[TowerTalk] My Turn for a Brain Pick / Sanity Test

Wes Attaway (N5WA) wesattaway at bellsouth.net
Thu Jun 6 17:51:20 EDT 2013

Take the reflector/director down (remove it) and see what happens.

----------------- Wes Attaway (N5WA) ------------------- 
1138 Waters Edge Circle, Shreveport, LA 71106 
    318-797-4972 (Office) - 318-393-3289 (Cell) 
        Computer Consulting and Forensics 
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-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim
Sent: Thursday, June 06, 2013 4:36 PM
To: towertalk at contesting.com
Subject: [TowerTalk] My Turn for a Brain Pick / Sanity Test

I'm building a simple 2-el vertical array for 40M, with one element 
driven against radials, and a passive reflector with an equal number of 
radials.  NEC predicts 2.7 dBi over lousy ground at 15 degrees, with 
peak gain of 3.6 dBi at 25 degrees elevation, and F/B of about 8 dB.

We've got this set up in W6GJB's pasture, roughly 5 miles S of me, with 
me centered on the main lobe, and I'm looking signal strength with my K3 
reading relative dB (and with AGC turned off).  Our signal is 35 dB 
above the noise level with Glen's KX3 at 3 watts. Terrain is hilly 
between us, and we have 16 radials on both elements.

We're making three measurements -- with the array as designed, with the 
reflector shortened by 3 ft (which should make it director) but still 
connected to the radials, and with the reflector simply insulated from 
the radial plate.

What I hope to see if the antenna has the predicted directivity is 3 dB 
difference between the designed array and the reflector floating, and 
6-8 dB difference between the array as designed and reversed.

What I see instead is the same signal strength for all three 
configurations within 0.2 dB.  So the question is, why?  A vertical plot 
in NEC shows the F/B at all elevation angles, all the way down to 1 
degree and up to 80 degrees.

73, Jim K9YC

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