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[Ham-80211] "Commodity Class Phased Array Antennas" for HSMM?

David Young dyoung at pobox.com
Sun Aug 1 22:39:43 UTC 2004


On Sun, Aug 01, 2004 at 06:50:24AM -0500, Gerry Creager N5JXS wrote:
> While the design of the antenna element only has to be done once, its 
> implementation has to be done many times, as does the interconnect.  The 
> steering logic, which drives the elements in a manner to derive 
> horizontal and vertical tilt, and gain, has to be designed and built. 
> The phasing array or harness has to be fabricated.

I'm not sure what you mean by the interconnect.  I cannot speak about
RF interconnects.  However, for the control interconnecct, I think that
you could use a PC's audio output.  I'm not kidding.  Audio outputs move
voice coils all the time....

I am confident, as a "software guy," that the software problems are
tractable.  The hardware problems look pretty tough to me.  A software
feedback loop based on received signal strength could "train" the beam
onto the station that you want to talk to by moving the voice coil.

Regarding fabrication, my thinking is that you would download an "open
source" PCB design from the web and send it for manufacture.  (Although,
there are electrical engineers who make PCBs at home.)  You can buy a
6"x6" piece of alumina for less than $20 on-line.  I figure machining that
will be a pain, but it is nothing a determined HSMM hobbyist could not do.

BTW, the steering is horizontal only, although Kajiya tells how you could
do vertical tilt.  Horizontal steering is perfectly adequate for a lot of
applications.  For example, my main interest is in mitigating 2.4GHz
band interference while keeping a "mesh" neighborhood network connected.
You can steer the beam away from most interference with a horizontal rotation.

Kajiya proposed to build a 4-sector system with one of these antennas
in each sector, but that requires RF switches.  A 2-sector system might
just work, and no RF switches are necessary if you re-use the antenna
diversity switch.

Dave

-- 
David Young             OJC Technologies
dyoung at ojctech.com      Urbana, IL * (217) 278-3933




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