Jim
Very interesting, nice to have a man who knows his onions looking over the
circuit! My original design used a piece of thick screened multicore cable
for the transformer windings, primary was the screen, secondary was the
inner cores in series. This should have given my transformer very low
leakage inductance and it worked very well (and still does on my 2kW
version) into my LPF at 200kHz, which seemed to give a happy coincidence of
resonances. Incidentally I later discovered that the Ropex used exactly the
same filter values...! I had no problems with the low voltage version using
this construction, maybe I should have stuck to it with the high voltage
version but I worried about voltage rating of the cable.
I have always wondered about the decoupling of the centre tap, sometimes it
seems to help and sometimes it doesn't, all down to transformer construction
I suppose.
73
Dave G3YXM.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of James Moritz
Sent: 12 May 2004 12:19
To: [email protected]
Subject: LF: RE: G0MRF transmitter problems- investigations (long!)
Dear LF Group,
I built one of the G0MRF TX boards a few years back, with the intention of
using it for /P operation, but other things have prevented me doing that
yet... Reading about PA4VHF's problems persuaded me to try running my board
at full output. I found I had similar problems to the ones Dick describes -
the DC supply current was rather high, and components got hot, especially
the output transformer. Increasing the DC input to more than about 100W led
to things getting excessively hot. My board is quite faithful to the
original G0MRF article, using the 2x 42mm 3C85 toroid cores, which made it
unlikely that Dick's LOPT core was the source of the trouble. Although these
salvaged cores are not an exact equivalent, the ferrite material and the
other core parameters are certainly very similar, so one can expect very
similar performance.....
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