> With each element being non-resonant and being fed with a
current source
> allows for a broadband system and reduces mutual coupling
between the
> elements.
Nothing can reduce the mutual coupling between elements. It
just is what it is for a given spacing and element.
Losses can swamp-out the mutual coupling so you don't notice
it. I do that with my RX arrays you see at:
http://www.w8ji.com/small_vertical_arrays.htm
Beverages are easy to phase because the losses swamp-out
mutual coupling effects.
The problem I see with these large active systems is:
1.) Ground losses are still the same. You still have the
same basic element efficiency problems.
2.) Mutual impedances cause all the elements to have
different impedances, and that means the power applied to
each element for maximum gain and maximum F/B varies wildly
from element to element with unidirectional arrays. If the
elements are close spaced and losses are low, you will even
have NEGATIVE resistance elements. This means multiple power
amps would produce an overall system having poor efficiency
both in hardware usage and energy conversion.
3.) Loading losses would remain just as high (or even be
higher) as when using a conventional array with elements
combined to a common feedpoint.
4.) Anything around the elements that bothers them, say a
power line that reradiates the TX signal and adds RX noise,
will still bother the elements the same amount.
> Naturally, what I just described is too limited to be
commercially
> interesting (except for the half dozen 160m/QRP/CW people
out there), but it
> would be fun to play with. It also might give me an edge
for 160m QRP.
> Since all the beamforming is being done in the DSP, you
are free to form
> more than one beam or null at the same time.
The spacing also determines how many nulls or main lobes
you'll have and where they are at. It is very unlikely
you'll be able to synthesize patterns with nulls and lobes
where you want, unless you carefully plan element locations.
When receiving, you could move nulls around at will within
limits of what the element locations allow, but you'd have
to live with main lobe locations. You could pick main lobe
directions, and take what you got (through luck) for null
locations. When transmitting, you could do the same EXCEPT
you would almost certainly give up gain and efficiency.
You could be forming a maximum
> gain lobe in the desired direction while interactively
nulling strong
> signals from other directions and doing active noise
elimination.
It doesn't work that way.
Every element is a source of signal and noise. Both are RF.
Both are on the same frequency. (If they are NOT on the same
frequency, then the receiver filter separates them for us.)
All you'd have is a fancy MFJ-1025, and all the same
limitations that apply to a MFJ-1025 would apply to the DSP
system.
You can't separate them and process them separately with a
phasing system. You can't null or subtract noise with
affecting desired signals from the same direction the same
way. You can't null strong signals from a given direction
without also nulling desired signals from the same
direction. You can't null a signal without creating a
response change in other directions, and you can't create a
response peak without creating a null.
You are stuck with whatever patterns you can create with the
element spacing and element locations you have.
73 Tom
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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