On Wed, Oct 06, 2010 at 09:39:58AM -0600, John Lyles wrote:
> 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.
ISTR someone selling, or at least advertising, silver plated copper mesh
on one of the ham-related mailing lists, or possibly in one of the
newsgroups, before my IDE controller died wiping out two hard drives.
The big amp sounds like a real beast, based on the above and what you've
written earlier about it. Images will be welcome (I'll host them), and
I'll be very interested in what you have to say about the first-light
event after the fact.
--
Mike Andrews, W5EGO
mikea@mikea.ath.cx
Tired old sysadmin
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