Topband: RX antenna pattern

[Tom W8JI]

Near field patterns have almost nothing to do with far field patterns, so 
that would be a great deal of walking and require a pretty sensitive 
instrument. To be in the area where the pattern is reasonably formed, a 
person would have to be at least a wavelength and at least 5-10 times the 
physical area of the antenna away from the antenna, whichever is greatest.

For example, my transmitting four square on 160 has not reasonably formed a 
consistent pattern until I am out about 2500 feet.  A small loop stabilizes 
at about a wavelength.

I'd expect the BOG  to approach the distance of the four square.

There are two reasons for this. One is the induction fields have not been 
fully dominated by the radiation field until near a wavelength for a very 
small antenna. The other reason is to form the pattern, the sense antenna 
and measured antenna have to be so far apart that all radiating areas of 
each antenna appear to originate from a single point in space.

If it doesn't look almost like a single point for both the sense and main 
antennas, the pattern won't be the actual pattern.

The way you get around this is to add a dielectric sheath in the model, like 
wire insulation, that slows the wave like ground would. Then, if you match 
the current levels and phase, you will pretty much get the correct pattern.

When I was working with slow wave antennas, I measured phase shift and 
currents and adjusted the model to match the antenna. If you do that, it 
doesn't matter if the wire is above earth in the model. It comes out a close 
match.

Otherwise, be prepared to drive a few miles while confirming pattern.  :)






----- Original Message ----- 
From: "K1FZ-Bruce" <k1fz at myfairpoint.net>
To: "Topband" <topband at contesting.com>
Sent: Wednesday, June 17, 2015 10:15 AM
Subject: Topband: RX antenna pattern


>
>
> BOG antennas are difficult to model. Programs do not like wires on/under 
> ground.. It is possible to find actual BOG, and Beverage patterns at 
> ground level.
>
> Feed a few watts of RF signal into the BOG/Beverage antenna. Use a 
> portable SW receiver with S meter to walk around the antenna to take 
> measurements and plot.
>
>
> Hope you have friendly neighbors !
>
> 73
> Bruce-K1FZ
>
> www.qsl.net/k1fz/bogantennanotes/index.html
>
> www.qsl.net/k1fz/beverage_antenna.html
>
> _________________
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