I rarely post to this list but I hope you will accept my apologies 
for doing so on this topic.

At 05:31 PM 9/7/2006, Matt Ettus wrote:

  

I have a few problems with this.

1 - It has bad selection bias.  Amateurs who are already on satellites
and who use S-band downlinks are the ones who don't have problems with
interference.  If they had interference, they wouldn't be on those
bands.
    

This is IMHO a very bad assumption.  If this was a problem with AO-40 
or AO-51 (since the assumption is the problem grew expotentially 
since 2003) then I think we would have heard volumes about it.  We 
haven't.  I would be the first to defend that AO-51 is not the best 
example to use, but I swept my yagi and downconverter around 360 
degrees with my spectrum analyzer attached.  The spikes were s1 or 
below.  It's not a calibrated measurement, but I'd have to side with 
the "this isn't a problem" folks.  So I feel strongly more tests are needed.

  

Additionally, people currently on satellites tend to be those
with lots of space for big dishes.
    

I live in a townhouse - this is again a bad assumption.  I work AO-51 
with a Yagi for 2.4G.  If the wind conditions here in San Mateo are 
light (which they generally aren't) I might put put up a 60CM dish, 
but generally I won't.  Even with the Yagi - WiFi is not a problem.

  

 The point here is to open this up to
people who won't, and would have more interference problems, since they
live in denser areas and can't put up big dishes with lots of
directional gain.
    

San Mateo has almost a million people in a 12 mile radius.  I get no 
little inteference in the lower S band, and only a very small amount 
of popping (that my DSP removes completely) in the upper S band.  So 
I personally need more convincing that this isn't a problem.  At 
worse we may have to convince our members to buy better 
downconverters or add on notch filters so that their wideband 
downconverters don't suck up noise from outside the band.  But 
telling people to get a filter isn't a big inconvenience.  It's been 
done before.

  

2 - Anecdotal "evidence" is pointless, especially since it is 5 years
old.  WiFi is a lot more popular now than it was 5 years ago.
    

Matt, I don't want to seem confrontational, but so far all I've seen 
is anecdotal eveidence from the Eagle team.  I will admit I don't 
read everything, but I do read things more closely when I see things 
like camera shots from spectrum analyzers that are real 
experiments.  I haven't seen it.

It is important to provide empirical data.  I have a very open mind, 
but so far the only thing I've seen are predictions of impending doom 
and statistics, not hard data.

  

3 - Could you justify putting up an X million dollar satellite that uses
a band which is questionable at best, just because some complainers who
don't actually volunteer to do anything say that it works for them?
    

I think this is a very good question - so if that is the argument, 
why would you put up a mode U/V transponder?  It's as usable as mud 
in a gas tank.

  

4 - Why should we have to justify why we're not using a band?
    

There are several reasons.  The first is because we have spectrum 
allocated there, and if we don't use it we simply lose it.  In the 
future we may need to rely upon it.

The other reason is because the people who bought into the technology 
5-10 years ago have an investment that hasn't yet been fully 
realized.  I don't want to go down the road questioning the judgement 
of people who told our customer base to go down the road, but if it 
was flawed we haven't told people we are sorry.  It's also why none 
of the commercial broadcasters cut off analog TV transmissions when 
the FCC set the 2006 deadline.  People hang on to technology.

  

 As we
agreed at the SD meeting, we are looking at providing _services_ and the
best way to do that, not how to best make use of old hardware, which
wouldn't be usable anyway.
    

I wasn't invited to that meeting, but can you tell me why you don't 
think it wouldn't be usable?  I think that is a very bad assumption.

  

X-band is usable too.  Why isn't anyone
asking us to justify not using it?
    

I'm not an expert at that level of microwave technology, but I think 
that the biggest hurdle (and I could be slammed here) is that if we 
were to try to launch an X-Band satellite I'm not sure the baseband 
oscillator technology would be stable in space at a price we can 
afford.  Rick can comment on that - he's the GPS expert and I'm 
commenting with only terrestrial experience. But putting a GPS 
corrected clock for X-Band stabilization is something we haven't 
tried before.  However, perhaps we should, and I think the membership 
would get behind that experiment.

73,

Emily

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