitor Q
needs thinking about, too.

73

Peter G3RZP