[TowerTalk] Fair rite materials for choke baluns

[jimlux]

On 7/4/16 12:26 PM, Jim Brown wrote:
> On Mon,7/4/2016 12:01 PM, Jeff AC0C wrote:
>> The G3 data on the type 52 looks pretty good.  It sure seems like a
>> side by side bench test of the two materials would prove to be very
>> interesting.
>
> I'd be more interested in a study of power handling, which is a lot more
> difficult. A good starting point would be NEC modeling using the
> parallel equivalent circuit, which should give us a handle on the
> dissipation. Then subject the actual chokes to high common mode voltage
> to see how they hold up.
>
> An easy to build test fixture would be to use the choke as the end
> insulator of an end-fed center-fed dipole, as I've shown a couple of
> places, and shove high power at a high duty cycle into the dipole.

end-fed center-fed? What's that?  Do you mean coax into one side of UUT, 
then of the two leads on the other side, connect one to "half 
wavelength" of wire, and then what does the other side go to? The 
antenna support?  Or, since you're looking at common mode, both "output" 
wires of the choke go to the same place?

It seems one could come up with a test fixture that is a bit more 
compact (and repeatable) than a piece of wire in the air.

Looking at some data I happened to calculate for something else, it 
looks like a doublet that's a wavelength long has a feed point impedance 
of about 1000 ohms at resonance (where X is 0), but, the X goes from 
+500 to -500 pretty quickly, passing through zero.

(the magnitude of the R is going to be greatly affected by the diameter 
of the conductor).

I think what you want is some sort of tuner on the amplifier side (so 
you can get the power into the test setup) and then your choke and a 
suitable load resistor (several hundred ohms?).  if your choke has a Z 
of a few k ohms, you'll need a fair voltage on it to get any significant 
power to flow, but that's what a tuner might help with (or, maybe a 10:1 
turns ratio RF transformer that can handle hundreds of watts?)








That
> test hits the choke with rather high common mode voltage. Blast it for a
> while, then go feel it for heating and inspect it for any damage. The
> choke in question seems to be resonant in the range of 15-20 MHz, so a
> suitable dipole should be easy to rig.
>
> http://k9yc.com/VerticalDipole.pdf
>
> 73, Jim K9YC
>
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