[TowerTalk] Lightning GROUND switch wanted RE:DE K0FF

[K0FF]

I have always built my own relay boxes using the Collins 5KW relays that are
(were) available from SSof Nebraska and double up the contacts. The best I
can hope for is reasonably low loss when in use, and of course it grounds
the antennas when deactivated. My thinking on this is that if everything
that CAN be grounded IS, it wont have a tendency to build up a static charge
and attract lightning. The exception is the fiberglass covering over the
typical 2/440 collinear antenna. It's a non conductor but I feel that it
picks up a static charge from the wind etc. and causes lightning to hit it.
These have been directly hit so often, there is something going on there if
my interpretation is correct or not. PS on more than one occasion I have
seen these antennas completely blown to smithereens with pieces found a
block away....and the equipment was totally undamaged...protected by a
Polyphaser.

But back to the relays for a moment..I was asked by a nearby HAM to help him
lash up his station, using the MFJ remote (wired) relays,and was shocked to
see that both his brand new units do not ground ANYTHING when deactivated,.
The contacts are there, and wired in the X manner, but the ground plane is
not attached to it in any way.  Is this normal? They can easily be modified
to to so by providing a heavy jumper from the contact pad to the ground pad,
but careful examination reveals no intentional means to accomplish this. Are
they all that way? Another thing I don't like on the X strap is that it's
thin brass and riveted. I use brass brazing rod crimped and soldered to 1/4
inch appliance right angle FASTON connectors which fit the spades on the
Collins* relays, and use silver plated copper straps insulated with Teflon
tubing for the wiring to the connectors. The lead length is longer than I
like, but seems to have no bad effect on HF that I can determine. Looking at
Tom's comment on spacing has me thinking that I'll add yet another relay to
the box, in series on the rig side, and arrange it to give the maximum
separation when deactivated. So far there are 2 relays on every antenna. The
first being at the tower to select the various antennas into the hardline.
The second is in a similar box on the grounding panel at the shack end, and
this selects the various tower boxes. Maybe that's enough separation but I
doubt it. Don't forget that the vast majority of the destructive energy from
a direct hit will be on the shield. This is best dealt with using a bulkhead
and single point grounding system.The rig-killing pulse on the
centerconductor comes from the lightning bolt "ringing" the resonant
antenna, so the power pulse is more or less a high RF field ON Frequency.


*made for use in, not by Collins. 2 form "C" contacts gold over silver,
fiber filled insulators, 12VDC.

Geo>K0FF
-----Original Message-----
From: Tom Rauch <w8ji@contesting.com>
To: labradley@mindspring.com <labradley@mindspring.com>;
TOWERTALK@contesting.com <TOWERTALK@contesting.com>; n4kg@juno.com
<n4kg@juno.com>
Date: Thursday, August 31, 2000 11:06 AM
Subject: Re: [TowerTalk] Lightning GROUND switch wanted


>
>> Do you really think that lightning would follow the relay
>> contacts to ground and not arc across to the other side?
>
>With the correct relay and the proper layout it could.
>
>I have dozens of feedlines and three telephone cables (one of them
>is 2500 feet long) entering my shack, and I use relays to
>disconnect critical equipment.
>
>The key is in the layout, and the design of the relay. You need
>relays with shorting bar contacts (similar to form X contacts) that
>tie the shorting bar to ground when de-energized. The relay has to
>be on a suitable groundplane, and leads have to be routed properly.
>
>A cheaper alternative is a microphone-type multipin connector, or a
>DIN connector for low current or Cinch-Jones type connectors for
>high current higher voltage, but if you want a relay it is workable
>with proper layout, relay selection, and grounding.
>
>The new RCS-10 Smart Control System has DIN connectors so it
>can be unplugged.
>73, Tom W8JI
>w8ji@contesting.com
>
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