[Elecraft] KPA500 strange behavior

[W1IE]

Good morning,

I have an interesting problem in which I hope the group here has an easy
solution.

My KPA 500 is hooked to a TS-2000 outputting 20 watts to the KPA500 and
displays the following abnormalities :

1. At frequencies between 4581 kc to 4601.6 (we are working on MARS
frequencies) using USB and a waveform of M110A, the following
characteristics are observed.
2.  The amplifier stops transmitting briefly (less than a blink of an eye)
and then resumes during a M110A transmission at multiple random times. 
3. Does not appear to happen when using voice, although some stations on the
MARS net have mentioned that my transmissions sometimes do drop to very low
levels.
4. This drop out does not occur:
	a.  On frequencies outside the range as listed in item #1.
	b. If the emission is any other type other than USB/LSB.
	c. When I turn off the amplifier and only transmitting using the
TS2000 at 100watts.
5. Occasionally, but not every time when this event occurs I hear a relay
inside the KPA500 click
6. I did the following tests in an attempt to located the problem.
	a. The conditions occurs whether I am attached to any one of the
antennas I have here.
	b. It also occurs when a dummy load is attached.
	c. It still occurs when I switch out KAT500 antenna tuners (I have
two of them).




Initially, my thoughts were that the frequency range seems to lie some where
in the boundary between 3.5 and 5.0 band