Not
really microwaves and certainly not LF, but hopefully someone can
help...
I've been reminded that I promised to finish a 200 Watt
70MHz solid state PA, a project started some time ago and got put on
hold. I'm stuck for a suitable ferrite core for the output
transformer. It needs to match approx 3 ohms load resistance to 50
ohm output. The windings will be made using either conventional wire as in
HF PAs, or made from semirigid coax with shunt outer, series inner. The
latter will need a physiacally larger core to accomodate the wire
thickness.
Some cores I did have that 'ought' to have worked taken
from a 35 watt broadband PA (0.5 to 1000MHz) failed miserably and
got seriously hot no matter what winding configuration was used. In
that original PA they were acting only as common mode chokes and presumably
didn't have to carry nearly so much flux.
Does anyone have details of a suitable core/material,
or better still have a core going spare
:-)
The PA uses an MRF 141G Mosfet device rated for 300
Watts out with 14dB gain. The circuit itself is quite
simple - see the data sheet for teh MRF141G - and would have been finished
a long time ago but for the output transformer.
Andy
G4JNT
