Steve Thompson wrote:
>
> Looking at the gain and efficiency figures, it is behaving normally for an
> amp where the collector load impedance is too high.
I don't know if this means anything, but a check of the impedance looking into
the coax feeding my antenna (which seems to work much better with the amp than
the dummy load) with an ancient Millen antenna bridge shows about 35 ohms. Of
course, there's reactance involved, so who knows.
> >My conclusion is that the impedance match provided by the output filter in
> the
> >amp to 50 ohms is not optimal, but whatever impedance it is seeing in the
> >antenna is transformed to something more comfortable for the transistors.
> Yep - although it's not just the filter - it's all the matching between the
> transistor terminal and the output connector.
>
> It appears that there are some versions that work ok, and at least one other
> that goes like yours. It might be that there was a production change of
> circuit or component type that messed things up. A change of material in the
> iron/ferrite cores would be a good candidate.
And there are plenty of such components; a transformer on each module board and
a combiner.
> Unfortunately, if the finished
> unit meets a minimum cw output spec., many manufacturers won't care about
> anything else :-( some don't even worry about the cw spec. :-(((
A point which I made before, however, is that if the amp can't produce 750 watts
CW for a short period, then an attempt to get 750w PEP on SSB will result in
distortion.
73,
Vic, K2VCO
Fresno CA
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