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[TowerTalk] Testing traps for heating

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Subject: [TowerTalk] Testing traps for heating
From: (Tom Rauch)
Date: Sat, 15 Sep 2001 20:51:34 -0400
> The two types of traps I want to test are high inductance
> self-resonant types and the "standard" inductor/coax
> capacitor type.  All are parallel resonant in the 20, 30,
> 40, 80 meter bands.  Of course the 30m trap need not be
> tested to 1.5 kw.

I've been slack at getting my tests on my web page, but I've 
already done this.

> I'm thinking I could "feed" the trap-testing setup with
> a antenna tuner, with a trap connected in series with a
> dummy load in an off-resonant condition.  

You need to either have an accurate impedance measuring 
system, or series tune the trap with a negligible loss device like a 
vacuum capacitor and measure power loss. The problem you will 
have is the impedance will be different at each point, so any meter 
you are likely to have will not be calibrated correctly at both points.

You are facing the same problems people face when trying to 
measure tuner loss. It is a difficult problem without test gear.      
> For a parallel test I was thinking that I could hook the
> trap in parallel with another tuned circuit that would
> have taps for impedance matching for input/output.

.....and what would that do?

For the parallel test at resonance, you can simply treat the trap as 
a resistor and measure the voltage drop across the trap with a 
known current, or as part of a resistor divider or bridge circuit.

The problem here is your test fixture has to be very good.

High inductance self-resonant traps are good at the higher band, 
and stink on the lower band. Coaxial traps are bad on the higher 

Conventional traps out of transmitting caps and air wound inductors 
are by far best. They have significantly less performance if you use 
coaxial cable for the capacitor.
73, Tom W8JI 

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