Using coax shield for long wire antenna

Bob

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Aug 24, 2002, 8:47:51 AM8/24/02

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Anyone have any experience good/bad with using the braided shield of
coax as a long wire antenna? I have a large roll of RG-59/U with
copper braid and a LARGE lot to run it over. I want to be able to
monitor (no transmitting) on 160 meters and below. I thought of using
the shield as the antenna and a local ground at the radio. (Lightning
protection will of course be provided as well.

Is there any advantage to doing this due to the potentially larger
diameter of the antenna rather than using simple wire? I know there
will be more ice loading on it but another thought is laying on the
ground and using it as a LW antenna.

Any thoughts or input welcomed.

Thanks Bob

'Doc

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Aug 24, 2002, 3:00:47 PM8/24/02

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Bob,
There really isn't any advantage to using braid as an
antenna, and there are a few disadvantages. The primay
disadvantage is that weather tends to 'eat' copper braid
fairly quickly.
The diameter of the conductor makes very little differnece
at HF, especially on 160 meters. Any conductor that is
large enough to hold up it's own weight will work as well as
any other conductor in almost all cases.
Using RG-59/u for the conductor will work. It may not be
the 'best' use you could put it to, but it should certainly
work.
'Doc

Owen Duffy

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Aug 24, 2002, 7:29:22 PM8/24/02

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Bob wrote:
>
> Anyone have any experience good/bad with using the braided shield of
> coax as a long wire antenna? I have a large roll of RG-59/U with
> copper braid and a LARGE lot to run it over. I want to be able to

From Belden's data on 9204 (RG/59) max tension on cable is 344N, and its
diameter is ~6mm.

If you planned to install it with 5% sag, WLL 25% of UTS, and to resist
winds to 40m/s, the maximum span would be less than 4m.

You might achive higher UTS by effectively tying the innder conductor to
the braid... but essentially standard RG59 has high wind resistance and
low tensile strength.

> Is there any advantage to doing this due to the potentially larger
> diameter of the antenna rather than using simple wire? I know there
> will be more ice loading on it but another thought is laying on the
> ground and using it as a LW antenna.

Ice loading will exacerbate the problem - additional gravitational force
and additional wind loading.

Owen

Bob

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Aug 25, 2002, 9:21:57 AM8/25/02

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Yes, I tend to agree with the fact that it would not make a good
elevated antenna. Since I have a large roll of it and its not really
good for use as coax feedline for me, does anyone have any good links
for "on-the-ground" antennas for longwave reception? It would be
fairly stealthy and I could just unroll it across an unused piece of
the property.

Thanks for the help!

Bob

Richard Clark

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Aug 25, 2002, 2:26:32 PM8/25/02

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On 25 Aug 2002 06:21:57 -0700, emergency...@yahoo.com (Bob)
wrote:

Hi Bob,

From the way you ask the question it seems you already anticipate the
snake-in-the-grass antenna. I was about to respond to your other
query with a suggestion of a Beverage design.

Elevate 2,3, or more wavelengths of your cable a dozen feet and listen
on the shield. If you cannot elevate it, then lay it out and listen
on the center conductor. The specifics as to if the far end is
terminated, opened, or shorted escapes me... that should resolve with
simple testing. You should have a good local ground screen (8 radials
out a couple dozen feet - use cable shield here too, along the ground;
no need to strip it, insulated will work fine - probably better).

73's
Richard Clark, KB7QHC

'Doc

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Aug 25, 2002, 2:41:17 PM8/25/02

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Richard,
Terminate it in a resistor of the same value as the
coax's characteristic impedance (75 ohms). Will it be
a great antenna? Nope, but it will work. Needs to be
at least 1 wave length long, and is a 'single band' thing.
'Doc

Thierry

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Sep 4, 2002, 10:03:11 PM9/4/02

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'Doc <w5...@icok.net> wrote in message news:<3D6924C0...@icok.net>...

Hi,

Full agree.
As SWL I'm using a mixed simple electricwire soldered to a coax RG58.
The longwire is 40m long and is tied at about 3m high .
My location is on top of "hills", 250m /sea, openfield. In 48hrs I
listened over 87 DXCC and twice as more after 3 months.

But on another location, I use a sloper of 15m connected to an indoor
cable 10m long (so for a total of about 25m of mixed simple electric
wire+coax) but here the signal quality if poor and I have QRM to
generators nearby.
But in both QTH i get a SWR of 1:1 or near or sometimes 1.5 on the 17m
band.

So depending your location the long wire mades of simple lectric wire
or even a coax give excellent results.

I have think to terminate the wire with a terminator but I din't
install it.

See my QTH installation at
http://www.astrosurf.com/lombry/qsl-longwire.htm

NB. To resolve my QRM problem on all HF bands I'm currently replacing
my sloper with a magnetic loop ALA-330.

A+
Thierry
ONL5183