ORIGINAL MESSAGE:
On Wed, 14 Nov 2007 21:31:38 +0000, Felipe Ceglia - PY1NB
<felipe-listas@terenet.com.br> wrote:
>
>I've been looking at commercial available relay boxes, but beside being
>expensive, they use a lot of UHF connectors, which I would rather avoid.
>I am planning to use N connectors or, solder most of the cables directly
>into the PCBs.
>
>Do you suggest any particular relay model to use, that would comfortably
>handle legal power?
------------ REPLY FOLLOWS ------------
There are several approaches to this, any of which would work. Here's
my thinking:
My first concern is reliability. The last thing I want is a failure
during a contest at the top of a tower. Based on that, I would not use
connectors at all. Solder the coax directly to the relays.
As to relays, I would use 20 amp open frame relays with an insulation
rating of 15800 VAC or more. At HF, these work fine, just keep the
lead lengths short, no more than an inch or two. Mount the relays on a
piece of plastic, not on metal. This will help improve the insulation
between the armature and frame and also reduce stray capacitance.
Don't ground the coax braid to the enclosure. People think coax has to
be "grounded" to make it work, but it doesn't. Grounding the coax just
increases stray capacitance in this case. All the coax needs to see is
the connection to your antenna on one side and the connection to your
rig on the other. A ground at this point accomplishes nothing.
Enclose them in a weatherproof box. You can use an ordinary box and
seal it with some kind of removable sealant such as RTV silicone or
Coax Seal. Spend some time and make it absolutely water tight, except
for one tiny drain hole in the bottom. There will always be
condensation caused by temperature changes and it needs a way to
escape.
Outside of a direct lightning hit, it should last forever.
73, Bill W6WRT
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