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Re: [TowerTalk] SWR Problem Balun or lightning protection?

To: Tony <>
Subject: Re: [TowerTalk] SWR Problem Balun or lightning protection?
From: Tod - ID <>
Date: Wed, 21 Dec 2011 08:50:00 -0700
List-post: <">>
This is an interesting thread which has gotten difficult to follow. 

Let me see if I understand it correctly.

1. When you transmit at high power either with a continuous carrier [ RTTY] or 
with a high transmit duty cycle the VSWR you observe changes and increases.

I have some questions that I would seek to answer if it happened at my station.

1. Is this something that I noticed only recently?
2. If the answer to (1) is yes, then how long ago do I think it was operating 

3. What has changed since I think it was operating correctly?
  a. New mode or method of operating?
  b. New equipment  - feed line, connectors, filters, relays, transformer balun 
, current balun, lightning protection, antenna tuner, amplifier, etc.
  c. The outside temperature is different than it was when it last was working 
correctly and the last time the temperature was the same as it is now the 
system was working.

If it was working and is now not working the cause should be associated with a 
change and that change should be somewhere in the collection of choices listed 
in (3) above.

Two years ago I experienced a similar phenomenon when operating on 160 meters. 
I mesured the change in VSWR as a function of time when I transmitted on air 
using a continuous RF carrier. I could observe the VSWR rising as the length of 
transmission increased. I could also see that the VSWR increased at a different 
rate when the temperature outside was 30 degrees F than when the temperature 
was 10 degrees F. 

The rate of VSWR rise changing with temperature led me to conclude that the 
cause was something outside rather than inside the shack. The fact that I had 
recently placed a trap in a top loading wire of the vertical was another 
change. The trap had been fabricated to handle very high voltages, but it 
simply was inadequate. The problem was dielectric heating of the coil form. The 
heat would  dissipate more rapidly when it was cold. I had to abandon that plan 
for my vertical.

I know that ferrites will heat when they are used in some high current 
situations. If the ferrite in your balun is being heated because you are 
operating with a higher transmit duty cycle that might cause what you observe. 
If there is a defect in the manufacture of the balun it might have failed or 
might never have been capable of what you wish it too do. In my case I tried an 
Unadilla trap but it too experienced dielectric heating my particular 
application. [ my application was not the one it was designed to handle]' 

Maybe something in the above will  help you resolve your problem .

Tod, K0TO

Sent from my iPad 2


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