Phil Clements wrote:
>
> At 04:50 PM 9/12/97 +0100, you wrote:
> >What's the general feeling about toroidal dust iron cores in tank
> >circuits? I know some manufacturers seem to use them just fine at the
> >1500 watt level: I've always felt a bit dubious, but that may be just
> >innate conservatism. I've used them at 100 watts OK in a professional
> >transceiver, but what are the big ones like at 1500watts with up to
> >2:1VSWR?
> >
> Alpha has been using them for years, Peter. The 77 series uses stacked
> cores for 80 and 160 meters in the pi, as well as 20-160 meters in the L.
> 4500 watts is no problem, but it would take a third one in the stack for
> more QRO. The are advantageous as they are self shielding and can be place
> much closer to the chassis that an air-wound coil without degradation.
>
> (((73)))
> Phil, K5PC
>
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Hi Peter. I have had some experience with cores with the installation
of 160M in my Johnson Desk Kilowatt. They are easy to use and are not
really effected by there surroundings but!!. You must use the formulas
to calculate the heating effect of the freq and the Q etc. that they
will be used in. The Alpha tank was built using the parts and knowledge
available for the times, the cores are way too small for the culmlative
heat that will build when they are in the RF field. The polymers
holding the powder together will fail and the inductance will go way
down. My desk running at class C 800 w cc fully modulated 3.2k pep,
would need 4 of the 5 " cores stacked and insulated in a steady stream
of air to stay hot at best. Amindon will send you an engineering book
if you can come up with a company name.
Dont get me wrong I think they are wonderful items in low power
applications and rx circuits but one must over-engineere when using them
in tank circuits.
CUL 73
Randy
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