[amsat-bb] S-Band and Eagle -- User Inputs to the Design Process

Bruce Rahn brahn at woh.rr.com
Fri Sep 8 17:49:40 PDT 2006

I've been following the thread regarding the decision to drop S-Band 
downlink capabilities from Eagle with great interest.  As usual, the 
factions are clearly falling into two groups--the "techies" and the 
"user community".  However, before getting into my discussion on these 
two groups, I'd like to share a little research I did on peer reviewed 
work which has been done regarding an S-Band spectrum survey.

I ran across an interesting paper titled "Measurements of Man-Made 
Spectrum Noise Floor" (NASA/CR-2004-213551 November 2004) based on work 
sponsored by NASA and the Department of Transportation and may be found at


Of interest to AMSAT members is Section 2, "L, S, and ISM Bands 
Survey".  This section is an expanded version of the paper titled "L and 
S Bands Spectrum Survey in the San Francisco Bay Area" presented at the 
IEEE PLANS 2004 conference and may be found at


I encourage all interested parties to download and review these two 
documents!  This is peer reviewed science--not casual observations or 

The papers support the arguments presented by the Eagle team that the 
S-Band noise floor is 14 to 29 dB higher than thermal noise due to all 
the terrestrial emitters operating in this spectrum.  However, it is 
very noteworthy, and must be pointed out, that all of these measurements 
were done with antenna systems pointed at the horizon!  This forced me 
to ask the question of what does the spectrum look like at 5, 10, 15, 30 
etc. degrees above the horizon?   More on this later.

In a recent email, Dr. Clark encourages folks to make spectrum surveys.  
Conceptually, this is a wonderful idea, but I seriously doubt many of us 
have the resources at hand to duplicate the measurement set up  
described in the above references.  Without some form of a standardized 
measurement system the results obtained by "amateur observers" really do 
not hold water!  It's imperative to have a calibrated measurement system 
along with a uniform methodology of taking measurements for them to have 
any true meaning.  Otherwise we are back to subjective interpretation of 
the results.

In another recent email to this list, Dr. McGwier provided us an 
EaglePedia link to the meeting minutes of the San Diego meeting.  Thanks 
for this information Bob...it may not be ready for prime time, but it 
sure was interesting!

It is with concern I noted that among the list of attendees, they were 
all "techies".  Not a single name stuck out as a representative of the 
"USER community".  This is sad!  Years ago Boeing started bringing 
aircraft users into the design process by having them attend and 
actively participate in design reviews.  As a result, Boeing has 
produced better aircraft which have received much higher marks from the 
users because their concerns were addressed during the design process. 
Google something to the effect of 'user involvement in the design 
process' and you will find a wealth of information on how to accomplish 
this as well as how successful it has been to countless concerns in 
addition to Boeing.

 From the outcry of AMSAT satellite users on this list, one can clearly 
see that many feel they are being ignored.   And while I haven't been 
active on a bird in over 10 years, I have to concur with their 
feelings.  EaglePedia is a wonderful idea, those involved in it are to 
be commended, but sadly, it provides information to the users AFTER the 
decisions have been made.   AMSAT leaders...now is the time to actively 
bring users into the design process.  There are multiple voices out 
there with good input waiting to be heard!  It is too late after the 
"techie" decisions have been made.

Back to the spectrum survey and the fact data was only measured at the 
horizon.  Wouldn't it be interesting to have data at other elevation 
cuts?  Perhaps we would find that the noise level is acceptable 60 to 75 
percent of the time (this is a pure assumption for the sake of 
discussion).  Would the user community be happy with this vs. horizon to 
horizon coverage?  Would it be acceptable to the user community to 
employ a directional antenna to achieve this coverage?  Given a 
trade-off between a whole new microwave station vs. antenna/tracking 
improvements, which way would the users want to go?  You have to involve 
the users to get the answers!

And how about this...how about adaptive antennas and null steering at 
the ground station to deal with this noise problem?  15 plus years ago 
when I looked at this it was out of the question in terms of cost for 
the average ham to implement.  But oh how technology has changed with 
time.  Give me a seven element S-Band array with a little hardware and 
software and I stand a good chance of nulling out six sources of 
terrestrial interference.  Enough?  Who knows...but without an S-Band 
downlink few will have the inclination to explore this fascinating area 
of technology at the ham radio level!  Are we throwing out the baby with 
the bath water by ruling S-Band out on Eagle?  I strongly think so.

We all are subjected to interference in one form or another...be it from 
your neighbor's cordless phone to power line interference to junk 
transmitters in the commercial sector.  There are solutions...not always 
easy ones, but there are solutions.  You never find them unless you try.

In closing, AMSAT has made some wonderful steps forward with EaglePedia 
but the organization needs to take this one step further.  You have to 
actively involve the user community in the design process by including 
them in design reviews in real-time, not after the fact. 

Officers, board of directors, and AMSAT members...ask yourself one 
simply question and answer it please...why does AMSAT have such a low 
retention rate of members?  I personally believe it is because the 
membership in general feels they have no say in matters and their voices 
are not heard.   You want more satellites (numbers and performance) you 
have to grow the membership base.  A vital step is in membership 
RETENTION!  Listen to the members...they might stick around for decades 
vs. a year or two.

Regards -- Bruce

Bruce Rahn

Wisdom has two parts:
1.  having a lot to say; and
2.  not saying it!

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