[amsat-bb] Re: [Fwd: S-band on Eagle]

Thu Sep 7 22:10:00 PDT 2006

Jim replied....

>>>We validated interference predictions with measurements
that have been taken.  The conclusion is that S-band is marginally
useful as a downlink today (unusable in many locations), and by the time
Eagle is launched, and through it's lifetime, will be unusable<<<

Roger (WA1KAT) asks...

Is it possible to provide the locations where your measurements were taken,
what prediction criteria were used, and support your statement that the s
band downlink "is marginally useful as a downlink today (unusable in many
locations)"

It seems that actual users of S Band do not support your research and
question your empirical methods.

Could you also provide us with your experience with S Band satellites and
your physical location?

Many thanks!

Roger
WA1KAT

----- Original Message ----- 
From: "Jim Sanford" <wb4gcs at amsat.org>
To: <amsat-bb at amsat.org>
Sent: Thursday, September 07, 2006 10:53 PM
Subject: [amsat-bb] [Fwd: S-band on Eagle]

>
>
> -------- Original Message --------
> Subject:    S-band on Eagle
> Date:   Thu, 07 Sep 2006 21:40:37 -0400
> From:   Jim Sanford <wb4gcs at amsat.org>
> To:     amsat-bb at amsat.org
>
>
>
> Ladies and gentlemen:
>
> I have been reading the comments regarding the Eagle S-band downlink
> decision.  I herewith respond to some.
>
> All along, the Eagle project has put a premium on hard science, rigorous
> peer review, and dispassionate analysis.
>
> All along we knew there might or would be some changes to what we've
> been planning.
>
> With several other issues on the move or decided, we took a few days in
> late June to hammer out, based on science, the transponder situation.
> We did multiple, independent link analyses, and all came to the same
> conclusion.  We validated interference predictions with measurements
> that have been taken.  The conclusion is that S-band is marginally
> useful as a downlink today (unusable in many locations), and by the time
> Eagle is launched, and through it's lifetime, will be unusable.
>
> Personally, I do not like this decision.  I have S-band equipment that I
> was looking forward to using.
>
> Personally, I can live with this decision, and defend it to myself, let
> alone anyone else, because I am convinced that it is technically sound.
>
> As one of you commented this evening, AO-40 wasn't exactly a rock
> crusher on S-band.  It worked, and adequately, at least on CW, but was
> not great.  As I reflect on my personal AO-40 experiences, I now
> understand that there are 2 reasons for my disappointment.  Local noise
> was one, and transponder distortion was another -- the latter will be
> corrected by SDX.  S-band on AO-40, by necessity not choice, got many of
> us out of our comfort zones and convinced us that microwaves really
> aren't that hard.  Let's enter the realm of S up and C down with that
> same realization.
>
> REMEMBER THAT AMSAT IS DEVELOPING THE GROUND STATION ALONG WITH THE
> SPACE SEGMENT.
>
> You will not be left on your own to develop ground equipment.  You will
> not be asked to mortgage your house; affordability by the masses is a
> key component of the design for the entire system.
>
> Comparison with AO-51 is an "apples and oranges" thing.  The path losses
> are much different.  FM is very unlike CW/SSB or wideband digital
> modes.  Remember that a goal of the Eagle system is that everything is
> on all the time.  No more matrix switches, no more schedules.  We need
> up and downlinks to be useful throughout the entire orbit.
>
> Why did we "regress" to U/V?  For one reason, many of you asked for it,
> and some of us worked hard to somehow incorporate that capability in
> response to member's desires.  The foot in the door was the utility of a
> V-band beacon in case everything else goes sour.  The forcing function
> was as follows.  A goal of Eagle has always been some kind of hand-held
> or jump bag portable ground station capability for entry into the
> emergency area while the tsunami waters are receeding and the hurricane
> winds are down to gale force.  Many of us thought we could take
> advantage of the gain in small antennas to do this on the microwaves.
> Rigorous link analysis led us to the conclusion that the best place to
> do this is U/V -- both from a RF/DC power perspective, and from a link
> standpoint.     This leads to the digital and "traditiona"l transponder
> package for U/V, implemented in SDX.
>
> Why not also include a (switchable) S-band downlink in parallel with the
> V-band?  Remember, no switches.  Also, we run into an antenna space
> problem.  We've already increased the size of the spacecraft from where
> we started, and for many reasons, do NOT want to build something as
> large as AO-40.
>
> A couple of you have commented this evening that perusing EaglePedia has
> not revealed the details of the decisions.  That is because, while Bob
> McGwier (N4HY) and I have been working on the report of the meeting, it
> is not public.  We've been working hard on it since June, in and around
> other AMSAT, ham radio, and life events.  Shortly after I push send on
> this message, I'll begin my final look at that document prior to public
> release.
>
> Before I go spend time with the spousal unit TONIGHT, I will finish it
> and publish it.  I will send an announcement on the amsat-bb that it is
> public.  To read the report, go to the EaglePedia main page, and select
> project index.  From there, select Team and Meetings, and there will be
> several options, not all public.  The San Diego meeting minutes will be
> obvious and public.
>
> Several of you have commented, "If S-band is unusable, why is it flying
> on P3E?"  Fair question, but I can't answer for AMSAT-DL.  I DO know
> that the P3E system design is considerably older and farther along than
> Eagle.  Eagle design decisions were made based on the best information
> in June of 2006.
>
> Aspects of this discussion have been worthy of /dev/null.  More aspects
> of this discussion have raised valid points and reasonable questions,
> deserving of response, which is why I've been composing this note for
> the last four hours or so.
>
> A few have raised the old allegation of the builders doing what they
> want, without regard to users needs.  This is not true.  While the
> desire to advance the state of the art (part of amateur radio's
> justification for existence and allocation of valuable spectrum) leads
> to enthusiasm and study of potentially useful new techniques, this
> desire had no impact on our analysis-based decisions.  We started with
> requirements and services, and explored what would deliver.
>
> I thank all of you for your interest and support.  Your Eagle team is
> working hard to develop a system that will serve our needs, as well as
> advance the state of the art.  As promised, we are making decisions
> based on sound, peer-reviewed science, not anybody's opinions or desires.
>
> Please read the report, study the spreadsheets, download the excel file
> and play with it.  If you can, make your own measurements and put those
> numbers into the spreadsheet.  I think you'll understand how these
> decisions were reached.
>
> After contemplating the report, send me your questions.  I'll either
> respond or forward to he who can best respond.  Another fundamental
> tenet of the Eagle project is openness, so you have a right to a
> response to a rational question.  Please recognize that we're volunteers
> too, and subject to the realities of day jobs, families, and a real
> life.  Response may not be instantaneous.
>
> Thanks again and very 73,
>
> Jim
>
> James A. Sanford, PE
> Eagle Project Manager
> wb4gcs at amsat.org
>
>
>
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