[UK-CONTEST] Cables

Sun Jan 11 14:58:50 EST 2009

Hi Ken, all

I note your comments regarding losses incurred with open wire feeder
under certain circumstances. I do agree with your observation, and some
of my experiments have confirmed these losses and environmental issues
(see later).

In building my station, I originally planned to use the best coax I
could afford / lay my hands on, but due to the distances involved from
shack to aerial, coax is not an option. For example the distance from
the shack to the 14MHz tower is 110 metres plus 20 metres in height. 130
metres. The 14MHz tower is the closest, and the furthest tower is 250
metres plus 20 metres in height.There are others in between.(For those
who have visited Chez 'LCR you know the problems !)

As you can see the cable runs and losses involved are quite
considerable. The cost using RG213 is expensive (even buying in bulk on
1Km drums,and assuming the lorry carrying the drum can get up the
hill.... its expensive). Using LDF 4-50, well, I'll get a small
mortgage! 

I have carried out some experiments, using 450 Ohm Ladder line (the
black stuff you get from W&S etc) and home brew ladder line. Firstly the
450 Ohm Ladder line isn't 450 Ohm. Two batches I had, the first measured
out at 370 Ohms and and the second 400 Ohms. 

On a 100m run the purchased ladder line showed some loss, as you would
expect when compared to Coax. It was relatively easy to manage and
install. However, it suffered greatly (as you observed) when the weather
changed. Certainly keeping it above 10 feet off the ground helped, (as
opposed to heights of 3, and 6 feet I tried as well) but wind and rain
and snow etc etc caused some real changes in the chracteristics of the
line.

I then removed as much as possible of the plastic and kept it 10 feet
above ground. This helped stabilise it, but still some strange changes,
when the weather changed.

I then repeated the experiment with home brew open wire feeder, using
the classic calculation in the ARRL Handbook to provide the dimensions
of the feeder. Whilst a lot more time consuming to install, it was a lot
more stable than the purchased stuff. In the end I built a 100m run of
home brew open wire line, tensioning the two cables, between two points
made of two 10 foot gate posts, sunk 3 foot in the ground with a
strainer, (just like a strainer post used in fencing) and ran the open
wire line across the top of the posts and insulated with ceramic
insulators.

This worked well, with much more stability in the line. The recent ice
and snow up here did have an effect on the line, but a walk along the
line with a soft brush on a pole gets the snow off. 

Foretunately I do live in a remote area of North Wales, and background
electrical noise is very low, and interference is not really a problem.
So I am going the open wire feeder route, hence the references to the
Laport book. 

I wouldn't use Open wire feeder, of any type, on runs less than say 50
metres, (or of course as a matching stub, but that's a different story).

So Coax for some instalaations, Open wire for others.

Regards

Adrian MW1LCR

-----Original Message-----
From: uk-contest-bounces at contesting.com
[mailto:uk-contest-bounces at contesting.com] On Behalf Of Ken Eastty
Sent: 10 January 2009 21:11
To: uk-contest at contesting.com
Subject: Re: [UK-CONTEST] Cables

>
> Ken,
>
> I wish RFS cables were half the price of Andrews.  Sadly they are 
> competing in the same market and have more or less equivalent cables 
> so the new price is very similar.

>John G3UUT

John,

I bought (not for my own use!) several km's of RSF cable a few years ago
after a colleague pointed out that it was much cheaper then than the
equivalent Andrew product (there wasn't any discount for quantity),
perhaps they've changed their prices. When I've peered through the
fences (anorak
on) of Cellular installations most of the ones that I've seen seem to
use RFS as opposed to Andrew cable. Hopefully with the amount of drum
ends of hard line that seem to be around no one should have to buy short
lengths of these cables at new prices, I wouldn't expect to pay more
than the cost of RG213, however connectors might be another matter.

>I am going open wire feeder on all my HF aerials. Adrian MW1LCR

Adrian,

I don't recommend using open-wire feeder other than on very short runs.
Unless the line is really well balanced there's a problem with
interference pick up on receive and the characteristics of the line can
change dramatically with environmental conditions. In some cases
especially at the high end of the HF range when insulators are
contaminated the loss can equal that of co-ax like LDF 4-50. At least
with co-ax the loss is constant regardless of the environment and can be
overcome (on receive) with suitable pre-amplifiers. There are also
maintenance aspects to be considered when using open-wire feeders which
perhaps aren't so important in the amateur environment and of course
with a high power broadcast station the cost of co-ax for high power use
has got be a consideration. Many years ago when copper was perhaps
cheaper than it is today GPO HF radio stations built pre-1940 used co-ax
feeders made of copper tube at both transmitting & receiving stations.

>You forgot Westflex 103.

>Nigel G0VDZ

Maybe best forgotten, I don't like the few thin stands of copper braid
over copper foil, this in my experience doesn't make for easy
termination onto an N Type connector (no one doing a proper job would
use a 259's would they?)

73...

Ken

G3LVP

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