[amsat-bb] Re: Galileo interference on L band
sco at sco-inc.com
Fri Sep 22 16:19:42 PDT 2006
will this be like Slow Scan TV? Otherwise for passing video we have
the internet which is much more reliable and easier to use. A HEO sat
advantage is to work DX, unlike a LEO sat. Will we be able to operate
RTTY and Psk31 via Eagle? If so then it might be a nice way to work
on DXCC Digital (RTTY & Psk31) awards. But can we use satellite
contacts as credit for DXCC awards? Is there a DXCC video award that
exists now or in the future?
I am sure Eagle will be fun for many users to use in maybe 5-10
years. I certainly see no chance of us building and launching it in
less than 5 years. After that I think a more practical goal would be
to launch one HEO every 10 years. Don't know about the rest of you
but our property taxes are going up a lot here. One ham friend's
house jumped from $5,500 last year to $6,000 this year.
At 06:40 PM 9/22/2006, John B. Stephensen wrote:
>The digital mode is not dominant as Eagle is to provide simultaneous analog
>and digital service. I don't see that using U as the primary uplink and and
>making L the secondary uplink for the linear transponder is a big problem.
>P3E designers made the same choice by having the L antenna work only near
>The digital service will be used by those AMSAT members interested in it and
>we think that it will attract more members to pay for these satellites. The
>intent is to support 3 digital transponder bit rates - approximately 50 bps,
>4800 bps and 256 kbps -- as described in the San Diego meeting document on
>EaglePedia. 4800 bps allows for digital voice uplinks and downlinks over 75%
>of the orbit with smaller antennas and less power than we need now for SSB.
>No one could come up with a modulation scheme (even SSB) that would
>eliminate the potental for interference on L band as the power spectral
>density of the uplink signal is so much higher than the Galileo downlink
>signal. This is why another band was recommended as the primary digital
>As far as I can tell, AMSAT has put the linear transponders that the
>majority of its members wanted on each phase 3 satellite. Adding digital
>services that the rest of the world is using seems likely to attract more
>members than continuing with the same old strategy.
>----- Original Message -----
>From: "Bruce Rahn" <brahn at woh.rr.com>
>To: "John B. Stephensen" <kd6ozh at comcast.net>
>Cc: <K3IO at verizon.net>; "AMSAT BB" <amsat-bb at amsat.org>
>Sent: Friday, September 22, 2006 21:27 UTC
>Subject: Re: [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!
>Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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