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

23 Sep 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 
high-resolution images.
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.
73,
John
KD6OZH
----- Original Message ----- 
From: sco@sco-inc.com
To: "amsat bb" amsat-bb@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 
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
apogee.
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
uplink.
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.
73,
John
KD6OZH
----- Original Message -----
From: "Bruce Rahn" brahn@woh.rr.com
To: "John B. Stephensen" kd6ozh@comcast.net
Cc: K3IO@verizon.net; "AMSAT BB" amsat-bb@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:

having a lot to say; and
not saying it!

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