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RE: DSS Dish



>From: "Acito, William" <William.Acito@brooks.com>
>Ed,
>
>Can I assume that the DSS dish didn't cut it? You've gone the Primestar
>route?
>
>Bill
>w1pa

Well, sort of.  

The note you reference is from last Friday.  I have since recounted my
experience Friday night with the DSS dish, but in brief...didn't hear
"nuthin" with it.  Mike had a small BBQ dish [about 9 x 30 inch, I guess]
which Mike thinks is about 21 dBi gain [derates to 18 dBi for
cross-polarization to a dipole feed].  With it I could just barely make out
the beacon at a squint of ~7 deg, range 61,000 km.

I have gone back to study the article by Paul Wade on the DSS dish and
conclude that I did not have the helix feed in the proper focal distance
and/or position.  I plan to play with it some more, but even with a good
preamp, the dish is about -3 dB from what is looking to be a minimum
requirement.  When I began planning on this dish before launch, I knew it
was below the recommendation, but it looks like performance is a bit down
from what the Amsat articles were saying.  Also, I think the articles
didnot take into account the -10 dB transponder penalty.  P3G to P3D
arrived at a 17 dB S/N with 18-19 dBic antenna gain.  I'm getiing at most 3
dB.

So, yes I'm moving up to a bigger dish.  The question is whether it will be
the 4-foot solid aluminum Andrew Comm dish [not a Primestar] I used last
night or maybe the 33 inch offset feed dish I currently use on my Echostar
"Dish Network" TV system.  It would be about the max. size dish that I
could use with a G-5400 rotor.  The Andrew will take a pipe in the ground
with a custom az-el drive.  It weights about 40 lbs.  I'm using it right
now as it was easy to mount for manual pointing and has 28 dBic gain so the
barefoot Drake has plenty to work with.  BTW I am using the same 5-turn
helix that I built for the DSS dish, so it does not illuminate the 4-foot
center-fed dish well.  My guess is maybe 24-30 inches of diameter, only.
If I build  3-turn helix I should see at least 4 dB more signal with this
dish.

But after I get my preamp, the 33 inch offset dish should perform really
well [maybe 8 dB better than last night with the 4-footer].  That should
just about find the transponder noise floor [maybe].

Anyway this is fun experimenting, and hopefully my goof-ups will help
others in their quest for S2!

Ed

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