Ian White GM3SEK wrote:
> 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.
This makes sense, especially if you can adjust both phase and magnitude
of the elements).. In general, you can form N-1 nulls with N elements.
>
> 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.
>
I've been working on something similar, using LDG AT200PC antenna tuner
boxes as the adjustable LC networks. If one had multiple digital
radios AND software with the right hooks, one could do it digitally too.
I did some research a few years ago with 4 SDR1000s to do this for a
self calibrating radar phased array. The problem in the ham world is
that the user interface software for all of the likely radio candidates
(SDR14, SDR1000, Flex5K, SoftRock, etc.) does not lend itself to this
kind of work, and the work to create both the phasing stuff AND decent
ham modulator/demodulator/filtering/frequency controls is huge.
> 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
>
>
I'll give it a shot..
I'm always interested in UIs for such things too.
Jim, W6RMK
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