[amsat-bb] Re: Galileo interference on L band

John B. Stephensen kd6ozh at comcast.net
Fri Sep 22 16:36:17 PDT 2006

Mode B (U/V) and J (V/U) were the first and second most popular modes for 
the membership and 65% were interested in a digital phase 3 satellite. SSB 
(class 0) and the digital mode that fits (class 1) will be available on U/V. 
V/U is plagued by interference in some areas of the world.



----- Original Message ----- 
From: "Bill Ress" <bill at hsmicrowave.com>
To: <brahn at woh.rr.com>; "John B. Stephensen" <kd6ozh at comcast.net>
Cc: "AMSAT BB" <amsat-bb at amsat.org>; <K3IO at verizon.net>
Sent: Friday, September 22, 2006 23:02 UTC
Subject: RE: [amsat-bb] Re: Galileo interference on L band

> To All,
> Finally, leaving Galileo "off the table" right now, I believe Bruce's post
> gets to the core of what is causing the concern among members. I would 
> hope
> the Board and the design team gives Bruce's questions due reflection.
> The designers and the Board must look to the users for their direction. If
> users want 145 up and 29 down, and that will satisfy their satellite
> communications needs, then by golly that's what you put in space even 
> though
> it isn't technically cute or fashionable. They're the main source of
> donations (I think unless there are a few well heeled donors with deep
> pockets driving the ship). In short the Board should be working at the
> behest of the membership.
> Where does all this high duty cycle, high bandwith 256 kbps digital video
> and text messaging come from anyway? Are we trying to be a cell phone
> company in space? It neat for sure, but what percentage of our members can
> make the technical and financial investment for this specialized mode. 
> (This
> mode wasn't even proposed in the 2004 survey - as read it)
> How can I put this nicely? Well, I can't so here goes.
> AMSAT should be building satellites that meet majority user requirements 
> not
> build satellites for the technical ego's of a few.
> Ouch - there I said it!
> Bruce's suggestion for "user advocates" is good but the organization might
> well find that it is just another impediment to doing their design work. 
> But
> no need! The user's spoke in 2004. Perhaps a new user survey is in order -
> though judging from the comments on the -bb, the opinions have not likely
> changed.
> Regards...Bill - N6GHz
> -----Original Message-----
> From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org]On
> Behalf Of Bruce Rahn
> Sent: Friday, September 22, 2006 2:28 PM
> To: John B. Stephensen
> Cc: AMSAT BB; K3IO at verizon.net
> Subject: [amsat-bb] Re: Galileo interference on L band
> John B. Stephensen wrote:
>> Part of the concern about using L as the primary digital uplink is the
>> fact that the ground stations will be high duty cycle emitters. BPSK
>> has a very low crest factor and one of the uses for a 256 kbps link is
>> streaming video, so it will be very much like an ATV repeater. Given
>> the equatorial orbit, Eagle will also be closer to the horizon than
>> previous amateur HEOs.
>> Even a restriction similar to the one in place for U uplinks in areas
>> of the U.S. (1 kW EIRP) would make high-speed uplinks unavailable.
> John,
> Thank you for bringing this point to my attention...through my neglect
> of things I have lost track of the dominance the digital mode has taken
> in this project.  You are correct that this signal format is a high duty
> cycle one.  My thoughts of where Eagle was heading have been more
> aligned with the desires of the membership expressed in the survey
> results presented in the September/October 2004 issue of "The AMSAT
> Journal".
> I'm going to ask some hypothetical questions here which I really don't
> expect you or anyone to answer.  They are more food for thought than
> anything else.
> -  As part of the system engineering process, were other bit rates and
> modulation schemes considered which would mitigate potential
> interference problems?
> -  What percentage of the user base (AMSAT-NA members) would be
> disenfranchised if digital video were eliminated because of its high
> duty cycle requirements and the potential for causing interference to
> other spectrum users?
> -  In the aforementioned survey results, the surveyed members indicated
> their highest preference was for analog modes followed in second place
> by digital.  Has the user mindset shifted to digital over analog?  If
> not, or unknown, are the spacecraft resources being fairly partitioned
> and allocated to support analog users?  What percentage of the user
> community will be using digital video and text messaging?
> In a private exchange with Mr. Sanford, I expressed my concern that the
> user community was not being represented by a strong 'user advocate' at
> critical design meetings.  'Designers are not users and users are not
> designers' but both camps must be fairly represented to achieve harmony
> and consensus between the two.  Bringing a strong 'user advocate' into
> the design process would be a win-win situation for both the user
> community as well as the design community.  Users would feel someone is
> directly addressing their operational concerns and the 'user advocate'
> could be the one defending decisions rather than occupying the time of
> the designers in addressing these concerns.
> I believe in the 20 plus years I have been an AMSAT member history has
> demonstrated that the 'if we build it they will come' approach has not
> worked well.  Had it been successful, the organization would have more
> resources in terms of members and dollars than we could deal with.
> Respectfully -- Bruce
> --
> Bruce Rahn
> Wisdom has two parts:
> 1.  having a lot to say; and
> 2.  not saying it!
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