[TowerTalk] Bazooka 1/4 wave balun

[Tom Rauch]

> If you can put it into a resonant circuit, then you can
measure Q by
> measuring 3dB points, turning the measurement problem into
one of
> accurately matching levels (at the two points), and
measuring frequency
> accurately (which is fairly easy).
>
> A resonant circuit with a Q of 500 at 14MHz would have a
3dB bandwidth of
> 28 kHz. The challenge would be accurately knowing when
you're really at
> 3dB. And, how would you couple in the power in a
consistent way? A single
> turn link coupling probably wouldn't cut it.

I don't think so.

The 3dB point method assumes you have a perfect lumped
capacitor whose reactance changes as calculated by formula
and the inductor does the same. Large components don't do
that, especially as we approach a frequency where the
components are changing fast. Far away from self-resonance
everything changes normally and with lumped components that
would work fine assuming you could measure 3dB points.

If I add stray capacitance across an inductor by using a
poor inductor design and place that inductor in a series
resonant circuit, 3dB BW becomes narrower while the Q based
on loss resistance is actually reduced!

Some of my  narrowest mobile antennas have the highest coil
ESR.

73 Tom