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Re: P3D information


At the time, I was unemployed just out of college, and I used
a (I think) 10 turn helix on 70 cm homemade literally out of
trash the neighbor threw out (tubing) and 2x2's on a roof tripod that
I had fashioned a wooden base for and armstronged it for az/el.
(it was cheap, the best I could do)

I could work about 25% of the apogees, and never got good reports
on SSB (when most others were armchair copy.. it was embarrasing enough I 
didn't operate much).  CW was ok at 10W though.  I certainly do see how with 
KLM's and 20W you could be solid. (I wheeled the whole
thing out of the garage to use it.. it was kinda cool now that I think of it 
:-)!! )

But I think we need to remember that it isn't always easy to be able to find 
the real estate to put up an AO-10/13 class antenna system.
I have a house here in Cedar Rapids that I could (and did) put antennas up, 
but it would take me about four pages to tell the complete story on how hard 
it was to find a piece of property that didn't have covenants stating: "No 
antennas and/or radio transmitting of any kind".  Even out in the farmland 
here in Iowa, most of the properties/developments have that restriction 
(unless you buy 35 acres of land).

Also the arguement that Mode-S downlink is really expensive is questionable. 
  Take a look at all the "Drake" converters.. other
MMDS converters are probably as suitable.  The old DEMI unit I have
didn't cost much more than $100, and I'm sure Steve Kostro at DEMI will have 
a reasonable priced unit as soon as P3D actually launches.  SSB Electronics 
stuff, even though very professional quality is quite expensive, to the 
point of being overpriced.

Antennas for 2.4 GHz could be dishes or helices.  I would guess that
even the "lossy" 1" PVC "special" helix antennas will work fb.  This would 
be, er... free or a buck or two to construct.  (I had wire and PVC on hand, 
so for me it was free)

Putting power out at 1269 will still be somewhat costly, but I would
assume that P3D will be configured to have the 435 MHz uplink receiver
on as well.  (I picked up a Mode-L SSB unit for $150 at a hamfest,
due to the individuals lack of faith in AMSAT)  Even a 70 cm and 2.4 GHz 
antenna would be better than a 2m/70cm combo for reasonable size.

Doppler isn't too much of a concern at apogee either.. remember doppler is 
motion relative from the satellite to the observer.. since the satellite is 
in a fairly constant position in the sky at apogee, the doppler is not going 
to be that bad-- even at 2.4 GHZ.  Yeah,
maybe at 10 GHz.. but thats why we are experimenting with this now.

The argument for going with the microwaves is that if they catch on,
the next AMSAT Phase 3 satellite could be as functional as P3D, and
not weigh 1400 lbs, and not have to have LARGE 2m antennas on it.
We can pick what "modes" worked best on P3D, and add other experiments to 
continue the technological advancements for later satellites.

Why do so few commercial satellites use VHF/UHF anymore?  Think about
it.  Microwaves allow greater bandwidth to be used, and are just
as "line-of-sight".  Path loss is greater, but antenna gain (with smaller 
antennas) can be made to make up for that, plus some.

The sacrifice is that the ground stations will have to adapt.  But
as others have stated:  P3D will be around for (god willing) 10 years.

I do not understand why so many are so closed minded about positive
technological change.  We should all be excited about the new
opportunities P3D will give us.  And yes, the ragchewers and contest
people who are not techincal will still have "Mode-B" for
awhile (assuming they can hear through the local noise on 2m-- and Jon, I 
only moved from the Chicago area 2 1/2 years ago, and back then I had a 
fairly hard time receiving AO-13.  Preamps always got
saturated by pagers, etc... Admittedly Cedar Rapids is better..).

Fred W0FMS

>From: Jon Ogden <na9d@mindspring.com>
>To: "Frederick M. Spinner" <fspinner@hotmail.com>, <amsat-bb@amsat.org>
>Subject: Re: [amsat-bb] P3D information
>Date: Wed, 11 Oct 2000 23:40:59 -0500
>on 10/11/00 9:42 AM, Frederick M. Spinner at fspinner@hotmail.com wrote:
> > All perpetuating old modes is going to do for AMSAT is keep
> > people from using the birds.  It used to take a fairly substantial
> > antenna setup and a moderate amount of power (10W on 70cm usually didn't 
> > it) to work AO-13 at apogee (or for most of its pass),
> > and that kept many from ever using the bird.
>Interesting.  I've worked AO-10 at apogee with about 10 to 20 Watts.  I 
>a hard time believing AO-13 was worse than AO-10.
>Then again, I'm not an alligator.
>Jon Ogden
>NA9D (ex: KE9NA)
>"A life lived in fear is a life half lived."

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