|Subject:||[TowerTalk] Problems on a 2el vertical Array|
|From:||Tobias Wellnitz <T.Wellnitz@gmx.de>|
|Date:||Fri, 09 Jan 2004 14:28:39 +0100|
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 calculated the following impedances, using EZNEC with Mininec ground. (incl 3 Ohms ground losses):
Ant1: 30,7 +j31,4 Ohm Ant2: 19,2 -j16,9 Ohm
Applying the Christman method, I obtain the following cable length (RG-213 - vel. factor 0,66)
to Ant1: 8,43m to Ant2: 13,79m
At the common point of the cables I calculated the following Impedance: Z = 34,4 +j3,7
----so far the theory-----
In order to build up the array as precise as possible, I messured the Z-parameters with an MFJ-259b:
Z11 = 37 +j3,7 Z21 = 25,0 +j13 Z12 = 25,0 +j13 Z22 = 37 +j7
Out of this I calculated the drive impedances (I skip the details):
Ant 1: 22,3 -j9,9 (1A / 0°) Ant 2: 27,5 +27,3 (1 / 123°)
out of this values I calcuated following cable length (RG-213):
to Ant1: 10,4m to Ant2: 14,92m
At the common point of the cables I calculated the following impedance: Z = 38,8 +j7,36
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).
Right now I have two possible answers / questions:
1. Is this the typical behavior of a 2el vertical Array ?
2. Did anyone set up such an array, using the messured values ?
2.5 How MUCH can I trust that MFJ 259b ????
Best greetings, 73
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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