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Re: Mode B vs. Mode S



Yup, I agree about the omni issue and the 2m tape measure as well.  If 
there's room for the TX and power budget, that's a good idea.

But, as a devil's advocate, I could also argue that adding extra equipment 
in the case of a small package sat could be a problem.

Smaller sats are easier to get launch opportunities for.  Being "ballast" 
sized is good...

I think that the desire of the engineers and designers of the equipment 
REALLY wasn't/isn't to be exclusive and "kill off" membership like many have 
stated.  I think that the push to microwaves is an opportunity for AMSAT to 
be able to make smaller satellites that
can be used like AO-10, AO-13 and AO-40.

I'm kinda beating a dead horse here, but it keeps coming up.  The 
motivations to go to microwaves are because it makes sense to do so from an 
engineering perspective.  Look at DBS sats, etc.  The push there is to go to 
higher and higher freqs.  Satellite internet is pushing Ka band now. WE 
should be too.  Not because we are a "boys club" or any other political 
reason.  I suspect if AO-40 wouldn't have had it's "incident" and the 
signals were better, everyone would have had a different tune on this entire 
subject.  As I said "$hit happens".

One of the "all-eggs-in-one-basket" arguments can also work against the 
Mode-B "crowd" (for lack of a better way to put this):  Much of the expense 
and weight (expense again!) of AO-40 was in the "DC-to-Daylight" transponder 
arrangement.  On the other hand, it could be argued that having these 
multiple receivers and transmitters "saved us".  Pairing down future sats 
will require less bands be carried on the birds...

At Dayton last year when I was selling off some surplus BBQ dishes I had, I 
HAD A *HARD* time selling them!  90% of the hams told me that AO-40 blew up 
and never worked and I was trying to rip everyone off.  When I told them I'd 
heard AO-40 the day before I left, they told me I was full of crap.  I'm not 
kidding.

We can basically thank the slow reporting of the ARRL and especially the BAD 
reporting of another ham rag for that.  I think this "attitude" that the sat 
is too screwed up to be usable is the real problem with attracting new 
people to AO-40, not the reality of Mode-S, S2 only, etc.  We've surmounted 
these problems with simple and fairly inexpensive equipment so far.  And I 
personally have had a
lot of fun with this.

As a final comment, I should say there is less "political" motivation than 
is thought with this.  I think debates on the technical issues are great, 
though.

Fred W0FMS



>From: Estes Wayne-W10191 <W10191@motorola.com>
>To: amsat-bb@AMSAT.Org
>Subject: [amsat-bb] Mode B vs. Mode S
>Date: Tue, 30 Apr 2002 17:02:46 -0500
>
>Fred Spinner wrote:
>
>The Mode-S (and higher especially) equipment can be placed on smaller 
>spacecraft due to the smaller antennas, and thus should still be pursued... 
>  imagine if we could get a small sat up in a GTO, but the sat package was 
>too small for gain 2m antennas?  Would it be a political decision in this 
>case to forego a mode-B downlink?
>
>Wayne replies:
>
>In that situation, it might be logical to have an OMNI 2m antenna on the 
>OPPOSITE side of the spacecraft from the high-gain S-band antenna.  The 
>satellite could be used in Mode B near perigee, and in Mode S near apogee.
>
>Another possibility would be to have a low-gain S-band patch antenna 
>opposite from the high-gain S-band antenna.  But I like the idea of 
>multiple transmitter bands to serve more users if both transmitters 
>function in orbit, and have a greater probability that at least ONE 
>downlink will function in orbit.
>
>There should be no size consideration for a tape measure 2m omni antenna on 
>a small spacecraft.  Then we're back to debating the political and 
>technical merits of a 2m near-perigee downlink vs. a 13 cm near-perigee 
>downlink.
>
>Wayne Estes W9AE
>Mundelein, IL, USA
>----
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