On 2/7/23 17:58, Joseph Amato via AMSAT-BB wrote:
> I recently built two low noise amplifiers (2 m and 70 cm) for
> satellite work, hoping to mount them right at the antennas. They are
> in small Hammond die cast aluminum boxes. To mount the boards
> inside, I had to drill several 4-40 thru holes through each box. I’m
> worried about slow water seepage through these screw holes. Can you
> suggest a good way to seal them?
Hello Joseph,
Instead of drilling holes in the box for screws, I've used 1/2"
standoffs (threaded) and JB-Weld-ed them to the bottom of the box.
Rough up the general area where the standoffs will go in the box when
attached to the board and then screw the standoffs to your board. Use
that as an approximate template as to where they'll hit inside the box
and mark that with an indelible marker. Remove the board and put a
generous glob of JB-W in those four locations. Then put your board in,
submerging the standoffs in the JB-W. Let the whole assembly sit,
undisturbed, overnight. It will be nearly impossible to remove those
standoffs from the box, but you can easily unscrew the PCB for servicing.
Also, you have to assume that any sealed box is not perfect and that
you'll eventually get some moisture inside of it. So, I drill a small
weep hole (1/8") in the side which will face down and cover it with
window screen on the inside to keep out the spiders, etc. That will
allow the box to breathe.
I have an SGC ATU (CPVC/fiberglass box) and several other projects
outside which have had this treatment. They've all survived for more
than a decade with no observable corrosion or water inside the box.
Might I ask: Which LNAs did you build?
73,
--- Zach
N0ZGO
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