Hi all
I have a Dentron MLA2500 linear, which mostly works fine, and I'm getting lots
of RF out.
However, on 3.5MHz (no other band) it is difficult to tune and was wondering
if someone could explain to me what is going on, and how I may cure the the
problem ? So here goes, remember this is just on 3.5MHz (80 M)
Prime mover is IC740
I tune the Dentron with about 10w from the IC740 into a Dummy load. When I have
peaked the linear, the SWR seen by the IC740 is around 1.8:1, as I increase the
drive, the SWR seen by the IC740 goes up to as much as 5:1 or more, thereby
reducing drive power. This slow cycling between lots of drive, but high SWR,
then the IC740 reducing drive (to protect the finals) reduces the SWR, the
power drops, and the whole thing starts again.
I have got a small ATU installed between the Linear and the Radio, but this is
not really curing the problem. My other HF radio (756ProII) with its Auto ATU
is a little better, but again it cycles.
Both Prime movers get to about 25 - 30 watts of drive and the cycling starts.
(Which means I only get about 250 - 300 watts out).
I know the Dentron doesn't have a tuned input, hence the small ATU between it
and the Prime mover.
I guess the amp is going into some form of hysteresis ? Perhaps I am wrong, but
some insight into whats happening would be good, and any suggestions as to how
to fix this annoying action would be great.
Thanks
Adrian MW1LCR
Wales
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