A Message from Vic Michael, W3SDZ re an EME Project.
Subject: Phased Array Thoughts from W2IMU
Date: Mon, 31 May 1999 13:23:22 -0400
From: Hill-Top Farm : Vic Michael, W3SDZ
To: MOON-NET@VM.STLAWU.EDU
A few more thoughts for consideration about phased arrays.
Back in the sixties I attended a small meeting organized by now SK, Dick
Turrin, W2IMU at one of the NJ Universities. It was a small meeting, but
the subject was about how to build a "super amateur antenna" for moon
bounce. This was a time shortly after the Arecibo tests that stirred so
much interest in EME.
It was also made known there would not be many- if any- more opportunities
from such a large antenna, so Dick wanted to figure out a way to produce a
really large "Amateur" array that could be available on a regular basis to
keep interest alive. Dick had a great talent (I believe) for sorting out
the fundamentals of a problem. There were a lot of pipe dreams of some
amateur Ariecbo like -single aperture antenna. Here was his argument in
favor of a phased array system vs a single large aperture array:
A. Build the largest - but easily reproduced array for any band . A
single long yagi for six, four yagis for two Meters or - ten ft dishes for
432 up. The idea being, you build one module complete with receive
converter and transmit modules - then you build another copy- each on a
separate mount- until you have enough modules to begin getting results -
you keep doing this until you have a large array consisting of these
smaller realizable modules. He envisioned it as some huge club-type
project. People could specialize in making some individual part of each
module. In this manner, the array could be improved forever by simply
adding more modules.
B. We examined ways to simplify some of the difficulties of getting
such
a system working..
I should create a Web site with all the volumes of correspondence and many
hand sketched ideas that went back and forth between Dick and me about this
subject. Such a site might inspire some interesting projects.
VK3ATN was interested in doing EME after successfully accomplishing EME on
Two Meters with a large stacked rhombic array that would also work on six
meters. Some basic ideas we were examining at the time consisted of
putting a single long yagi for Six Meters on a very simple NON-motor
driven Polar Mount. As these modules were duplicated, each mount would be
placed along a North South Line. The idea being to make a Fan Beam that
would be narrow in declination, but wide in Hour Angle. You would set up
the mounts for a given Dec. and HA - then set up the phase shifts at an IF
frequency. You could have maybe up to an hour for the moon to drift
through the beam before the mounts would have to be changed.(Note:The same
IF could be used on several bands, thus one set of phase shifters could be
utilized on several bands.) We built some very simple ceramic selector
switch coax cable models of these phase shifters that consisted of being
able to switch in series different portions of a wavelength sections of
coax - (translate into phase shift in degrees). Dick measured these in the
lab with an HP Vector Voltmeter, and found you DO have to pay careful
attention to establishing a good RF Ground Plane around the switch area to
get accurate result. Each time you add a module, a phase shifter needs to
be part of the module.
You also need to work all the converters in all modules from a Master
Oscillator, but here again the phase shifts could be accomplished by phase
shifters placed between the Master LO Oscillator and each module.
With the assistance of the computer power available today vs then - all
this stuff is more doable than ever.
I don't want to take up a lot of bandwidth on this subject on the net, but
I would be glad to exchange correspondence more directly.
About two years ago, I survived a massive brain hemorrhage from an AVM that
burst one evening when I was working on my 1296 antenna. It came within
the slimiest margin of killing me - a quote from the brain surgeon that
saved my life - " I didn't give this guy a 2% chance of surviving the
surgery" ( If he was a Ham, I think he might have said something like
the chance for EME between two Dipole equipped stations with Gonset
Communicators) I did miraculously survive without any motor deficits and
am now very happily retired on the Hill-Top Farm where I build antennas.
After many false starts following the ice storm demise of my twenty seven
foot dish in the early seventies, I have a decent size Two Meter system
close to hopefully hearing some echoes again. Have four M^2 28 XP yagi
rigged for switch able H, V, RCP, LCP.on a BIG El-Az Mount, A Henry 3K amp
and some good receiver stuff.
Have visions of more antennas than I'll ever get time to build myself, so
am glad to share the ideas. W2IMU was a most wonderful friend to me and
many other people interested in EME. He inspired me to many wonderful
discoveries of the possibilities for large arrays.
73's
W3SDZ
Vic Michael
RR #1, Box 115
Muncy, PA 17756
vmichael@csrlink.net
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