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 .
Sent from my iPad 2
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