Hi All,
We are looking for a practical system to use on a 1U, or perhaps 2U, cubesat to take medium definition images and transmit them to the ground on VHF for educational outreach purposes.
All the usual cubesat mass, power, data budgets would apply but and I would especially appreciate advice and guidance about the best type of digital slow scan (or similar) system to adopt.
I am aware of the SSDV system used on some balloon flights http://ukhas.org.uk/guides:ssdv
Thanks in advance for all comments ideas and observations and especially any offers of support!
73
Graham G3VZV
Graham,
What's 'medium resolution' ? Standard SSTV is not digital, it's analogous with the (now no longer used) analogue TV. There is true digital SSTV used on 80m and 40m and (I guess) other bands, from memory this is EasyPal; to implement this in a satellite would be a long and tedious task.
Implementing one of the analogue SSTV modes would be easier - much easier - but quality is nowhere as good.
Simon Brown, HB9DRV http://sdr-radio.com
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Graham Shirville
We are looking for a practical system to use on a 1U, or perhaps 2U, cubesat to take medium definition images and transmit them to the ground on VHF for educational outreach purposes.
Hi Simon,
Good question - "medium" was a deliberately vague term as it will also depend on the camera and available data rates etc.
I was hoping we might be able to move on from analogue SSTV now.. we should be able to achieve much better quality images,,,as you suggest the challenge would be to do the digital encoding on board the spacecraft without using lots of power but, as mentioned, - if they can do it on a tiny payload hanging beneath a small helium balloon then it should be possible to do something similar on a spacecraft even a 1U cubesat!
73
Graham G3VZV
-----Original Message----- From: Simon HB9DRV Sent: Friday, September 07, 2012 2:13 PM To: 'Graham Shirville' ; 'AMSAT BB' Subject: [amsat-bb] Re: Fw: Digital Slow Scan in space
Graham,
What's 'medium resolution' ? Standard SSTV is not digital, it's analogous with the (now no longer used) analogue TV. There is true digital SSTV used on 80m and 40m and (I guess) other bands, from memory this is EasyPal; to implement this in a satellite would be a long and tedious task.
Implementing one of the analogue SSTV modes would be easier - much easier - but quality is nowhere as good.
Simon Brown, HB9DRV http://sdr-radio.com
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Graham Shirville
We are looking for a practical system to use on a 1U, or perhaps 2U, cubesat to take medium definition images and transmit them to the ground on VHF for educational outreach purposes.
_______________________________________________ Sent via [email protected]. 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
Well you should be able to do it on small ARM processor, but you've always got to take transmission time into account - those pesky satellites do tend to move about quite a bit :)
There's also the format used by the NOAA weather satellites - simple and works...
Simon Brown, HB9DRV http://sdr-radio.com
-----Original Message----- From: Graham Shirville [mailto:[email protected]]
Good question - "medium" was a deliberately vague term as it will also depend on the camera and available data rates etc.
I was hoping we might be able to move on from analogue SSTV now.. we should be able to achieve much better quality images,,,as you suggest the challenge would be to do the digital encoding on board the spacecraft without using lots of power but, as mentioned, - if they can do it on a tiny payload hanging beneath a small helium balloon then it should be possible to do something similar on a spacecraft even a 1U cubesat!
Hi both.
I believe the digital SSTV that is used on HF / VHF is in reality DRM, which is a forward error corrected digital communications standard (?) I suppose the real difficulty is implementing a method of reading an image file and then encoding it for transmission in a broadcast type format for general reception rather than one that requires handshaking or acknowledgments from the groundstation.
An essential feature would be that whenever a 'packet' of data is received, that data is displayed rather than waiting for the complete image to be received error free. I couldn't find much on DRM encoding but I think it was originally intended for digital voice in a narrow bandwidth so it sounds suitable for low power satellite use.
Thanks
David
-----Original Message----- From: Simon HB9DRV [email protected] To: 'Graham Shirville' [email protected]; 'AMSAT BB' [email protected] Sent: Fri, 7 Sep 2012 21:51 Subject: [amsat-bb] Re: Fw: Digital Slow Scan in space
Well you should be able to do it on small ARM processor, but you've always got to take transmission time into account - those pesky satellites do tend to move about quite a bit :)
There's also the format used by the NOAA weather satellites - simple and works...
Simon Brown, HB9DRV http://sdr-radio.com
-----Original Message----- From: Graham Shirville [mailto:[email protected]]
Good question - "medium" was a deliberately vague term as it will also depend on the camera and available data rates etc.
I was hoping we might be able to move on from analogue SSTV now.. we should be able to achieve much better quality images,,,as you suggest the challenge would be to do the digital encoding on board the spacecraft without using lots of power but, as mentioned, - if they can do it on a tiny payload hanging beneath a small helium balloon then it should be possible to do something similar on a spacecraft even a 1U cubesat!
_______________________________________________ Sent via [email protected]. 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
--- On Fri, 7/9/12, [email protected] [email protected] wrote:
An essential feature would be that whenever a 'packet' of data is received, that data is displayed rather than waiting for the complete image to be received error free. I couldn't find much on DRM encoding but I think it was originally intended for digital voice in a narrow bandwidth so it sounds suitable for low power satellite use.
WinDRM (and DRMDV/FDMDV) were written by Cesco Lanza HB9TLK some info at http://n1su.com/windrm/download.html
To achieve a reasonable data rate it's usually run at 64QAM (with full SSB bandwidth). 64 QAM is less robust and requires a higher S/N.
I've no idea what the practical effects of a high Doppler shift would be, although a computerized station with frequent Doppler correction should track it okay.
Is the data rate on High Altitude Balloons about 300 bps ? I've never received any images from them but if 300 bps is correct then the images are either low res or take a long time to send ?
Analog SSTV is still going strong some 6 years after the introduction of Digital SSTV perhaps indicating that existing Digital SSTV approaches do not yet match the performance/robustness/ease of use of analog for HF working.
73 Trevor M5AKA
Hi All,
SSDV indeed shows you the images "as they come in" Most High Altitude Balloons use RTTY with relatively slow baudrates. The balloons are limited to using FSK modems in the ISM bands, because of legal issues. Therefore, RTTY is the most feasable mode. Tim Zaman here in the Netherlands has run 1200bd RTTY before on a balloon. see http://www.timzaman.com/?page_id=1106&lang=en He used the faster baudrate to send bigger pictures in the same time and was running two baudrates alternating.
For satellites, you could run a more complex downlink off course, with less transmission time and FEC. 64QAM might work on bigger sats, but I think it is not feasible for a one or 2u satellite at the moment. I would place my bet on flying BPSK/QPSK for now, and more complex things later.
Needless to say that I agree with David about the handshaking and ACKs, but the balloons don't do that either. I do not know anything on HF SSTV, but I have seen SSDV working just fine.
Wouter PA3WEG
On Sat, Sep 8, 2012 at 9:54 AM, Trevor . [email protected] wrote:
--- On Fri, 7/9/12, [email protected] [email protected] wrote:
An essential feature would be that whenever a 'packet' of data is received, that data is displayed rather than waiting for the complete image to be received error free. I couldn't find much on DRM encoding but I think it was originally intended for digital voice in a narrow bandwidth so it sounds suitable for low power satellite use.
WinDRM (and DRMDV/FDMDV) were written by Cesco Lanza HB9TLK some info at http://n1su.com/windrm/download.html
To achieve a reasonable data rate it's usually run at 64QAM (with full SSB bandwidth). 64 QAM is less robust and requires a higher S/N.
I've no idea what the practical effects of a high Doppler shift would be, although a computerized station with frequent Doppler correction should track it okay.
Is the data rate on High Altitude Balloons about 300 bps ? I've never received any images from them but if 300 bps is correct then the images are either low res or take a long time to send ?
Analog SSTV is still going strong some 6 years after the introduction of Digital SSTV perhaps indicating that existing Digital SSTV approaches do not yet match the performance/robustness/ease of use of analog for HF working.
73 Trevor M5AKA
Sent via [email protected]. 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
Argent Data makes a small SSTV camera about 1.5" cube for under $100. For all practical purposes it is a modern replacement for the original Kenwood VC-H1 SSTV handheld. He makes them for balloons etc.
We have one on a model satellite hanging out in our lobby and anyone can trigger it with any FRS radio with the right channel and tone, and then they can also receive and display the picture on any laptop with SSTV software on it by just letting the laptop's mic hear the FRS radio speaker.
The intent of this "spysat" in the lobby was so we could see when someone was having a reception out there and there might be free food.
Bob, WB4APR
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Graham Shirville Sent: Friday, September 07, 2012 4:39 PM To: Simon HB9DRV; 'AMSAT BB' Subject: [amsat-bb] Re: Fw: Digital Slow Scan in space
Hi Simon,
Good question - "medium" was a deliberately vague term as it will also depend on the camera and available data rates etc.
I was hoping we might be able to move on from analogue SSTV now.. we should be able to achieve much better quality images,,,as you suggest the challenge would be to do the digital encoding on board the spacecraft without using lots of power but, as mentioned, - if they can do it on a tiny payload hanging beneath a small helium balloon then it should be possible to do something similar on a spacecraft even a 1U cubesat!
73
Graham G3VZV
-----Original Message----- From: Simon HB9DRV Sent: Friday, September 07, 2012 2:13 PM To: 'Graham Shirville' ; 'AMSAT BB' Subject: [amsat-bb] Re: Fw: Digital Slow Scan in space
Graham,
What's 'medium resolution' ? Standard SSTV is not digital, it's analogous with the (now no longer used) analogue TV. There is true digital SSTV used on 80m and 40m and (I guess) other bands, from memory this is EasyPal; to implement this in a satellite would be a long and tedious task.
Implementing one of the analogue SSTV modes would be easier - much easier - but quality is nowhere as good.
Simon Brown, HB9DRV http://sdr-radio.com
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Graham Shirville
We are looking for a practical system to use on a 1U, or perhaps 2U, cubesat to take medium definition images and transmit them to the ground on VHF for educational outreach purposes.
_______________________________________________ Sent via [email protected]. 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 [email protected]. 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
participants (7)
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g0mrf＠aol.com -
Graham Shirville -
Graham Shirville -
Robert Bruninga -
Simon HB9DRV -
Trevor . -
Wouter Weggelaar