[UK-CONTEST] NFD Bracknell ARC G4BRA/P Low Power

[Dave Sergeant]

On 12 Jun 2005 at 18:06, Dave Lawley wrote:

> Nice writeup and pictures Dave
> 
> I was always told by G3RZP that you should avoid sharp bends in open
> wire feeder, as you can get reflections from the bend if you're
> unlucky. This is borne out by the text on page 12.31 of the fifth
> edition of the RSGB handbook, which judging from the prose style was
> written by G6XN.
> 
> Clearly this doesn't seem to cause problems in your case and I guess
> it is partly dependent on the precise length of feeder. I have always
> been careful to split sharp bends up into a couple of 45 degree bends
> where possible. Anyone else care to comment on whether or not it is
> important to avoid sharp bends in open wire line?
> 
> Dave G4BUO

Well spotted Dave. Well my suggestion that we put the pole a little 
further from the tent was ignored, with the result that we had a 
large excess of feeder and we had to devise some means of keeping it 
in the air. In fact if you look at our reports of previous years you 
will see that we always put the mast at the front of the tent, with 
the feed in at the rear, so getting round the problem. The power of 
the internet, it never lies... And at 2am I realised that we had 
forgotten to put the earth stake in - I couldn't convince John to go 
out and put it in at that time of the morning!!

As to whether the bends in the feedline matter, I suspect that Les's 
comments refer to open wire fed in a matched condition. In our case 
we were matching via a balun from the K2 internal tuner, which is in 
itself something you shouldn't really do! In this situation there is 
a high and fairly unpredictable standing wave on the feedline so I am 
not sure that any impedance discontinuity makes it any worse. But 
these sorts of nasties are largely not of great consequence at QRP 
levels, and the main thing is that it does work. We did however find 
we had to use the balun in its 4:1 position rather than the 1:1 
position we had used before as we got a poor match on some bands. The 
reconfiguration of the feeder probably had something to do with it. 
And it didn't seem to work as well on 20m as we would have expected, 
though that was probably just down to conditions.

73 Dave G3YMC

http://www.davesergeant.com