At 17:32 4-4-03 +0100, you wrote:
Dear Brian, LF Group,
At 04:46 01/04/2003 +0100, you wrote:
Only slightly off topic, but about
two years ago now someone described
completing the screening on a Decca 5501. I have lost the posting
but
I seem to remember that something "got hot". Does anyone
have the posting
still?
Brian CT1DRP
I think that was G4JNT's off-line TX using circuit techniques from the
Decca design. As I recall, When Andy initially put the TX in a steel
case, the casing around the tank coil got very hot due to eddy current
heating. The problem was overcome by placing aluminium sheeting between
the coil and the steel casing.
That is correct. Andy published his design in QEX.
73, Dick, PA0SE
The other effect
of putting additional shielding near the tank circuit coils might be to
de-tune the coils slightly - but I think with the layout of the Decca PA,
the effect of adding a cover on top as well as underneath would be
minute. A more significant issue is obstructing the cooling - the Decca
relies entirely on natural convection. On my unit I found that any top
cover must have plenty of vent holes in order not to substantially
increase the temperature rise of the heatsinks.
Cheers, Jim Moritz
73 de M0BMU
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