Hi Peter,
The Russians doorknob capacitors do well.
At least they look pretty robust. Do you happen to know the ratings? A
quick look on the web showed very high voltage ratings, but I couldn't
find any current ratings. Probably the current handling is high enough,
but it would be good to know for sure.
Mounting them with straps to the circuit board, as VK4AKV did, I would
expect the series inductance in those connections to degrade the
ultimate harmonic attenuation of the filters. Soldering the coils
directly to small straps bolted to the top sides of the caps should be
better.
Anyway, do you know where to buy them at ham prices? The few online
sources I could find sell them at prices that are quite similar to what
ATC procelain capacitors cost, which are far easier to mount, and far
better in terms of ESL. And those prices are simply too high, at $20 and
more per capacitor, plus shipping, plus taxes. At those prices, the set
of capacitors for the low pass filters would cost me about the full
budget I have for my entire project!
My fallback solution is homemade copper-clad mica capacitors, which are
inexpensive and effective, but not much smaller than those doorknobs,
and take some time making for the correct capacitances.
Manfred
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