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Re: Success with 4-foot dish



Hmm.. this is interesting-- if you are getting these results with a
6dB NF "IF-MOD + Stripline filter lengthening mod" Drake (like mine)
with 24 dBic gain, then this more or less proves that a 24 dB linear
(equiv to 21 dBic) TransSystem would give about those results,
which it does.. at least my OLD DEM preamp (0.68 dBNF/11.78 dB gain) with 
the Drake (about 1.25 dB system NF/35 db system gain) and a
Conifer 24 dBi (linear) gave about S-5 beacon and S-1 to S-3 QSOs. (on a 
Kenwood R-2000 with the VHF converter)

The TransSystem 3033 is (stock-- no mods) about 1.4 dB NF/28 dB gain 
system-- so they should be very close.  [All measurements were 2401 MHz in 
123 MHz out]

I'll do my best to find the back of the brochure that I wrote all the
numbers on from the Dayton Weak Signal banquet NF measuring tonight, so I 
get the info 100% right --I had an important family issue come up last night 
so I renigged on the promise of doing that last night.  I suspect the 
naysayers will question the measurements, anyway, even though they were done 
by Al Ward W5LUA himself...

I think this is showing that with proper attention to details, it is
possibly to have an adequate to good mode-S system for around $115
(the price K5GNA sold the whole kit for at Dayton w/xtals, etc.)
that fits into a 3'x3'x3' area-- so comparing it with a 14 element
KLM 2m and a good preamp, mode-S is both cheaper and smaller.  The
AMSAT crew definately had a success here.

I think the key is to not mess around with helixes too much-- do small 
dishes.  Back when I used to do WEFAX, I tried a loop yagi first-- but when 
In discovered a 2 foot MA/COM dish outperfomed the loop yagi, I've never 
looked back since.  (OK, I tried a 33 turn 2401 helix-- but even a 18" dish 
seems to work better)

Fred W0FMS


>From: "Edward R. Cole" <al7eb@ptialaska.net>
>To: <amsat-bb@AMSAT.Org>
>Subject: [amsat-bb] Success with 4-foot dish
>Date: Tue, 22 May 2001 07:00:56 -0800
>
>Hi all,
>
>At 1410 [0610 local] I had success in hearing AO-40.  Of course the squint
>was ~4 degrees and elevation about 30 degrees [and the air temp about 20F].
>  So I crank the dish up manually and pull it around to the correct 
>azimuth,
>and holding the 5-turn helix with Drake attached in front of the dish [no
>feed mount yet] I find the beacon immediately.  Its peaking 3 S-units over
>the noise.  Then I tune up the band and hear 3 or 4 stations on varying
>between 1 and 2 S-units over the noise [no LEILA candidates], but if I were
>not freezing my butt and my hand aching from holding the feed, I would be
>copying pretty good. {some of you need to learn how to talk faster on the
>bird...he! he!}
>
>I guess the Drake is not broke, nor the feed.  BTW the 5-turn helix has too
>narrow a beamwidth for this center-fed dish so I'm only effectively using
>about 50% of it.  That means the gain ~24 dBic.  So I come back inside to
>thaw and have a coffee and check Gene's spreadsheet.  It predicts 15 dB S/N
>for the numbers [about S-3 on the beacon]; just what I'm hearing.
>
>Well tonight I'll work on a feed support and coax runs to the dish and 432
>antenna.  AOS is 0643 [2243 local] tonight with a small squint.  Hoping to
>be QRV on mode-US.
>
>Ed, AL7EB
>BP40iq
>PS: with a preamp this ought to be "smoker"!
>
>----
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

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