[UK-CONTEST] 'Remote' radials...

[Mike Chamberlain]

Stewart,

Radials are all about reducing earth losses by providing a low loss path for
currents to flow back to the feed point of the antenna. So if your existing
radial field only occupies a limited arc of azimuth at the base of the
antenna the efficiency will be reduced relative to a full 360 degree span.
There will be some value in the existing radials but it depend on how big an
arc they present at the feed point.

My belief (and you may well get other opinions on this) is that the impact
on the shape of the polar diagram is secondary, radials operate in the
near-field, whereas, the polar diagram is primarily formed by ground
reflections in the far-field.

If it's possible, a better solution may be to use 3 or 4 elevated resonant
radials on a temporary basis - these seem to work exceptionally well.

One of the best references I've found on radials is ON4UNs Low-Band DXing,
chapter 9 in the fourth edition.  Well worth reading by anybody playing with
radials.

73,
Mike - G3WPH

-----Original Message-----
From: uk-contest-bounces at contesting.com
[mailto:uk-contest-bounces at contesting.com] On Behalf Of Stewart Rolfe
Sent: 16 June 2009 14:09
To: UK Contest Reflector
Subject: [UK-CONTEST] 'Remote' radials...


Hi all,

Continuing in the 'remote' vein I have a scenario for comment/advice:-

Shack in the garden centred on a decent system of radials trailing round the
garden and into a neighbouring farm field (sheep, not ploughed!)

Garden is wife's pride and joy so maybe I want to put up a temporary (single
band) vertical out in the field for a weekend's contesting. So how effective
can I expect the radial system to be when it's connected to the antenna
earth by a possibly longish earth strap? If the strap was electrically
isolated and 0.25 wavelenths the antenna earth should be very high impedance
and a lousy zero potential; by the same token a half wavelength should be
fine...?

Also what's going to happen to the radiation pattern in broad terms?

Thanks for any comments,

Stewart Rolfe, GW0ETF