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Telamon · January 22nd 09, 05:33 AM posted to rec.radio.shortwave

In article
,
wrote:

On Jan 19, 10:05*pm, Telamon
wrote:
In article
,

wrote:
I plan to build a random wire antenna in my backyard with an RG8X
feedline.

I want to ground the feedline just before it enters the house.

Can I connect the coax to a SO-239 to SO-239 adapter (I think it's
called a PL-258), then attach the adapter directly to a ground rod
using a hose clamp?

Or, should I buy a lightning arrestor (e.g., Zap Trapper) and attach
that to ground rod just outside the house?

Thanks.

Zap Tapper is OK to use. There are others on this page you can use.
http://www.universal-radio.com/catalog/protect.html

--
Telamon
Ventura, California

Thanks for the links Telamon and RHF.

Here is my plan:

random wire -- 9:1 xfmr & ground -- RG8X -- lightning arrester &
ground -- RG8X (enters house) -- Rx

Actually, the random wire/xmfr part is the Par Electronics EF-SWL -
should be arriving in the mail next week.

Some questions:

1. Does the grounded lightning arrestor cause the coax shield to be
grounded? In other words, in addition to being part of a lightning
ground system, does the arrestor help reduce "common mode" noise?

Technically no but practically yes. Technically the arrestor is not a
common mode reduction device but practically common mode currents exist
on the coax from the radio then mains connection along with RFI it may
have picked up from the environment. The arrestor does ground the outer
coax braid but normally it does not affect the center conductor unless a
voltage rise causes the internal tube element to briefly conduct so in
effect it is a differential device.

I'm trying to follow the RF ground principles outlined by John Doty in
his article "Grounding is key to good reception". Here is the relevant
quote:

"The ground stake near the house provides a place for the common mode
noise current to go, far from the antenna where it cannot couple
significantly."

If the lightning arrestor doesn't ground the coax shield (I'm guessing
it does, since the coax shield touches the arrestor which is connected
to a ground rod), should I buy a 50ohm ground block and attach my
feedline to it just prior to the arrestor?

A ground block just grounds the coax shield. An arrestor also grounds
the shield but also has a device inside such as a 2 element tube that
conducts under high voltage conditions to the center conductor.

The technical notes on the ICE Radio Products website suggest that you
need a ground block and an arrestor, but maybe I'm confused.

For the arrestor to be effective it must be grounded so the high voltage
and current created by the lightening has a place to go besides your
radio.

2. I've read that, during a lightning storm, you should disconnect
the coax from the back of the receiver and disconnect the power cord.
However, I've also read that letting the disconnected feedline simply
dangle in your radio room during a storm is not a good idea. Any
ideas on how to safely disconnect the feedline from the receiver?

Disconnect it from the radio, put a cover on the end and put it outside
a widow.

Geoff, your post regarding "bonding" and following my jurisdiction's
electrical code is a good one. I will be looking into it asap.
Thanks.

Bonding means to directly as possible connect all grounds together. This
is done so all the appliances and things like radios are raised to a
common ground potential during a strike. This is just one way to protect
anything plugged into the mains supply and you during a nearby
lightening strike.

--
Telamon
Ventura, California

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