[TowerTalk] Front-to-back / Front-to-rear

[Ian White GM3SEK]

Jim Lux wrote:
>The other thing, not well accommodated by the classic sidelobe sorts of 
>metrics, because the typical HF antenna has a very broad main lobe, is 
>the thing of performance when deliberately pointed off the desired 
>signal to further suppress an inteferer that is not separated by a huge 
>angular amount.

There's an interesting demo program from the British consultancy firm 
Plextek, which shows how a 'four-square' configuration can be adjusted 
to produce two simultaneous nulls while still maximizing the wanted 
station.

The trick, of course, is to optimize the current magnitudes and phasing 
to do this. The program is intended to show off Plextek's proprietary 
algorithm - as you move the azimuth bearings of the wanted and unwanted 
stations, it recomputes on the fly. The program can also be used in 
manual mode, and for example you can set up the classic quadrature 
phasing or any of the 'improved' schemes.

The program only works in 2D (free space or ideal groundplane) so you 
don't see the effects on the elevation pattern. Still, it shows what 
could be done if we had total control over the element currents and 
phasing.

http://download.plextek.co.uk/AKS06.zip


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73 from Ian GM3SEK