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.
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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