[Amps] al-1500 parasitic?? or some other problem?

[Tom Rauch]

> What I am seeing is this... with the radio set for 14024.5 I tune the
> amp and all appears normal.  Except when going above about 800w a
> strong spur suddenly appears on 21036.9, almost exactly 1.5 times the
> transmitter frequency.  The spur can be moved by tuning the 20m radio.
> It is not moved by adjusting the tune or load controls on the amp. 
> With the amp tuned to 1500w output on 20m the spur can be turned on
> and off with fairly small adjustments of the amp tune control (5-10
> degrees max), it does not change over fairly large adjustments of the
> amp load control.  The onset point of the spur is not stable,
> sometimes it doesn't start until the amp is up to almost full power,
> sometimes when turning the tune control the start and stop points are
> not the same. But once started the spur is very stable and its
> frequency is not affected by the tune or load controls, not what I
> would expect from a parasitic.  

What do you have plugged into the receive antenna jack on the MP, 
anything? I've had problems with transceivers oscillating when using 
separate receive antennas because of poor external antenna port 
isolation. Those problems are very power level sensitive. 

It's also somewhat common for solid-state PAs are unstable running 
into narrow filters. Did you try removing the filter between the amp 
and the radio?

It's virtually impossible to be in the amp, unless you have a QSK 
board with bad components like low voltage breakdown in receive 
diodes.73, Tom W8JI
W8JI@contesting.com