Ok folks,
Its time for some fun ... how about we design and fly our own transponder via the amsat-bb?
I propose BBSat (sounds better than AdHocSat). This is a call for ideas of a single board transponder in cubesat form factor ... what can we put on a 10cm ^2 circuit board? FM, SDR, packet?
Initially there are only two rules ... 1) No griping 2) This is going to be an open source project
Let us know what you think right here on the -bb ...
-- 73 de JoAnne K9JKM k9jkm@amsat.org
I'll play!
On the drive home from the symposium in Atlanta, I was thinking about a cubesat with a "hybrid" voice repeater. My idea would use a 435 FM uplink because it's easy to generate power enough on the ground, and the Doppler shift moves QRM out of the uplink fast, it's FM and not picky about tuning, and there aren't any illegal telephones that work on the uplink AFAIK. We'd use a 2m SSB downlink, for a few reasons. 2m path loss is less, so given similar antennas we'll get a better downlink. SSB is more efficient than FM, and we also save power by not transmitting unless there is audio on the uplink, a squelch of sorts.
No computer on my satellite either! We'd have some sort of hardware timer that has to be reset every few days to keep the repeater running, so we could meet FCC rules on control. Maybe PL or DTMF?
Wouldn't it be neat to have one of these sitting on the shelf in case a empty spot on a PPOD became available?
73, Drew KO4MA
----- Original Message ----- From: "JoAnne Maenpaa" k9jkm@comcast.net To: AMSAT-BB@amsat.org Sent: Monday, November 24, 2008 8:40 PM Subject: [amsat-bb] BBsat Call for ideas
Ok folks,
Its time for some fun ... how about we design and fly our own transponder via the amsat-bb?
I propose BBSat (sounds better than AdHocSat). This is a call for ideas of a single board transponder in cubesat form factor ... what can we put on a 10cm ^2 circuit board? FM, SDR, packet?
Initially there are only two rules ...
- No griping
- This is going to be an open source project
Let us know what you think right here on the -bb ...
-- 73 de JoAnne K9JKM k9jkm@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
At 01:01 PM 11/25/2008, Andrew Glasbrenner wrote:
On the drive home from the symposium in Atlanta, I was thinking about a cubesat with a "hybrid" voice repeater. My idea would use a 435 FM uplink because it's easy to generate power enough on the ground, and the Doppler shift moves QRM out of the uplink fast, it's FM and not picky about tuning, and there aren't any illegal telephones that work on the uplink AFAIK. We'd use a 2m SSB downlink, for a few reasons. 2m path loss is less, so given similar antennas we'll get a better downlink. SSB is more efficient than FM, and we also save power by not transmitting unless there is audio on the uplink, a squelch of sorts.
Interesting idea, except I do have one quibble - normally when there is no signal on FM, there would be the background noise at high level. You would need to have squelch on the bird to cut the Tx power to zero.
No computer on my satellite either! We'd have some sort of hardware timer that has to be reset every few days to keep the repeater running, so we could meet FCC rules on control. Maybe PL or DTMF?
Wouldn't it be neat to have one of these sitting on the shelf in case a empty spot on a PPOD became available?
Could be neat to have a simple bird to throw up at the drop of a hat. Also there are more 2m SSB radios than 70cm ones in service down this way, so this is a goer in my book. :)
73 de VK3JED http://vkradio.com
Interesting idea. But, there are really two fundamental ways to go here.
We can go low-tech; your idea. Simple analog transponder. Keep the housekeeping logic to a minimum to conserve power, maximize reliability, and minimize cost. Clone AO-07, in effect, but with modern components.
The other direction would be to go the other way - high tech. I for one would love to see a testbed for Eagle's ACP running in a LEO satellite, focusing, say, on the low bandwidth instant messaging application. I know we can do this with APRS today, but only inefficiently. We need a testbed to prove out both the modulation schemes necessary for improving the link budget, and the protocols for supporting the many multiple communications connections that this application demands.
I have no idea if this is even possible in a Cubesat format satellite. My only visibility into Eagle was at last year's AMSAT conference in Foster City (San Francisco area), but what I saw in the presentation really underscored the tag line on the AMSAT banner hanging over the conference hall entrance. "We are rocket scientists!" (or words to that effect..)
Greg KO6TH
Date: Tue, 25 Nov 2008 13:38:03 +1100 To: glasbrenner@mindspring.com; k9jkm@comcast.net; AMSAT-BB@amsat.org From: vk3jed@gmail.com Subject: [amsat-bb] Re: BBsat Call for ideas
At 01:01 PM 11/25/2008, Andrew Glasbrenner wrote:
On the drive home from the symposium in Atlanta, I was thinking about a cubesat with a "hybrid" voice repeater. My idea would use a 435 FM uplink because it's easy to generate power enough on the ground, and the Doppler shift moves QRM out of the uplink fast, it's FM and not picky about tuning, and there aren't any illegal telephones that work on the uplink AFAIK. We'd use a 2m SSB downlink, for a few reasons. 2m path loss is less, so given similar antennas we'll get a better downlink. SSB is more efficient than FM, and we also save power by not transmitting unless there is audio on the uplink, a squelch of sorts.
Interesting idea, except I do have one quibble - normally when there is no signal on FM, there would be the background noise at high level. You would need to have squelch on the bird to cut the Tx power to zero.
No computer on my satellite either! We'd have some sort of hardware timer that has to be reset every few days to keep the repeater running, so we could meet FCC rules on control. Maybe PL or DTMF?
Wouldn't it be neat to have one of these sitting on the shelf in case a empty spot on a PPOD became available?
Could be neat to have a simple bird to throw up at the drop of a hat. Also there are more 2m SSB radios than 70cm ones in service down this way, so this is a goer in my book. :)
73 de VK3JED http://vkradio.com
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Thanks to all for a fun and engaging thread.
One idea that hasn't been floated yet, but which I believe deserves consideration, is a 10m or 15m transmitter aboard bbSat. Years before actually being able to communicate through an amateur satellite, I listened to the RS robots on 10m and 15m, and that achievement gave me the confidence to proceed. I therefore think a transponder that downlinked on these bands would be likely to 'broaden our base', and it would help keep active these, now unused, satellite bands.
I recognize that transmitting on such a long wavelength from a 10cm cube represents a technical challenge, but it would largely be a challenge of mechanical engineering, not something that would run up against the limited power budget. I also vaguely have the impression that amplifiers, etc. are more efficient in the lower frequencies, so that might be a plus. (Not to mention reduced path loss.) Perhaps the effective power out would be so low that a directional antenna would be required on the ground. In which case, I'd say it was a no-go, since that would preclude too many of the new experimenters that we'd be hoping to snare on these bands.
How about this.
1. On the satellite there's a 9600 FSK regenerating repeater. If it hears a bit, it sends a bit without any other smarts. 2m up, 440 down.
2. Also there's a clock. It puts out a tick 8 times per second.
3. For the ground stations, we design a simple TDMA system. Each user gets a time slot for transmitting into the satellite. Let me see, 9600 baud is 960 characters a second, so we break that into 8 blocks of 100 character or so every second and for up to 16 users for a 2 second time block. Enough bytes to do a small ax25 packet, or maybe we just stew up something new. Callsign + checksum + data.
3. Then we just make it a big chat room in the sky. The thing flies over, you type on your computer and then your software uses an unused time slot for sending the data. Everyone can read your message, and can chat back to you.
Ah, but how does one know that a time slot is not being used? With many stations on the ground, there is a good chance that multiple stations will pick the same "empty" slot to be theirs, and we're back to collisions.
So, this is what I was talking about when I suggested, as essentially you do, to work on a prototype of the ACP messaging system that is being proposed for Eagle. There are two significant technical challenges that I see, and the protocol used to facilitate fair and resilient access to the satellite by all the ground stations it overflies is one. Fair is making sure that everyone has an equal share of the satellite, and resilient is that as the load on the satellite goes up, the whole thing doesn't degrade to being unusable. I haven't checked, but has the Eagle team published their protocol for doing this? Perhaps we can start with that, simplifying as much as we can to make it fit the limited cubesat environment.
The other challenge is the modulation system, which will be an interesting study in engineering tradeoffs. As one poster noted, the more power you put into the electronics, the less you have for the downlink transmitter. Better modulation schemes can compensate for a lower transmit power, but if it takes more power to do that modulation, its a wonder if you come out ahead...
Greg KO6TH
Date: Wed, 26 Nov 2008 09:52:19 -0800 From: cathrynm@junglevision.com CC: amsat-bb@amsat.org Subject: [amsat-bb] Re: BBsat Call for ideas
How about this.
- On the satellite there's a 9600 FSK regenerating repeater.
If it hears a bit, it sends a bit without any other smarts. 2m up, 440 down.
- Also there's a clock. It puts out a tick 8 times
per second.
- For the ground stations, we design a simple
TDMA system. Each user gets a time slot for transmitting into the satellite. Let me see, 9600 baud is 960 characters a second, so we break that into 8 blocks of 100 character or so every second and for up to 16 users for a 2 second time block. Enough bytes to do a small ax25 packet, or maybe we just stew up something new. Callsign + checksum + data.
- Then we just make it a big chat room in the sky. The
thing flies over, you type on your computer and then your software uses an unused time slot for sending the data. Everyone can read your message, and can chat back to you.
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Greg D. wrote:
Ah, but how does one know that a time slot is not being used? With many stations on the ground, there is a good chance that multiple stations will pick the same "empty" slot to be theirs, and we're back to collisions.
For good performance, some sort of media-access control (MAC) protocol is required. Time-slotted protocols have a lot to be said for them, although some have suggested using a CDMA protocol. You could create a system that assigns time slots to active ground stations. But, if these stations are generating very bursty traffic, like voice, a lot of the uplink bandwidth may be wasted. In general, I think this is what I call a "hard problem" (i.e., we don't know how to solve it [yet], and perhaps nobody else does either).
So, this is what I was talking about when I suggested, as essentially you do, to work on a prototype of the ACP messaging system that is being proposed for Eagle.
I think this is a great idea.
Unfortunately, as far as I can tell, all development work on the Eagle and the ACP ceased several months ago. The Microwave Engineering Project (MEP) is or might become, in some vague sense, a terrestrial variant of the ACP.
http://www.delmarnorth.com/microwave/
I am hopeful that at least some of the work on the MEP will be applicable to the ACP.
There are two significant technical challenges that I see,
Actually. I think there are a quite a few technical challenges and issues...
and the protocol used to facilitate fair and resilient access to the satellite by all the ground stations it overflies is one. ... I haven't checked, but has the Eagle team published their protocol for doing this? ...
The team developing the ACP ground station made pretty much everything they wrote freely available online. [What a concept!} Unfortunately, they didn't get all that far before work ceased. See the ACP ground station Web site:
http://www.delmarnorth.com/namaste/
The other challenge is the modulation system ...
^^^^^^^^^ Another
You might look at these two documents:
http://www.delmarnorth.com/microwave/requirements/Microwave_Link_Discussion.pdf
http://www.delmarnorth.com/microwave/requirements/Microwave_Link_Analysis.pdf
-tjs
Timothy J. Salo wrote:
Greg D. wrote:
Ah, but how does one know that a time slot is not being used? With many stations on the ground, there is a good chance that multiple stations will pick the same "empty" slot to be theirs, and we're back to collisions.
For good performance, some sort of media-access control (MAC) protocol is required. Time-slotted protocols have a lot to be said for them, although some have suggested using a CDMA protocol. You could create a system that assigns time slots to active ground stations. But, if these stations are generating very bursty traffic, like voice, a lot of the uplink bandwidth may be wasted. In general, I think this is what I call a "hard problem" (i.e., we don't know how to solve it [yet], and perhaps nobody else does either).
Sounds like this could be someone's Master's or PhD thesis then.
Anyway, at the risk of looking silly, which I'm always in danger of, it might be fun to cook up something that's 'almost good enough.'.
I'm reminded a little of the ham radio HF nets, where net control calls out for 'callsign district 0', 'callsign district 1', Reserve a regular slot for 'check-ins' and then the satellite puts out a call for 'everyone to check in. If too many come in, then it asks for 'district 0', and if that's still too many, it thins it down even further. (Though somehow we'd need a way to detect a pileup versus noise. Hmm.)
Once you get a 'check-in packet' in, it then assigns you a slot to use, and your data would be 'here's my packet, and I'd also like to send another XX ticks from now'.
Give priority to packets farther in the future, so as the system overloads, a large number of low bandwidth users keep going.
If you miss your slot, you lose, and have to check in again.
Hello,
First of all congratulations to William PE1RAH on his pico transponder. This is enabling-technology for getting transponders aboard the flocks of cubesats. And, it represents a nice contribution toward solving the radio problem the student designers are facing.
While reading Nuts and Volts magazine I came across a pre-packaged OEM VHF/UHF transponder module from a company called Radiometrix. Below are two links for you to find more information about their product lines ...
http://www.radiometrix.com/ http://www.lemosint.com/ (USA rep for Radiometrix)
-- 73 de JoAnne K9JKM k9jkm@amsat.org
Timothy Salo wrote,
I am hopeful that at least some of the work on the MEP will be applicable to the ACP.
I'd like to thank Tim for bringing up the project on AMSAT-BB.
One of the stated intentions of MEP is to continue the digital ground station work that was begun in support of ACP. While MEP is intended to be deployed as a terrestrial system, the model is based off of ACP.
We preserve the idea of a multiple access payload in the "groundsat", which will be a mountaintop repeater instead of in orbit. We are using the same bands, with the only difference being a shift off the satellite sub-bands. We have taken advantage of a greatly improved link budget by orienting the system to high-definition video for terrestrial use.
For satellite use, we would be able to support some number of voice channels, depending on the payload.
We are open invitation and welcome anyone at any level who would like to participate.
Our current phase is exploratory. We're beginning to transition to analyzing requirements, and then we'll design, implement, test and verify. -Michelle W5NYV
Def: MEP = Microwave Experimentation Project
One of the stated intentions of MEP is to continue the digital ground station work that was begun in support of ACP. While MEP is intended to be deployed as a terrestrial system, the model is based off of ACP.
For what it's worth... the issue of high-gain antenna pointing among terrestrial users is being taken care of with an APRS packet that will indicate to everyone on the net, where each person's microwave antenna is pointing live. This can allow for automatic antenna tracking during terrestrial ops. See http://www.aprs.org/info/microwave-exp-proj.txt
We preserve the idea of a multiple access payload in the "groundsat", which will be a mountaintop repeater instead of in orbit. We are using the same bands, with the only difference being a shift off the satellite sub-bands. We have taken advantage of a greatly improved link budget by orienting the system to high-definition video for terrestrial
use.
For satellite use, we would be able to support some number of voice channels, depending on the payload.
We are open invitation and welcome anyone at any level who would like to participate.
Our current phase is exploratory. We're beginning to transition to analyzing requirements, and then we'll design, implement, test and verify. -Michelle W5NYV
C'mon, Drew ... you're only suggesting that because of all the fun you're having on AO-16 :-)
I like this idea a lot, primarily because of AO-16's unique configuration just now. It's great fun to work. Cubesats with this configuration would be great, especially if we could get them together and "on the shelf" as you suggest, ready to go when an unexpected opportunity arises.
Best of all, from my perspective, it gives those of us who enjoy totally portable stations the chance to continue using what in essence amounts to an SSB-capable handheld station (e.g., my FT-817 and Elk antenna, handheld).
Thanks JoAnne for the initial post. And thanks Drew for the great concept.
73 to all,
Tim - N3TL -------------- Original message from "Andrew Glasbrenner" glasbrenner@mindspring.com: --------------
I'll play!
On the drive home from the symposium in Atlanta, I was thinking about a cubesat with a "hybrid" voice repeater. My idea would use a 435 FM uplink because it's easy to generate power enough on the ground, and the Doppler shift moves QRM out of the uplink fast, it's FM and not picky about tuning, and there aren't any illegal telephones that work on the uplink AFAIK. We'd use a 2m SSB downlink, for a few reasons. 2m path loss is less, so given similar antennas we'll get a better downlink. SSB is more efficient than FM, and we also save power by not transmitting unless there is audio on the uplink, a squelch of sorts.
No computer on my satellite either! We'd have some sort of hardware timer that has to be reset every few days to keep the repeater running, so we could meet FCC rules on control. Maybe PL or DTMF?
Wouldn't it be neat to have one of these sitting on the shelf in case a empty spot on a PPOD became available?
73, Drew KO4MA
----- Original Message ----- From: "JoAnne Maenpaa" To: Sent: Monday, November 24, 2008 8:40 PM Subject: [amsat-bb] BBsat Call for ideas
Ok folks,
Its time for some fun ... how about we design and fly our own transponder via the amsat-bb?
I propose BBSat (sounds better than AdHocSat). This is a call for ideas of a single board transponder in cubesat form factor ... what can we put on a 10cm ^2 circuit board? FM, SDR, packet?
Initially there are only two rules ...
- No griping
- This is going to be an open source project
Let us know what you think right here on the -bb ...
-- 73 de JoAnne K9JKM k9jkm@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
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
FM-up and FM-down.
One transmitter on 432. Multiple receivers on 2M -- maybe 8 would be cool each set to a different frequency, each with a distinct PL tone for access.
On the satellite each of the receiver ports is mixed together at audio frequencies and output on the downlink. The volume of the mix is determined by S-meters and the louder signals on the uplink are mixed in at lower volume.. The more power you use, the quieter you sound. This is so while the big guns are chatting away at very quiet, low audio, the guy with the HT has a chance to break in and boom over everyone.
The idea here is to make a satellite where the HT's have a chance. Also, multiple receivers make the system usable over areas where pirates are transmitting on the uplink channel. (Provided pirates aren't on ALL the uplink channels.)
participants (10)
-
Andrew Glasbrenner -
Bruce Robertson -
cathrynham -
Greg D. -
JoAnne Maenpaa -
Michelle -
n3tl＠bellsouth.net -
Robert Bruninga -
Timothy J. Salo -
Tony Langdon