[UK-CONTEST] Long Distance Feedlines

[Don Beattie]

No experience of this, Adrian, but I guess that the basic twin line will be 
very low loss (provided it is properly supported) . The baluns will 
introduce a bit of loss at each end, but nowhere near the 8dB.

The only experience I DO have of open line is in field day, where I found 
that the voltages in the immediate vicinity of the line were not truly 
"balanced" resulting in some RF feedback problems (and this was with only 
100 watts) So I would suggest taking the RF out of the shack on co-ax, then 
having the first balun at least 10 ft from the equipment (perhaps a little 
more) and then continuing as you propose.

Perhaps others will have more relevant comments.

Incidentally, for future reference, there is a good alternative to LDF now 
which is Eco-Flex (AirCom) which for HF has an attenuation about the same as 
LDF4-50. It's also flexible and a quarter of the price !

73

Don, G3BJ


----- Original Message ----- 
From: "Adrian Rees" <rees.a at btconnect.com>
To: <uk-contest at contesting.com>
Sent: Monday, September 25, 2006 10:44 AM
Subject: [UK-CONTEST] Long Distance Feedlines


> Slightly O/T but this is the Forum that an accurate answer will come 
> from....
>
> I am planning on having a go in CQWW SSB, but will have to enter "Field 
> Day" Style, as I have nothing in the air at the moment....so:
>
> I will use an A3S for 10-15-20 and a Battle Creek Special for 160-80-40. 
> Feeding the lower band aerial is not a problem, as it will be about 60-70 
> Feet From the shack, (which in reality will be an old cow shed. Told you 
> it was Field Day Style !).
>
> However, the A3S will be on a short mast, about 10 metres in the air, and 
> about 300 metres from the shack.
> (I could move the A3S closer to the shack, but would loose the benefit of 
> its location..... Its located effectively on a 300m Cliff, giving 
> significant benefit to the US / Pacific and Europe. Moving it would reduce 
> this benefit.)
>
> But ... feeding the A3S with RG213 would cause something like 7 - 8 dB of 
> Loss. Feeding with Heliax would be better, but, the Heliax I have is in 
> 55-60m Runs, and I don't really want to use this for a temporary 
> installation.
>
> What I do have is some 300 m of 450 Ohm Open wire feeder. So, I was 
> thinking, how about a pair of 9:1 Baluns at each end, thereby using the 
> 450 Ohm Feeder as "transmission line" across the field to the A3S.
>
> The question is, has any one done this, and if so what losses do you 
> incur. (I am trying to figure out is it really worth doing this, or should 
> I just think about moving the shack and or the A3S ?)
>
> Thanks
>
> Adrian MW1LCR
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