[1000mp] Single band (80 meters) high swr problem

[1000mp@mailman.qth.net]

This is a followup to my initial query regarding odd behavior on 80 meters.

The problem is this. On 80 meters only (all other bands are fine) when
transmitting into an alpha 86a amp, without the internal tuner engaged,
there is a high swr indication that causes a power foldback which does not
allow the amp to be driven to full output.

Some additional data points since my first posting.

The problem is the same with both antenna ports A & B on the MP.

The rig seems ok in the ssb portion of the band, but the swr
problem gets worse the lower in the band I go.

Transmitting into a dummy load results in a flat swr and full output.

The problem exists with two different alpha 86a's, both of which work
fine with other rigs, and show no input swr problems with those rigs.

It looks to me like there is an out-of-band radiation problem with the
mp causing the high swr/low output problem.

Unfortunately, I don't have a spectrum analyzer to determine exact
frequency of the spurious radiation.

Placing an ICE bandpass filter inbetween the rig and the amp allows
full output.

Employing the internal antenna tuner allows the reactance to be tuned
out, resulting in full output.

While the later two situations provide bandaide solutions, they are
not dealing with the real problem which I would like to be able to
fix.

I suspect that playing with the line length between the rig/amp
my bring the swr down, but again, this appears to be just a coverup
for the real problem.

Any other suggestions as to what I should look for.

Have there been known failures of the bandpass filters? If so how
difficult are they to repair?

Thanks in advance.

cheers, Paul - VA7NT ex VE7CQK - email: paule@sfu.ca
"Those who hear not the music. . . think the dancers mad."