[Moon-net] Big Dish Optics/Drive Systems

[Pat Barthelow]

Folks:

I am walking through a planned operation of the Jamesburg 30 meter Dish in 
Monterey County for 1296 EME.  My first EME experience.
See:
http://maps.google.com/maps?f=d&hl=en&saddr=San+Jose+CA&daddr=Comsat+Rd+Carmel+Valley+CA&ie=UTF8&z=17&ll=36.403116,-121.646966&spn=0.003782,0.007231&t=h&om=0

http://groups.msn.com/towertrailers/shoebox.msnw?action=ShowPhoto&PhotoID=50

http://groups.msn.com/towertrailers/shoebox.msnw?action=ShowPhoto&PhotoID=65

http://groups.msn.com/towertrailers/shoebox.msnw?action=ShowPhoto&PhotoID=63

We have 500 watts at the PA output connector to feed a quad or yagi antenna, 
which will illuminate the dish via a 12 ft dia hyperbolic secondary 
reflector, from the cassegrain feed location at the center bottom of the 
dish.  The secondary reflector is about 60 ft above the bottom dish surface, 
and subtends about 12 degrees from that location.  My inexperienced logic 
says that I should illuminate that secondary reflector with a beam pattern 
that theoretically does not spill past the edges of the secodary reflector, 
or ideally a 12 degree  beam width.  So, I build a yagi or quad with 
sufficient elements/boom length to keep a tight beam width, say 12 degrees 
pattern at the -3db points.  Something like 16 db gain or so.   My question 
is, how much do I need to be efficient here with the feed, considering that 
the dish gain alone at 1296 is, say near 50 db?  What is the likely EIRP of 
the antenna system, assuming a feed power of 500 watts, say 13 db gain feed 
yagi, low efficiency illumination, and 50 db for the 30 meter dish?   Is 
this sufficient to do SSB EME contacts with other average 1296 EME stations?

Also, I am looking to communicate off line with any professionals with 
operations experience with Big dishes.  The contractor who in the past 
serviced this dish, was used to COMSAT/AT&T  cutting a Work Order, to have a 
couple of techs come from, say, Texas, and service the various systems that 
control dish movement.  This service call entailed paying transportation, 
and per diem for a couple of techs for a several days,  with specialized 
experience in the various dish drive systems, including the various motor 
drives, position encoders, gearboxes, limit switches, lubrication systems, 
control computers, etc.  In the Satcom industry, this cost is just absorbed 
as overhead, and cost of maintaining a large cash flow through the earth 
station, and could probably buy a complete big gun  EME station for ham 
1296, for only a few days of contract service.  Us local hams have to figure 
out how to operate safely, do the maintenace or safety checks, and have fun 
with the hobby.  We have also learned that ANY professional work on the dish 
is EXTREMELY expensive.  This was confirmed  when we explored what changes 
would have to be made, and what the costs would be, to change the dish 
function from Satcom to Radio Astronomy.   We are looking for institutions 
who may be interested and able to use the dish for Radio Astronomy, or 
perhaps Deep space communications.  Maybe we could be a  marketing tool for 
Cisco, HRO, M squared, or somebody, by painting an appropriate logo across 
the face of the dish (;>)
We just want to have fun, and not see this dish be reduced to scrap metal.

73, DX, de Pat AA6EG aa6eg at hotmail.com;
Skype:  Sparky599
http://www.youtube.com/watch?v=_lfWQybXHeM&NR
http://www.youtube.com/watch?v=bbCcGQXuqXw&NR