To:  towertalk@contesting.com 

Subject:  [TowerTalk] Problems on a 2el vertical Array 
From:  Tobias Wellnitz <T.Wellnitz@gmx.de> 
Date:  Fri, 09 Jan 2004 14:28:39 +0100 
Listpost:  <mailto:towertalk@contesting.com> 
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 groundlosses 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 (RG213  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 Zparameters with an MFJ259b: 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 (RG213): 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 XMAS. I was able to hear / "feel" about 34dB 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 1525dB 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 Toby, DH1TW _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 18003339041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk 
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