[TowerTalk] Problems on a 2el vertical Array

[Jim Lux]

Very nice work Tobias...

----- Original Message -----
From: "Tobias Wellnitz" <T.Wellnitz at gmx.de>
To: <towertalk at contesting.com>
Sent: Friday, January 09, 2004 5:28 AM
Subject: [TowerTalk] Problems on a 2el vertical Array


> Hi guys,
>
> over Christmas I set up a 2el vertical Array for 40m.
> I used 60 quaterwave long radials for each vertical.
> The spacing is 7m and I wanted to phase them with
> 123° (which seemed for me to be the best trade
> between ground-losses and f/b).
> I realised the array with the measured values.
>
> While testing the array on the air, I made several hundert QSOs on 40m
> (as DA0BCC) around X-MAS. I was able to hear / "feel" about 3-4dB
> additional dBs over one single vertical. But I'm unhappy with the f/b
ratio.
>
> The pattern shows, that I should have at least 10dB on EACH station and
> 15-25dB f/b on DX stations.
> I heard only a few DX stations where I really had 25dB f/b... but this was
> the big minority (maybe 5 out of 100).
> Often I didn't notice any f/b at all. (especially on stations closer
> than 2500km).

Close in contacts (or two bounce contacts) will have a high elevation angle,
so the relative phasing of the antennas is not as optimized as for a low
angle propagation.  Essentially, the antennas are closer together by
cos(elevation angle).

>
> Right now I have two possible answers / questions:
>
> 1. Is this the typical behavior of a 2el vertical Array ?

If your measured data matches theoretical expectations within 3 dB, on an HF
antenna over real ground, I'd be pretty happy.  Null depth (driving F/B) is
the first thing to suffer.

Consider also that the incoming wavefront is NOT a nice flat idealized
wavefront, but varies with time and probably has local wiggles.

Have you tried setting things up so you can swap front and back directions
to measure f/b directly?