Topband: My Turn For a Brain Pick - Sanity Check

[James Wolf]

Jim,

Equipment wise, is this reciprocal if you use the array for your receive
measurements?

Jim, KR9U

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Jim Brown
Sent: Thursday, June 06, 2013 5:29 PM
To: 'TopBand'
Subject: Topband: My Turn For a Brain Pick - Sanity Check

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
All good topband ops know how to put up a beverage at night.
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Topband Reflector