[TenTec] Built in SWR meter bannans

[Rick - DJ0IP / NJ0IP]

Tnx agn Jim.

Our legal limit is 750w, but the wire I spoke of is only being used in
barefoot applications (100w).
For high power I use thicker 2mm Teflon-covered wire. AWG-12 is 2.05mm so
it's about AWG-12 that I'm using.

OK, I got the point on too little common mode impedance causing the damage,
but there is nothing wrong with using Teflon covered wire, is there?  

73
Rick, DJ0IP

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Jim Brown
Sent: Wednesday, April 24, 2013 1:39 AM
To: tentec at contesting.com
Subject: Re: [TenTec] Built in SWR meter bannans


Wrong change. Chokes fail because the common mode current is too high, and
that happens because their common mode choking impedance is too low.  Study
the discussion of chokes in my RFI tutorial.

>   What I
> typically use is a Teflon-coated twin-wire sourced locally with 0,75mm 
> diameter.  This would be about AWG-21. You don't even have to tape it 
> together.  For more power, then I use thicker Teflon insulated wire 
> and tape it together, which is work I totally detest.  That's the 
> hardest part of making a choke or balun.  And the special tape I 
> bought must be gold-plated; I paid 25 EURO ($30) for a tiny little 
> roll. (hi)

AWG #21 is quite under-rated for the current that can be present in a
transmission line carrying a legal limit transmitter.  #21 may be enough for
a 600 ohm line that is well matched, but not for a lower Z, and not if
there's mismatch.

73, Jim K9YC
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