[Elecraft] high ref warning

[Ron D'Eau Claire]

Ken W8OB wrote:
I just noticed while running 100 watts output on 10 m ssb that voice
peaks or a whistle will sometimes give me a high reflected warning. The
vswr on the antenna is 1.3 to 1 where I was operating and I noticed what
looked to be a bit of oscillation also. Anyone else run it this? I have
the station gear well grounded to a separate rf only ground here. I
could not get the problem to duplicate on other bands only ten meters
==========================

The first thing to do is to run the amp at 100 watts output into a dummy
load and see if the problem goes away. That will ensure the problem is
in the antennas system and not in the amp. 

One very common reason for this behavior is an antenna system with a
toroidal balun. If the toroid is not big enough to handle the magnetic
flux, it will saturate causing a big spike in the SWR on the line. This
will happen when the power level gets too high, producing too strong of
a current in the windings. Your SWR meter may not be quick enough to
show the jump in SWR, but the KPA100 SWR protection circuit may well be.


That's certainly not the ONLY reason for this to happen, but if you have
a toroid in the antenna system, it's a good bet. Especially if things
look fine at lower power levels.

Other reasons in the antenna system can be arcing. This can happen in
baluns too when the line is at a high impedance where the balun is
inserted. The turn-to-turn voltage may exceed the capabilities of the
insulation. Also, a marginal connection anywhere, or marginal insulation
anywhere in the feeder or at the high-impedance points of the antenna
can cause this behavior. 

Ron AC7AC
K2 # 1289