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
http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/vwapj/smse00205-novate...
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
http://waas.stanford.edu/~wwu/papers/gps/PDF/DoIEEEPLANS04.pdf
I encourage all interested parties to download and review these two documents! This is peer reviewed science--not casual observations or opinions.
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