For high power HF and VHF amplifiers where I need to pass air through a hole, I
have been using copper hardware cloth, sold by McMaster Carr, instead of
aluminum screening.
It is made from heavy copper wire, and I use a resistance soldering (hot lips
we call them) device to solder all the way around the circle or square, to
prevent unraveling
of the mesh when it is handled. The solder is applied to crossing wires, a
little spot at every crossing. For VHF I am using same stuff with smaller
holes, but still allowing
good airflow, and also putting a long tube (5 inches) to act as additional
suppression. The screen wires need to be placed in direction of wall current
flow in a cavity circuit, if
used there. If at the top above the anode, beyond the short circuit (in a
quarter wave tuned circuit) then this doesn't matter. I soldered the entire
mesh into a copper ring,
using a hot plate, and had the entire assembly silver plated (it looked rather
crude after soldering). It now looks very professional and has low resistance
to RF current.
This is in the two air ports for the 3 megawatt 200 MHz cavity amplifier that I
am about to energize the first time either this week or next.
73
John
K5PRO
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