[amsat-bb] Re: Why do the amsats get more and more complex?

John B. Stephensen kd6ozh at comcast.net
Wed Sep 20 12:40:43 PDT 2006

We lost 1215-1240 MHz to GPS and were required to accept interference from 
ISM devices on 2400-2450 MHz 25 years ago so further restrictions are 
possible in the future.



----- Original Message ----- 
From: <sco at sco-inc.com>
To: <amsat-bb at amsat.org>
Sent: Wednesday, September 20, 2006 18:30 UTC
Subject: [amsat-bb] Re: Why do the amsats get more and more complex?

Looks to me that only the commercial service will
possibly interfere with the Ham L band uplink.
The open service signals will not be in the L
band. Even then the Commercial service will be
broadcast in three bands, only one of those is in
our ham band. I would therefore assume if the
commercial receiver was having interference on
the CS channel (our L band) that it would switch
over to one of the other TWO Open channels to
gets its info. See the specs below. So what is
the problem. Are we afraid that we might offend
the Europeans if we are on one of their three
channels? Sounds to me like Europe is building
this system so they will have their own GPS if
they decide to go to war with us. I hope they
build it such that the Islamic Fascists can't use
it to deliver bombs and missiles.


At 02:05 PM 9/20/2006, John B. Stephensen wrote:
>Unfortunately, the Gaileo downlink covers
>1258-1299 MHz, the first satellite has been
>lanched and the satellites in the constellation
>will be on over the entire world. Our uplink
>antennas have sidelobes that are 10-20 dB down,
>so a 1 kW EIRP SSB uplink results in 10-100 W
>radiated towards terrestrial receivers. A 256
>kbps uplink would require 16 kW EIRP and be 0.5-1 MHz wide.
>P3E has a second L receiver tuned to a null in
>the Galileo signal (there is only one null in
>the 1260-1270 MHz band) but no one knows if this
>will help. SSB users can move to the U uplink if
>L is a problem. However, this only works for
>narrowband signals. A wideband uplink won't fit
>in the null and can't move down in frequency.

There will be four different navigation services available:
    * The Open Service (OS) will be free for
anyone to access. The OS signals will be
broadcast in two bands, at 1164-1214
<http://en.wikipedia.org/wiki/MHz>MHz and at
1563-1591 MHz. Receivers will achieve an accuracy
of <4 m horizontally and <8 m vertically if they
use both OS bands. Receivers that use only a
single band will still achieve <15 m horizontally
and <35 m vertically, comparable to what the
civilian GPS C/A service provides today. It is
expected that most future mass market receivers,
such as
navigation systems, will process both the GPS C/A
and the Galileo OS signals, for maximum coverage.
    * The encrypted Commercial Service (CS) will
be available for a fee and will offer an accuracy
of better than 1 m. The CS can also be
complemented by ground stations to bring the
accuracy down to less than 10 cm. This signal
will be broadcast in three frequency bands, the
two used for the OS signals, as well as at 1260-1300 MHz.
    * The encrypted Public Regulated Service
(PRS) and Safety of Life Service (SoL) will both
provide an accuracy comparable to the Open
Service. Their main aim is robustness against
jamming and the reliable detection of problems
within 10 seconds. They will be targeted at
security authorities (police, military, etc.) and
safety-critical transport applications
(air-traffic control, automated aircraft landing, etc.), respectively.

In addition, the Galileo satellites will be able
to detect and report signals from COSPAS-SARSAT
in the 406.0-406.1 MHz band, which makes them a
part of the
Maritime Distress Safety System.

>----- Original Message ----- From: <sco at sco-inc.com>
>To: <amsat-bb at amsat.org>
>Sent: Wednesday, September 20, 2006 16:16 UTC
>Subject: [amsat-bb] Re: Why do the amsats get more and more complex?
>>Galileo (if it is ever built  and launched and worked) would just be
>>over Europe, right? That would leave the rest of the world the
>>ability to use our L band uplink, right? If we hams are using a dish
>>pointed at the sky with a narrow bandwidth how is that going to
>>interfere with ground receivers some distance from us? We would be
>>smart enough to not have the Eagle uplink on the same freq, right?
>>And we would design Eagle such that we could (from ground control)
>>move the Eagle receive freq away from any potential conflict with
>>Galileo, right? And Eagle would be in orbit and operational long
>>before Galileo, right? And Galileo receivers on the ground will have
>>the ability to cut out any possible interference from us, right?
>>Seems to me that we are planning to give up the L band (as an uplink)
>>based on a lot of bad assumptions.
>>Les W4SCO
>>>The answer is in two parts. First, an L-band ground antenna would be too
>>>large to disguise as a TVRO dish. Second, there is fear that over the
>>>lifetime of Eagle that L-band could become unavailable, particularly in
>>>Europe, if the Galileo system is deployed.  Galileo would be a primary
>>>service and Ham transmissions would likely interfere with low cost
>>>commercial receivers.
>>>I don't wish to debate these points. I'm just telling you the reasoning 
>>>went into not choosing L-band. I assure you that every possibility was
>>>considered. Lists were created and discussed on each alternative.
>>>AMSAT LM2232
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