Re: [amsat-bb] going digital
On 07/22/2014 07:27 AM, JoAnne Maenpaa wrote: > When thinking of projects to enter into the digital communication > world plan on building or buying that digital interface to connect > your radio to the soundcard. Soundcard interfaces to existing voice radios were a good start, but it's time to move past them. I've designed several modulation and coding schemes to fit existing radios, and their inherently limited bandwidth is a major pain. For ARISSat-1 I agreed to cram everything through a SSB filter, and I'm not doing that again. Not only does the narrow bandwidth often limit the data rate to much less than what the link budget could actually support, but it enormously aggravates the Doppler problem. It doesn't help that there are no industry-wide standards for SSB phase response or computer tuning, or that every time you retune one (which is often) there is a poorly characterized phase jump. Doppler is much easier to handle at high data rates because it's the ratio of the symbol rate to the Doppler that matters, not the absolute amount of Doppler. Now that we have a variety of "pure digital" radio front ends to choose from, it's time to set aside the voice radio + soundcard model. Not only do the SDRs support wider bandwidths but they tend to be considerably smaller, lighter and easier to work with in software. Some, like the Funcube dongle, are even considerably cheaper than conventional radios. --Phil ___ 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
Re: [amsat-bb] going digital
Ross, You may be wish to watch the presentation to given by Peter Guelzow DB2OS at 11:20 BST (1020 GMT) on Sunday, July 27. Peter will be talking about the equipment required to work the new amateur radio Geostationary 2.4 to 10 GHz payload which may be launched in 2016. Es’HailSat-2 will provide a 250 kHz linear transponder intended for conventional analogue operations in addition to another transponder which will have an 8 MHz bandwidth. The latter transponder is intended for experimental digital modulation schemes and DVB amateur television. http://amsat-uk.org/2014/03/22/geo-transponders-on-eshail-2/ Watch the Colloquium live at http://www.batc.tv/streams/amsat2014 The AMSAT-UK International Space Colloquium is being held on the weekend of July 26-27, 2014 at the Holiday Inn, Guildford, GU2 7XZ, UK. The event is open to all, admittance £10 a day. Further details http://amsat-uk.org/colloquium/colloquium-2014/ Trevor M5AKA AMSAT-UK Website http://amsat-uk.org/ Facebook https://www.facebook.com/amsatuk Twitter https://twitter.com/AMSAT_UK On Thursday, 24 July 2014, 10:09, Ross Whenmouth wrote: Hi, For a digital bird with a 10 GHz downlink, would it make sense to use DVB-S for the downlink? If you did, I think that most specialised part of a ground station would be an appropriate LNB that will mix 10.0 to 10.5 GHz down to IF. Demodulation could then be performed with ordinary consumer grade DVB-S set top boxes and PC based DVB-S interfaces. Out of the box, a consumer DVB-S STB (Set Top Box) can handle both audio channels and video channels. The DVB-S protocol can also multiplex data (PBBS message forwarding? APRS?) along with multiple audio and video channels on the one carrier. The satellite could have multiple uplinks on multiple bands, eg FM voice uplink(s) on 2m, 9k6 data uplink on 70cm, and video/high speed data on shorter wavelengths. So, with say a 2m mobile rig, and a consumer DVB-S setup (with a 10 GHz LNB) you could QSO via the bird. If you want to get into data, video or digital voice, the bird would do that do. 73, ZL2WRW Ross Whenmouth ___ 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
Re: [amsat-bb] going digital
Hi, For a digital bird with a 10 GHz downlink, would it make sense to use DVB-S for the downlink? If you did, I think that most specialised part of a ground station would be an appropriate LNB that will mix 10.0 to 10.5 GHz down to IF. Demodulation could then be performed with ordinary consumer grade DVB-S set top boxes and PC based DVB-S interfaces. Out of the box, a consumer DVB-S STB (Set Top Box) can handle both audio channels and video channels. The DVB-S protocol can also multiplex data (PBBS message forwarding? APRS?) along with multiple audio and video channels on the one carrier. The satellite could have multiple uplinks on multiple bands, eg FM voice uplink(s) on 2m, 9k6 data uplink on 70cm, and video/high speed data on shorter wavelengths. So, with say a 2m mobile rig, and a consumer DVB-S setup (with a 10 GHz LNB) you could QSO via the bird. If you want to get into data, video or digital voice, the bird would do that do. 73, ZL2WRW Ross Whenmouth ___ 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
Re: [amsat-bb] going digital
Circumstances in the launch business have driven many groups, including AMSAT, to select the cubesat path to space. Arguing about an on-going project isn't productive but I find discussions about future possibilities interesting. These discussions don't have come at the expense of the current project plan (such as why use FM when this project is already 2 years in progress). We do have future satellites still on the drawing board however! On the digital radio front Phil makes a very good point ... > So many hams seem to automatically assume, for no good reason, > that getting on any new digital mode must necessarily require > exotic, expensive and hard to find components and a PhD to use. > But the required hardware is now very common, and nearly all > of the "complexity" that defines any particular digital communi- > cation system these days is implemented almost entirely in soft- > ware that costs nothing to copy and distribute once written. I used free software, my FT-857, small yagis at fixed elevation on a TV rotor to decode Delfi, ARISSat, FUNcube, and 2-way with ISS packet. The computer that does this is a bargain e-machine box with the only modification being additional memory. The software tools for digital modes on these satellites were a free download. The key to getting the software and your computer to do this requires one additional piece of hardware if you use an external radio. If you use one of the various flavors of Dongles on your computer you only need to add a software audio path (another download). When thinking of projects to enter into the digital communication world plan on building or buying that digital interface to connect your radio to the soundcard. A few days or weeks spent on the soundcard interface is the key link to enter this exciting other half of satellite operating. There are many paths to soundcard digital interfaces. Google is your friend. I bet a local dealer would love to sell you a RigBlaster (which many have had good luck with). I used a less expensive off-the-shelf digital interface from a place called Donner Digital Interfaces. He sells it on the web: http://www.donnerstore.org/ ... the page is quite an entrepreneur operation, select digital interfaces from the menu on the left side. http://www.youtube.com/watch?v=34dy21z2I8Y ... shows how to set up a Donner interface to your rig. More good news ... the setup for the digital interface is the same for HF, VHF, or UHF. Once installed you have digital modes on all bands. (On HF I use the JT-65 software which often decodes DX signals so weak I cannot hear them by ear - it was just another software download.) PSK and SSTV were more downloads. But ya gotta install that Soundcard interface to get to this good stuff! http://www.eham.net/reviews/detail/2073 ... some reviews and discussion to help your research. -- 73 de JoAnne K9JKM k9...@amsat.org Editor, AMSAT Journal ___ 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
Re: [amsat-bb] going digital
On 07/21/2014 02:53 PM, Paul Stoetzer wrote: > I'm not totally unsympathetic to Phil's ideas. They have quite a bit > of merit, but clearly AMSAT would also have to develop the ground > station equipment in order for it to get a user base that would make > it worthwhile. Absolutely. About 14 years ago (i.e., at the beginning of the 21st century) I made a donation to AMSAT earmarked for the development and initial production of the low-cost ground station hardware absolutely necessary to the success of a new digital satellite mode. I didn't specify any particular digital mode. ANY new satellite mode would qualify as long as it's digital and requires new ground station hardware. As far as I know (the AMSAT treasurer can comment), my donation is still sitting there. > AMSAT's limiting factors are money and volunteer time. Unfortunately, > neither money nor people's time grow on trees. I think you'll find that the supply of both money and volunteer time depends strongly on what that time and money will be used for. If you think the supply is limited, you might consider being a little more imaginative and ambitious in your goals. --Phil ___ 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
Re: [amsat-bb] going digital
On 07/21/2014 02:00 PM, Gus wrote: > Actually, DirecTV is not available for purchase in my neck of the > woods. I can get a system installed, but it wouldn't be my system to > fiddle with. Sorry about that, I was primarily thinking of AMSAT-NA members when I said that. Forget the DirecTV receiver itself and consider their offset-fed Ku-band dishes and 0.7 dB NF LNBs that are readily available on the surplus market. Since DirecTV isn't available in Barbados, paint the dish with the logo of whatever DBS provider you like. Nobody will know the difference. > Phil, I'm not saying it /should/ be, but that if it is, you won't get > many users on the system. So, part of the system design for any such > bird had better include design of low cost, easy to find, simple to use > hardware that will allow me -- or any other doofus like me -- to get QRV > without too much hardship. And here I am with you 100%. So many hams seem to automatically assume, for no good reason, that getting on any new digital mode must necessarily require exotic, expensive and hard to find components and a PhD to use. But the required hardware is now very common, and nearly all of the "complexity" that defines any particular digital communication system these days is implemented almost entirely in software that costs nothing to copy and distribute once written. The hardware to run said software already exists in virtually every ham shack. Even a low-end general purpose PC is a very capable DSP engine, and this has been true for almost 20 years since Intel introduced MMX, their first set of DSP instructions for the x86 CPU. Since then there has been SSE, SSE2, SSE3, SSSE3, SSE4 and now AVX and AVX2, Advanced Vector Extensions 2. Here's an example of how far consumer DSP has come just in the time I've been involved with AMSAT. I wrote the demodulation and decoding software now used by the ISEE-3 Reboot Project. It takes the A/D output of an Ettus USRP software defined radio, tracks the RF carrier, demodulates the phase modulation, tracks and demodulates the binary symbols, and performs error correction to produce raw telemetry frames. ISEE-3 uses a rate 1/2 constraint length k=24 convolutional error correction code. When it was launched in 1978, decoding it took highly specialized, dedicated hardware. Someone here who worked for Linkabit, the manufacturer of that decoding hardware, can probably jump in with the exact cost in millions of dollars and the number of 6' equipment racks it filled. I am doing all these functions on my laptop using not only the Fano algorithm used by that original Linkabit hardware, but also the Viterbi algorithm, which is better at correcting errors in noise. The Viterbi algorithm is traditionally used with much shorter codes (k=7, first used on the Voyagers, is still common) because its complexity doubles each time you increase it by one. Had I suggested, in 1978, using it for a k=24 code (taking 131,072 times as much effort as k=7) NASA would have laughed me out of the room. The same reaction would still have been justified in 1985 when they renamed it ICE and sent it out of earth orbit to the first-ever comet rendezvous, requiring Herculean efforts to overcome the extra path loss. Now I'm doing it all on my 2-year-old Sony laptop. That's how much computing power we hams now have in front of us. All we need is a little imagination and vision as to what it makes possible. Instead there seems to be a contest to see who can produce the most objections, valid or otherwise. Is this what the amateur service (or AMSAT) has become? --Phil ___ 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
Re: [amsat-bb] going digital
On 07/21/2014 06:34 PM, Jim Sanford wrote: Look at what the FunCube guys did! Absolutely. Which is why I said in my initial post on this subject: >> ...any new, digital satellite will have to be developed in parallel with readily available >> ground station modules (Funcube Dongle Deluxe?) that provide the 'average' ham >> a path to participation. Specifically referencing the FCD as an example. The proposal for Phil's 10GHz digital sat would best to include a suitable 10GHz module for ground station use. On 7/21/2014 5:00 PM, Gus wrote: On 07/21/2014 01:00 PM, Phil Karn wrote: > Next questions: > > Does a DirecTV receiving station cost $5K? Actually, DirecTV is not available for purchase in my neck of the woods. I can get a system installed, but it wouldn't be my system to fiddle with. > Are its components hard to source or esoteric? Well, I know where I could nick one, but I'd rather not. Otherwise, I guess I could source one overseas, ship it in, then bow down before the Customs & Excise godlings. ham gear is 10 + 17.5% but there's no way they'd pass that as ham gear, so probably 115 + 17.5% or worse. That might satisfy Rx needs, but wouldn't include a transmitter Does that sound hard to source or esoteric? > If not, what makes you think that a digital ground station for an AMSAT satellite should be? Phil, I'm not saying it /should/ be, but that if it is, you won't get many users on the system. So, part of the system design for any such bird had better include design of low cost, easy to find, simple to use hardware that will allow me -- or any other doofus like me -- to get QRV without too much hardship. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ___ 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 -- Gus 8P6SM The Easternmost Isle ___ 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
Re: [amsat-bb] going digital
Look at what the FunCube guys did! On 7/21/2014 5:00 PM, Gus wrote: On 07/21/2014 01:00 PM, Phil Karn wrote: > Next questions: > > Does a DirecTV receiving station cost $5K? Actually, DirecTV is not available for purchase in my neck of the woods. I can get a system installed, but it wouldn't be my system to fiddle with. > Are its components hard to source or esoteric? Well, I know where I could nick one, but I'd rather not. Otherwise, I guess I could source one overseas, ship it in, then bow down before the Customs & Excise godlings. ham gear is 10 + 17.5% but there's no way they'd pass that as ham gear, so probably 115 + 17.5% or worse. That might satisfy Rx needs, but wouldn't include a transmitter Does that sound hard to source or esoteric? > If not, what makes you think that a digital ground station for an AMSAT satellite should be? Phil, I'm not saying it /should/ be, but that if it is, you won't get many users on the system. So, part of the system design for any such bird had better include design of low cost, easy to find, simple to use hardware that will allow me -- or any other doofus like me -- to get QRV without too much hardship. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ___ 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
Re: [amsat-bb] going digital
Which is exactly what the FunCube guys did, and look at what they've wrought!! 73, Jim wb4...@amsat.org When DirecTV designed their satellite broadcast system, did they worry about backward compatibility with the multitude (or so it probably seemed) of existing C-band BUD (Big Ugly Dish) owners? All of whom were then receiving analog FM, I might add. If not, then why are they still in business? Probably because they didn't design a satellite. They designed an entire _/*system*/_ including ground station components as well as flight hardware. The ground system components were made available such that their target audience was able to upgrade their BUD installations with only reasonable expenditures of time, effort and money. But that's just a guess in my part. I'd love to chat with you on the new digital hamsat, but if it's going to require I spend $5k+ on hard-to-source, esoteric components and cobble them together with duct tape, then it'll be a while before I'm QRV. So, the first few days after launch those 60 DV channels may be a little quiet. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ___ 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
Re: [amsat-bb] going digital
I'm not totally unsympathetic to Phil's ideas. They have quite a bit of merit, but clearly AMSAT would also have to develop the ground station equipment in order for it to get a user base that would make it worthwhile. I know this was planned for Eagle, but that was for a HEO which would have many hours a day of visibility for everyone. It's difficult to rationalize spending money on equipment good for a single LEO satellite at this point, especially one that would be as complex as is contemplated here. I am intrigued by digital operations. My current operating situation prevents me from doing much in that field (I have to carry the radios and hold the antenna, no more hands for a computer). I followed the unsuccessful FreeDV via FO-29 trials between W0DHB and NX9G last year. When the DSTAR parrot repeater that was recently launched is activated, I will certainly borrow a DSTAR radio to try it out. Maybe I'll even buy one! AMSAT's limiting factors are money and volunteer time. Unfortunately, neither money nor people's time grow on trees. I do think that multiple launches by AMSAT-NA will lead to a resurgence of interest in North America, especially when people realize just how easy Fox is going to be to hear. The launches are also going to occur at a time when solar activity is falling, those with limited antenna situations might look to other aspects of amateur radio while conditions on the higher HF bands are poor. Hopefully those factors will help to provide the resources for more complex projects! 73, Paul, N8HM On Mon, Jul 21, 2014 at 5:00 PM, Gus wrote: > On 07/21/2014 01:00 PM, Phil Karn wrote: > > > Next questions: > > > > Does a DirecTV receiving station cost $5K? > > Actually, DirecTV is not available for purchase in my neck of the woods. I > can get a system installed, but it wouldn't be my system to fiddle with. > > > > Are its components hard to source or esoteric? > > Well, I know where I could nick one, but I'd rather not. Otherwise, I guess > I could source one overseas, ship it in, then bow down before the Customs & > Excise godlings. ham gear is 10 + 17.5% but there's no way they'd pass > that as ham gear, so probably 115 + 17.5% or worse. That might satisfy Rx > needs, but wouldn't include a transmitter Does that sound hard to > source or esoteric? > > > > If not, what makes you think that a digital ground station for an AMSAT > satellite should be? > > Phil, I'm not saying it /should/ be, but that if it is, you won't get many > users on the system. So, part of the system design for any such bird had > better include design of low cost, easy to find, simple to use hardware that > will allow me -- or any other doofus like me -- to get QRV without too much > hardship. > > > -- > Gus 8P6SM > The Easternmost Isle > > ___ > 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
Re: [amsat-bb] going digital
On 07/21/2014 01:00 PM, Phil Karn wrote: > Next questions: > > Does a DirecTV receiving station cost $5K? Actually, DirecTV is not available for purchase in my neck of the woods. I can get a system installed, but it wouldn't be my system to fiddle with. > Are its components hard to source or esoteric? Well, I know where I could nick one, but I'd rather not. Otherwise, I guess I could source one overseas, ship it in, then bow down before the Customs & Excise godlings. ham gear is 10 + 17.5% but there's no way they'd pass that as ham gear, so probably 115 + 17.5% or worse. That might satisfy Rx needs, but wouldn't include a transmitter Does that sound hard to source or esoteric? > If not, what makes you think that a digital ground station for an AMSAT satellite should be? Phil, I'm not saying it /should/ be, but that if it is, you won't get many users on the system. So, part of the system design for any such bird had better include design of low cost, easy to find, simple to use hardware that will allow me -- or any other doofus like me -- to get QRV without too much hardship. -- Gus 8P6SM The Easternmost Isle ___ 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
Re: [amsat-bb] going digital
On 07/21/2014 06:00 AM, Gus wrote: > Probably because they didn't design a satellite. They designed an > entire system including ground station components as well as flight > hardware. The ground system components were made available such that > their target audience was able to upgrade their BUD installations with > only reasonable expenditures of time, effort and money. But that's just > a guess in my part. Bingo! > I'd love to chat with you on the new digital hamsat, but if it's going > to require I spend $5k+ on hard-to-source, esoteric components and > cobble them together with duct tape, then it'll be a while before I'm > QRV. So, the first few days after launch those 60 DV channels may be a > little quiet. Next questions: Does a DirecTV receiving station cost $5K? Are its components hard to source or esoteric? If not, what makes you think that a digital ground station for an AMSAT satellite should be? --Phil ___ 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
Re: [amsat-bb] going digital
Since I think it so apropos to our discussion of old vs new technology in AMSAT, I hereby quote in full today's "Borowitz Report" from the New Yorker. Rarely does an item cause me to laugh and feel pain at the same time, but this is one of those cases. --Phil [Picture of Buzz Aldrin saluting the flag on the moon during Apollo 11] MINNEAPOLIS (The Borowitz Report)—Historians studying archival photographs from four decades ago have come to the conclusion that the U.S. must have believed in science at some point. According to the historian Davis Logsdon, who has been sifting through mounds of photographic evidence at the University of Minnesota, the nation apparently once held the view that investing in science and even math could yield accomplishments that would be a source of national pride. While Logsdon has not developed a complete theory to explain the United States’ pro-science stance during that era, he attributes some of it to the liberal views of the President at that time, Richard M. Nixon. Source: http://www.newyorker.com/humor/borowitz-report/nation-apparently-believed-science-point ___ 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
Re: [amsat-bb] going digital
On 07/21/2014 01:57 AM, Phil Karn wrote: On 07/20/2014 08:00 PM, Gus wrote: I'd hazard to guess that the 'average' shack has multi-mode HF capability, along with VHF/UHF FM. Some lesser number of 'average' shacks will have multi-mode VHF/UHF, or could readily acquire that capability without too much expenditure in resources (time, effort, money). When DirecTV designed their satellite broadcast system, did they worry about backward compatibility with the multitude (or so it probably seemed) of existing C-band BUD (Big Ugly Dish) owners? All of whom were then receiving analog FM, I might add. If not, then why are they still in business? Probably because they didn't design a satellite. They designed an entire system including ground station components as well as flight hardware. The ground system components were made available such that their target audience was able to upgrade their BUD installations with only reasonable expenditures of time, effort and money. But that's just a guess in my part. I'd love to chat with you on the new digital hamsat, but if it's going to require I spend $5k+ on hard-to-source, esoteric components and cobble them together with duct tape, then it'll be a while before I'm QRV. So, the first few days after launch those 60 DV channels may be a little quiet. -- Gus 8P6SM The Easternmost Isle ___ 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
Re: [amsat-bb] going digital
On 07/20/2014 08:00 PM, Gus wrote: > I'd hazard to guess that the 'average' shack has multi-mode HF > capability, along with VHF/UHF FM. Some lesser number of 'average' > shacks will have multi-mode VHF/UHF, or could readily acquire that > capability without too much expenditure in resources (time, effort, money). When DirecTV designed their satellite broadcast system, did they worry about backward compatibility with the multitude (or so it probably seemed) of existing C-band BUD (Big Ugly Dish) owners? All of whom were then receiving analog FM, I might add. If not, then why are they still in business? --Phil ___ 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
Re: [amsat-bb] going digital
On 07/20/2014 06:13 AM, Simon Brown wrote: > John, > > If both side have good Doppler correction then it can be done, but you have > to choose the correct mode as there are other issues even if the Doppler > correction is perfect, especially when the range is changing at its maximum, > for example as the satellite passes overhead. Correct, but Doppler actually gets much easier to deal with as the data rate increases. What matters is the *ratio* of the Doppler to the data rate (actually the channel symbol rate, which is usually higher). At the very high rates possible from LEO on the microwave bands, Doppler on a BPSK signal can be easily tracked by a Costas loop even without orbit prediction steering (though it's still a good idea). E.g., a relative velocity of 3 km/s at 10 GHz is a Doppler of 100 kHz, considerably less than the symbol rates possible from LEO with even small transmitter powers and antenna gains. Compare this with the numbers for current amateur satellites on VHF and UHF. --Phil ___ 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
Re: [amsat-bb] going digital
I'm all in favour of new modes and new technology. Pushing the boundaries should be a primary goal. But before any new bird is put in the sky, surely the target audience must be considered? I'd hazard to guess that the 'average' shack has multi-mode HF capability, along with VHF/UHF FM. Some lesser number of 'average' shacks will have multi-mode VHF/UHF, or could readily acquire that capability without too much expenditure in resources (time, effort, money). Accept that we want to launch boundary-expanding, technologically advanced satellites if possible. What sort of equipment should we expect to find in the shacks of those hams who are the target audience for these new satellites? How big is this suitably equipped target audience? Big enough to justify having their own satellite? How much time, effort and money will it take to upgrade an 'average' shack (like mine) to meet the requirements of being a part of the target audience? I'm really pro- and not anti- here. But it may be that any new, digital satellite will have to be developed in parallel with readily available ground station modules (Funcube Dongle Deluxe?) that provide the 'average' ham a path to participation. Again: Interested to hear roughly what capabilities would be needed to join the gang working the new digital birds, when they fly. -- Gus 8P6SM The Easternmost Isle ___ 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
Re: [amsat-bb] going digital
On 07/20/2014 03:45 AM, John / NS1Z wrote: > Is there some reason why a digital signal cannot be passed thru an > analog/linear transponder? What goes in is what comes out. I forgot to mention that a FM repeater is not a linear transponder. Although FM is constant envelope and a FM RF power amplifier can therefore be made pretty efficient, it will not support a power-efficient modulation mode like coherent BPSK. Single channel FM is about the worst possible choice for a multiple access satellite uplink. Not only is it analog and noncoherent, but because it's noncoherent it has a capture effect. For a signal to come through at all, it must capture the channel over all noise and interference. This also severely limits the power improvement that can be attained with forward error correction; if the demodulator is below threshold, coding can't help you. Depending on the demodulator design the capture ratio is somewhere around 10 dB or slightly less, which means that the capturing signal must be at least 10 times as strong as *all* of the interferers combined. This makes it more or less useless unless there's only one user (in which case it's no longer multiple access) or the users are highly disciplined (which is hardly the case in the amateur service). --Phil ___ 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
Re: [amsat-bb] going digital
On 07/20/2014 03:45 AM, John / NS1Z wrote: > Is there some reason why a digital signal cannot be passed thru an > analog/linear transponder? What goes in is what comes out. It seems the > lack of transponder bandwidth limits the digital signal experimenter... > Maybe that is why commercial transponders on satellites are linear. They > can take any modulation and retransmit it : AM, FM, PM or CB You certainly can, and as you point out there are a lot of commercial satellite transponders that do just that. But the most common practice there is to drive the transponder power amplifier into nonlinear saturation to increase its efficiency, and that limits you to a single signal at a time. Some transponders are shared among multiple simultaneous ground transmitters, and to avoid intermodulation distortion they have to back off on their uplink powers to keep the transponder linear. So besides having to divide the transponder power by N users, the transponder converts DC to RF much less efficiently. Linear power amplifiers are inherently much less efficient than nonlinear (constant envelope) amplifiers. AMSAT (specifically AMSAT-DL) has done quite a bit of work to increase linear amplifier efficiency, but the techniques tend to be inherently limited in bandwidth (a few hundred kHz max). Much wider bandwidths are available at microwave, and since the link budgets in LEO support them we'd like to use them. The transponder also repeats a certain amount of uplink noise, though in LEO it isn't hard to saturate the uplink receiver so this isn't much of a factor. But again you tend to be limited to a single user at a time. So there are considerable advantages to making the satellite itself digital. It can emit a digital modulation designed to be maximally power efficient, and it can do so continuously and at full power (solar panels and batteries permitting). This makes it easy to acquire and track at the ground station. Spacecraft power efficiency is our prime consideration, as it determines the size and cost of the satellite and the required size of the ground station antenna. And we're trying to minimize that to make our satellite appeal to many more hams. Multiuser satellite uplinks and downlinks are fundamentally different problems, and in a digital satellite with onboard processing the uplink can easily use a different modulation optimized for the problem. There are several good options: FDMA as in the PACSATs, CDMA (spread spectrum), and TDMA. You can even use more than one in combination, e.g., FDMA or TDMA for the continuous high volume users and CDMA for the intermittent low volume users. The user data streams can be easily multiplexed onto the single downlink stream along with data generated within the satellite itself, such as telemetry, camera images and scientific instruments, or stored for later transmission over a different part of the earth. --Phil ___ 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
Re: [amsat-bb] going digital
John, If both side have good Doppler correction then it can be done, but you have to choose the correct mode as there are other issues even if the Doppler correction is perfect, especially when the range is changing at its maximum, for example as the satellite passes overhead. Simon Brown G4ELI http://v2.sdr-radio.com -Original Message- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of John / NS1Z Sent: 20 July 2014 11:46 To: Phil Karn; Paul Stoetzer Cc: amsat-bb@amsat.org Subject: Re: [amsat-bb] going digital Is there some reason why a digital signal cannot be passed thru an analog/linear transponder? What goes in is what comes out. It seems the lack of transponder bandwidth limits the digital signal experimenter... Maybe that is why commercial transponders on satellites are linear. They can take any modulation and retransmit it : AM, FM, PM or CB The biggest problem would be the taxi-cabs etc -Original Message- From: Phil Karn Sent: Saturday, July 19, 2014 4:24 PM To: Paul Stoetzer Cc: amsat-bb@amsat.org Subject: Re: [amsat-bb] ANS-199 AMSAT News Service Special Bulletin - AMSAT Fox-1C Launch Opportunity Announced On 07/19/2014 12:28 PM, Paul Stoetzer wrote: > Are FM repeater satellites what we all want in orbit? No. Personally, > I'd like a Mode J linear transponder in a sun synchronous circular > orbit of about 2,000km (if we can't get anything to HEO). Getting a launch opportunity is difficult and expensive. Going digital is not. ___ 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
Re: [amsat-bb] going digital
Is there some reason why a digital signal cannot be passed thru an analog/linear transponder? What goes in is what comes out. It seems the lack of transponder bandwidth limits the digital signal experimenter... Maybe that is why commercial transponders on satellites are linear. They can take any modulation and retransmit it : AM, FM, PM or CB The biggest problem would be the taxi-cabs etc -Original Message- From: Phil Karn Sent: Saturday, July 19, 2014 4:24 PM To: Paul Stoetzer Cc: amsat-bb@amsat.org Subject: Re: [amsat-bb] ANS-199 AMSAT News Service Special Bulletin - AMSAT Fox-1C Launch Opportunity Announced On 07/19/2014 12:28 PM, Paul Stoetzer wrote: Are FM repeater satellites what we all want in orbit? No. Personally, I'd like a Mode J linear transponder in a sun synchronous circular orbit of about 2,000km (if we can't get anything to HEO). Getting a launch opportunity is difficult and expensive. Going digital is not. ___ 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
