[UK-Contest] Inverted V help (Ian White, G3SEK)

[Ian White, G3SEK]

Andy Summers wrote:
>I'd disagree that bent & folded wires necessarily increases the risk of 
>feeder radiation. RF on the braid can only occur either by the outer RF 
>'skin' being excited by the antenna directly, or due to the transition 
>from an unbalanced feedline to a balanced antenna. As far as the latter 
>is concerned, bending the wires can only make the antenna less 
>balanced, can't it?

In this particular case the dipole is being bent and folded differently 
on its two legs, in order to make it fit in a small garden.

This means that the currents on the two legs of the dipole will not be 
exactly the same at the feedpoint, and the difference due to that 
unbalance will flow down the outside of the coax shield - unless a choke 
balun is there to stop it. There still remains the problem of induction 
further down the shield, but at least you've stopped the currents from 
being launched onto the shield from the direct connection at the top.

Sorry to be a "purist" about this... but my experience has always been 
that RFI will crop up at the slightest excuse, so I try to play safe. 
Getting back on-topic, fire-fighting RFI problems during a contest is a 
waste of time and points, if those problems could have been prevented 
instead.

-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                            Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek