[UK-CONTEST] Cables

Sun Jan 11 16:49:17 EST 2009

Adrian,

If it is any consolation, the now defunct HF station at Rugby used 
open wire feeder and at that location  many of the antennas were huge 
distances from the transmitter buildings.  The characteristic impedance 
they used was quite low as I recall, circa 240 ohms.

73 Bob G3ORY

>----Original Message----
>From: rees.a at btconnect.com
>Date: 11/01/2009 19:58 
>To: "Ken Eastty"<ken.g3lvp at btinternet.com>, <uk-contest at contesting.
com>
>Subj: Re: [UK-CONTEST] Cables
>
>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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