Topband: double L antenna

[F3WT]

Le 29/09/2010 21:00, topband-request at contesting.com a écrit :


Jorge,
I used this antenna and even modelled it.( now i use a 2 turns wire 
Delta-loop because of even more reduced space)
Mine (K2KQ vertical before)  was much smaller . In fact you could call 
it equally well a double - zepp, bent at the ends, or simply a doublet 
BUT fed thru a Lecher transmission line ( in the middle) and a coupler. 
Mine was 18M vertical hanging along a neighbour taller condo -building. 
It was  2 meter above ground (poor),   bottom and top  bend with 2M 
horizontal length only . . My QTH is in town and this doublet had an 
open small angular  horizon  towards NW. Although a short vertical,by 
all means, ,it was symetrical, fed at midhight ( one half against the 
other). Worked well to NA for contests.Worked , of course much better on 
80 and 40 as is.
These questions about ground radials to have  or not to have refer back 
to elevated radials on  verticals as it does to base lines on 
Delta-loops. An extensive work (testing, modelling)  on performance of 
elevated radials ( vs. ground) has been performed or published by Rudy 
Severns ,N6LF in 2008  and Dick Weber , K5IU, with "Optimum Elevated 
radial Vertical Antennas"  in Communication Quaterly Spring 2007 as well 
as quite a few others ( Belrose, VE2CV f.i.)  ( www.antennasbyn6lf.cm 
or  google). Basically it discusses optimal length and says : of course, 
ground radials, the more the better, but ' elevated radials at resonance 
are 5 dB ( 1S point only) down w.r.t. same 4 radials laid on ground. 
(Table 1 page 2 of his experiment No.5) .Add relevant further 
downgrading w.r.t. usual advocated   number ground radials ( 30 or more, 
his experiment No1). His measurements showed almost a negligible 
reduction in short distance signal strenght ( exp. #1).
73,
Pierre,
F3WT

> Message: 2
> Date: Tue, 28 Sep 2010 12:07:36 -0400
> From: Brian Machesney<nekvtster at gmail.com>
> Subject: Re: Topband: double L antenna
> To: topband at contesting.com
> Message-ID:
> 	<AANLkTikP_V=UaSuL9Z2YQLrzgtTVnRUHy5u-hCMikQhg at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Jorge,
>
> I have used this "bent vertical dipole" on an 80-ft tower for two
> seasons. The vertical portion in my case is only about 70-ft, with the
> bottom wire about 5-ft above the (very poor) ground. Using this
> antenna for both transmit and receive, I have worked 132 towards DXCC
> and 31 towards WAZ from FN34.
>
> As the YCCC web site shows, you can make it into a two-band antenna by
> adding a second element in parallel with the first element (like a
> "fan" dipole). Since I only have two high supports (tower and one
> tree), I added a parallel element for 80m, spaced about 6-in from the
> 160m element. The two elements interact significantly, resulting in
> about 35-kHz 2:1 SWR bandwidth on 160m and about 150-kHz 2:1 SWR
> bandwidth on 80m. You can overcome this problem by terminating the 80m
> and 160m elements at different supports.
>
>