-------- Original Message -------- Subject: S-band on Eagle Date: Thu, 07 Sep 2006 21:40:37 -0400 From: Jim Sanford wb4gcs@amsat.org To: amsat-bb@amsat.org
Ladies and gentlemen:
I have been reading the comments regarding the Eagle S-band downlink decision. I herewith respond to some.
All along, the Eagle project has put a premium on hard science, rigorous peer review, and dispassionate analysis.
All along we knew there might or would be some changes to what we've been planning.
With several other issues on the move or decided, we took a few days in late June to hammer out, based on science, the transponder situation. We did multiple, independent link analyses, and all came to the same conclusion. We validated interference predictions with measurements that have been taken. The conclusion is that S-band is marginally useful as a downlink today (unusable in many locations), and by the time Eagle is launched, and through it's lifetime, will be unusable.
Personally, I do not like this decision. I have S-band equipment that I was looking forward to using.
Personally, I can live with this decision, and defend it to myself, let alone anyone else, because I am convinced that it is technically sound.
As one of you commented this evening, AO-40 wasn't exactly a rock crusher on S-band. It worked, and adequately, at least on CW, but was not great. As I reflect on my personal AO-40 experiences, I now understand that there are 2 reasons for my disappointment. Local noise was one, and transponder distortion was another -- the latter will be corrected by SDX. S-band on AO-40, by necessity not choice, got many of us out of our comfort zones and convinced us that microwaves really aren't that hard. Let's enter the realm of S up and C down with that same realization.
REMEMBER THAT AMSAT IS DEVELOPING THE GROUND STATION ALONG WITH THE SPACE SEGMENT.
You will not be left on your own to develop ground equipment. You will not be asked to mortgage your house; affordability by the masses is a key component of the design for the entire system.
Comparison with AO-51 is an "apples and oranges" thing. The path losses are much different. FM is very unlike CW/SSB or wideband digital modes. Remember that a goal of the Eagle system is that everything is on all the time. No more matrix switches, no more schedules. We need up and downlinks to be useful throughout the entire orbit.
Why did we "regress" to U/V? For one reason, many of you asked for it, and some of us worked hard to somehow incorporate that capability in response to member's desires. The foot in the door was the utility of a V-band beacon in case everything else goes sour. The forcing function was as follows. A goal of Eagle has always been some kind of hand-held or jump bag portable ground station capability for entry into the emergency area while the tsunami waters are receeding and the hurricane winds are down to gale force. Many of us thought we could take advantage of the gain in small antennas to do this on the microwaves. Rigorous link analysis led us to the conclusion that the best place to do this is U/V -- both from a RF/DC power perspective, and from a link standpoint. This leads to the digital and "traditiona"l transponder package for U/V, implemented in SDX.
Why not also include a (switchable) S-band downlink in parallel with the V-band? Remember, no switches. Also, we run into an antenna space problem. We've already increased the size of the spacecraft from where we started, and for many reasons, do NOT want to build something as large as AO-40.
A couple of you have commented this evening that perusing EaglePedia has not revealed the details of the decisions. That is because, while Bob McGwier (N4HY) and I have been working on the report of the meeting, it is not public. We've been working hard on it since June, in and around other AMSAT, ham radio, and life events. Shortly after I push send on this message, I'll begin my final look at that document prior to public release.
Before I go spend time with the spousal unit TONIGHT, I will finish it and publish it. I will send an announcement on the amsat-bb that it is public. To read the report, go to the EaglePedia main page, and select project index. From there, select Team and Meetings, and there will be several options, not all public. The San Diego meeting minutes will be obvious and public.
Several of you have commented, "If S-band is unusable, why is it flying on P3E?" Fair question, but I can't answer for AMSAT-DL. I DO know that the P3E system design is considerably older and farther along than Eagle. Eagle design decisions were made based on the best information in June of 2006.
Aspects of this discussion have been worthy of /dev/null. More aspects of this discussion have raised valid points and reasonable questions, deserving of response, which is why I've been composing this note for the last four hours or so.
A few have raised the old allegation of the builders doing what they want, without regard to users needs. This is not true. While the desire to advance the state of the art (part of amateur radio's justification for existence and allocation of valuable spectrum) leads to enthusiasm and study of potentially useful new techniques, this desire had no impact on our analysis-based decisions. We started with requirements and services, and explored what would deliver.
I thank all of you for your interest and support. Your Eagle team is working hard to develop a system that will serve our needs, as well as advance the state of the art. As promised, we are making decisions based on sound, peer-reviewed science, not anybody's opinions or desires.
Please read the report, study the spreadsheets, download the excel file and play with it. If you can, make your own measurements and put those numbers into the spreadsheet. I think you'll understand how these decisions were reached.
After contemplating the report, send me your questions. I'll either respond or forward to he who can best respond. Another fundamental tenet of the Eagle project is openness, so you have a right to a response to a rational question. Please recognize that we're volunteers too, and subject to the realities of day jobs, families, and a real life. Response may not be instantaneous.
Thanks again and very 73,
Jim
James A. Sanford, PE Eagle Project Manager wb4gcs@amsat.org
Jim replied....
We validated interference predictions with measurements
that have been taken. The conclusion is that S-band is marginally useful as a downlink today (unusable in many locations), and by the time Eagle is launched, and through it's lifetime, will be unusable<<<
Roger (WA1KAT) asks...
Is it possible to provide the locations where your measurements were taken, what prediction criteria were used, and support your statement that the s band downlink "is marginally useful as a downlink today (unusable in many locations)"
It seems that actual users of S Band do not support your research and question your empirical methods.
Could you also provide us with your experience with S Band satellites and your physical location?
Many thanks!
Roger WA1KAT
----- Original Message ----- From: "Jim Sanford" wb4gcs@amsat.org To: amsat-bb@amsat.org Sent: Thursday, September 07, 2006 10:53 PM Subject: [amsat-bb] [Fwd: S-band on Eagle]
-------- Original Message -------- Subject: S-band on Eagle Date: Thu, 07 Sep 2006 21:40:37 -0400 From: Jim Sanford wb4gcs@amsat.org To: amsat-bb@amsat.org
Ladies and gentlemen:
I have been reading the comments regarding the Eagle S-band downlink decision. I herewith respond to some.
All along, the Eagle project has put a premium on hard science, rigorous peer review, and dispassionate analysis.
All along we knew there might or would be some changes to what we've been planning.
With several other issues on the move or decided, we took a few days in late June to hammer out, based on science, the transponder situation. We did multiple, independent link analyses, and all came to the same conclusion. We validated interference predictions with measurements that have been taken. The conclusion is that S-band is marginally useful as a downlink today (unusable in many locations), and by the time Eagle is launched, and through it's lifetime, will be unusable.
Personally, I do not like this decision. I have S-band equipment that I was looking forward to using.
Personally, I can live with this decision, and defend it to myself, let alone anyone else, because I am convinced that it is technically sound.
As one of you commented this evening, AO-40 wasn't exactly a rock crusher on S-band. It worked, and adequately, at least on CW, but was not great. As I reflect on my personal AO-40 experiences, I now understand that there are 2 reasons for my disappointment. Local noise was one, and transponder distortion was another -- the latter will be corrected by SDX. S-band on AO-40, by necessity not choice, got many of us out of our comfort zones and convinced us that microwaves really aren't that hard. Let's enter the realm of S up and C down with that same realization.
REMEMBER THAT AMSAT IS DEVELOPING THE GROUND STATION ALONG WITH THE SPACE SEGMENT.
You will not be left on your own to develop ground equipment. You will not be asked to mortgage your house; affordability by the masses is a key component of the design for the entire system.
Comparison with AO-51 is an "apples and oranges" thing. The path losses are much different. FM is very unlike CW/SSB or wideband digital modes. Remember that a goal of the Eagle system is that everything is on all the time. No more matrix switches, no more schedules. We need up and downlinks to be useful throughout the entire orbit.
Why did we "regress" to U/V? For one reason, many of you asked for it, and some of us worked hard to somehow incorporate that capability in response to member's desires. The foot in the door was the utility of a V-band beacon in case everything else goes sour. The forcing function was as follows. A goal of Eagle has always been some kind of hand-held or jump bag portable ground station capability for entry into the emergency area while the tsunami waters are receeding and the hurricane winds are down to gale force. Many of us thought we could take advantage of the gain in small antennas to do this on the microwaves. Rigorous link analysis led us to the conclusion that the best place to do this is U/V -- both from a RF/DC power perspective, and from a link standpoint. This leads to the digital and "traditiona"l transponder package for U/V, implemented in SDX.
Why not also include a (switchable) S-band downlink in parallel with the V-band? Remember, no switches. Also, we run into an antenna space problem. We've already increased the size of the spacecraft from where we started, and for many reasons, do NOT want to build something as large as AO-40.
A couple of you have commented this evening that perusing EaglePedia has not revealed the details of the decisions. That is because, while Bob McGwier (N4HY) and I have been working on the report of the meeting, it is not public. We've been working hard on it since June, in and around other AMSAT, ham radio, and life events. Shortly after I push send on this message, I'll begin my final look at that document prior to public release.
Before I go spend time with the spousal unit TONIGHT, I will finish it and publish it. I will send an announcement on the amsat-bb that it is public. To read the report, go to the EaglePedia main page, and select project index. From there, select Team and Meetings, and there will be several options, not all public. The San Diego meeting minutes will be obvious and public.
Several of you have commented, "If S-band is unusable, why is it flying on P3E?" Fair question, but I can't answer for AMSAT-DL. I DO know that the P3E system design is considerably older and farther along than Eagle. Eagle design decisions were made based on the best information in June of 2006.
Aspects of this discussion have been worthy of /dev/null. More aspects of this discussion have raised valid points and reasonable questions, deserving of response, which is why I've been composing this note for the last four hours or so.
A few have raised the old allegation of the builders doing what they want, without regard to users needs. This is not true. While the desire to advance the state of the art (part of amateur radio's justification for existence and allocation of valuable spectrum) leads to enthusiasm and study of potentially useful new techniques, this desire had no impact on our analysis-based decisions. We started with requirements and services, and explored what would deliver.
I thank all of you for your interest and support. Your Eagle team is working hard to develop a system that will serve our needs, as well as advance the state of the art. As promised, we are making decisions based on sound, peer-reviewed science, not anybody's opinions or desires.
Please read the report, study the spreadsheets, download the excel file and play with it. If you can, make your own measurements and put those numbers into the spreadsheet. I think you'll understand how these decisions were reached.
After contemplating the report, send me your questions. I'll either respond or forward to he who can best respond. Another fundamental tenet of the Eagle project is openness, so you have a right to a response to a rational question. Please recognize that we're volunteers too, and subject to the realities of day jobs, families, and a real life. Response may not be instantaneous.
Thanks again and very 73,
Jim
James A. Sanford, PE Eagle Project Manager wb4gcs@amsat.org
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Jim Sanford wrote
REMEMBER THAT AMSAT IS DEVELOPING THE GROUND STATION ALONG WITH THE SPACE SEGMENT.
You will not be left on your own to develop ground equipment. You will not be asked to mortgage your house; affordability by the masses is a key component of the design for the entire system.
At this point in time, is there anyway you can elaborate on the above statement? We may well not have to mortgage our homes but 'affordability" is a somewhat relative term. What AMSAT considers affordable and what I consider affordable may be two completely different things. Are we too early in the design process for you to reveal what you have in mind along the lines of ground station equipment? Possibly some type of surplus downconverter again? etc. etc. Thank you for your hard work on the project, Michael, W4HIJ AMSAT # 36017
Michael: Thanks for your interest.
Over the last year or so, we've had several numbers thrown around about cost of the ground station. It's way too early for me to be comfortable with any of them.
Here's how Jim Sanford looks at it: I spent nearly $500 for my first APRS-included handheld. I spent nearly $600 for my first mobile APRS-included rig. A year later I spend nearly as much on a mobile for the wife's car.
Were I not involved in Eagle, and presented with the opportunity to purchase or build this digital voice ground segment for similar costs, I'd do it in a heartbeat -- and I am NOT an "early adopter" that industry loves so dearly.
The Eagle team is very well aware of the "they built it, how do I use it?" syndrome. That's why we're looking at the whole system. We're avere aware of the need to keep costs low. I can not yet project what the costs will be, but I have a sense that the above numbers will be acceptable to many. If we get there I'm happy, but will press to do all we can to lower it. Remember, we're building 3 space segments, and hopefully thousands of gorund elements. If the cost comes in higher than that, I'll be pushing hard for redesign or other options, to drive cost down.
In my reading of the industry, and in my day job, I see where technology is headed. This gives me confidence in predicting that we'll deliver at a cost that many hams have already accepted for new equipment of lesser capability. It will not be a $19.95 widget. But it won't be a $5999.95 CIA device, either.
It is too early to lay out projections. At this point all I can say is what I think, listed above, and Jim Sanford's promise to do everything possible to make it affordable to the average ham. If it isn't, I won't have anyone to talk to. I geet it.
Thank you for your support and interest.
73, Jim wb4gcs@amsat.org
Michael Tondee wrote:
Jim Sanford wrote
REMEMBER THAT AMSAT IS DEVELOPING THE GROUND STATION ALONG WITH THE SPACE SEGMENT. You will not be left on your own to develop ground equipment. You will not be asked to mortgage your house; affordability by the masses is a key component of the design for the entire system.
At this point in time, is there anyway you can elaborate on the above statement? We may well not have to mortgage our homes but 'affordability" is a somewhat relative term. What AMSAT considers affordable and what I consider affordable may be two completely different things. Are we too early in the design process for you to reveal what you have in mind along the lines of ground station equipment? Possibly some type of surplus downconverter again? etc. etc. Thank you for your hard work on the project, Michael, W4HIJ AMSAT # 36017
participants (3)
-
Jim Sanford -
Michael Tondee -
Roger Kolakowski