jawod wrote:
Dave wrote:
well, 'adaptive beamforming' is two words...

'beamforming' means forming a directional 'beam' using an antenna. be
it a simple parasitic array like yagi's or a complex array of driven
elements like a flat panel radar. most often when you talk about
beamforming it is more like the radar arrays or other large array that
combines signals from many small antennas to form a very directional
beam.

'adaptive' means forming the beam in a way that makes it work better
in the environment, or adapt to it's surroundings. this is often used
to form beams to maximize a received signal while notching out
interference. so you use an algorithm to measure s/n ratio or some
other parameter and adjust power and phasing of the individual
elements to get the best signal you can. its harder to adapt a
transmitting antenna since you need some kind of feedback from the far
end to let you know if the beam is getting better or worse as you
adjust it.


"john" wrote in message
...

I came across a reference about adaptive beamforming in the ARRL
Handbook. The reference was from QEX which I don't yet subscribe to.

Anyone care to explain/discuss this neat concept?

John
AB8WH



Dave,

Thanks for responding.

Given the need for "stealth" antennas, Is there /are there design(s)
that create small footprint antennas that function as larger traditional
ones?

Can a longwire be divided into small segments that are independently
controlled such that the sum of the parts behave differently than the
whole?...and can this effect be altered via software?

Has anyone been working on this approach?

John
AB8WH

You can do it with dipoles, like the HAARP transmitter. It has the most
gain per acre than any other antenna. You can really use any antennas,
just the phasing becomes complicated. You need to ensure all antennas
are identical and have the same impedance and reactance etc etc.

Its a bloody complicated exercise to design such an array. Look up
the varios web pages on google.

The DF arrays used around the world are receive only versions of these
antennas. Look up "super resolution DF arrays. They amazing stuff!

A number of ANtenna companies sell wide band vertical arrays for
transmitting. They consist of 12 vertical in a circle with a radiator in
the centre. They then have a smaller inner circle for the higher
frequencies.

I would like to pick up one of the Super DF arrays one day on the
surplus market, oh boy what fun you can have! They can work out the
location of a station with one DF receiver. Called single station
Location.

Beam forming on receive and transmit are the same thing in reality.
However its not as easy building phase stable antennas on transmit that
cover 1.8 to 30 mhz.

If you work it all out and can do it for 500 dollars let me know. I
would like to buy a beam forming antenna for shortwave receive. With
cost of DSP chips dropping who knows maybe some day some smart ham will
come up with a Super resolution cheap df system/ beam forming transmit
system.

Ocean radar also use these complicated systems.

HF antennas for all locations RSGB has a article in their for beam
forming using compact 1 metre loop antennas, you might want to check it
out. Its a homebrew version of the Hermes Loop system. Same thing
could be done on transmit with magnetic loops. If you took a ham 8
circle vertical array and substituted magnetic loops you could perhaps
do it. You need someone smart like W8JI to figure out all the
mathematics and details.

Pat