[amsat-bb] Re: Galileo interference on L band
John B. Stephensen
kd6ozh at comcast.net
Fri Sep 22 17:16:20 PDT 2006
256 kbps MPEG4 video is not quite TV broadcast quality but quite good. I'll
send you a file separately. There are many hams that operate ATV and this is
the only way to provide that mode nationally and internationally. The other
impetus for 256 kbps is that NGOs need it for emergency data communications.
Another use could be to provide an SSTV-like service, but with
RTTY is discouraged on linear transponders because of the low crest factor
and PSK31 has problems with doppler. The purpose of the class 1 digital
service is to provide a PSK31-like service with small omnidirectional
antennas, like M2 eggbeaters.
I don't remember the DXCC rules for satellites, but I'm sure that they are
on the ARRL web site.
----- Original Message -----
From: <sco at sco-inc.com>
To: "amsat bb" <amsat-bb at amsat.org>
Sent: Friday, September 22, 2006 23:19 UTC
Subject: [amsat-bb] Re: Galileo interference on L band
> 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.
> Les W4SCO
> At 06:40 PM 9/22/2006, John B. Stephensen wrote:
>>The digital mode is not dominant as Eagle is to provide simultaneous
>>and digital service. I don't see that using U as the primary uplink 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
>>we think that it will attract more members to pay for these satellites.
>>intent is to support 3 digital transponder bit rates - approximately 50
>>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
>>of the orbit with smaller antennas and less power than we need now for
>>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!
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