Tom wrote....
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
Tom,
Actually, there is a difference between this and a single MFJ-1025. Each
element's signal is being phased and amplitude adjusted in the DSP as a
complex signal before you do the combining. This is a key point that all
the computing is done with both the I and Q part of the signal from each
element. It gives you more options when you are beamforming nulls.
Jim,
I think you see what I was getting at with the current source tx amps and
the rx buffer both at the feedpoint of each element. That way the phasing
is completely determined by the DSP and the feedline lengths for both tx and
rx.
I am probably way off on thinking that I can reduce mutual coupling very
much with non-resonant elements. It does make the system simpler, though.
As long as the amps can handle the reactive loads.
As for efficiency, there is still the problem of copper and ground
losses. In my economy, I would still consider those to be losses after the
output and not before. In other words, I would consider it a QRP system if
I had 5 watts going into Rrad and Rloss, instead of running more power so
that I have 5 watts into Rrad alone. I think the latter is what you were
suggesting in your original post. That's the way I would run it, but I can
see the other argument, too. But other than that, I don't care if it takes
me 25 watts of power supply power to accomplish getting a clean 5 watts
distributed into the reactive elements.
Anyway, its easy to see that this is the dream of a ham turned software
guy, isn't it? There are about 10 analog components and the rest is
software.
Dudley - WA1X
-----Original Message-----
From: Tom Rauch [mailto:w8ji@contesting.com]
Sent: Sunday, March 06, 2005 6:37 PM
To: Dudley Chapman; towertalk@contesting.com
Cc: richard@karlquist.com; jimlux@earthlink.com
Subject: Re: [TowerTalk] Active phased arrays.
<snip>
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
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