From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
To: rsgb_lf_group@blacksheep.org
Date: Thu, 30 Mar 2000 14:10:13 +0100
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII; format=flowed
Content-Transfer-Encoding: 8bit
Subject: Re: LF: Amp metres
In-reply-to: <38E3350D.4717@xtra.co.nz>
Message-ID: <E12aepN-0006EL-00@mserv1b.u-net.net>
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>


> > Didn't Dud Charman's indoor antenna circus demonstrate the truth of the
> > axiom that a small antenna has the same radiation pattern as a very
> > small antenna?
> 
> I also believe that all short verticals have the same basic radiation
> pattern (the upper hemishere of a doughnut, with low angle suckin if
> ground loss is significant). 
> 

I was privileged to see Dud Charman's aerial circus in the 1960s as 
a schoolboy. For those who do not know, he had a large copper 
tray with a coax socket in the centre. He would then feed miniature 
antennas with UHF or microwaves and demonstrate their radiation 
pattern with a hand-held RF detector driving a lightbulb. Seeing a 
text book radiation pattern demonstrated in such a practical way 
was really amazing.

The flaw in this demonstration, however, is that it assumes little or 
no ground loss. I am sure that with practical levels of ground loss, 
the lowest angles are attenuated more on very short verticals than 
on taller ones.


Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm