Topband: My Turn For a Brain Pick - Sanity Check

[Greg - ZL3IX]

Hi Jim,

Have you tried measuring the current in the parasitic when connected?

73, Greg, ZL3IX

On 2013-06-07 09:29 a.m., Jim Brown wrote:
> 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.
> _________________
> Topband Reflector
>
>