Re: [time-nuts] Airraft Ping Timing
On Tue, Mar 25, 2014 at 6:22 PM, Joe Leikhim wrote: > One thing I don't fully understand are the spot beams. If this is a bent > pipe, how do they control which beam serves the terminal? And if ground > based command, would they not have a record of which spot beam that MH370 > was utilizing, therefore know approximate location and direction ? The spot beams are only used for high speed data, like for example a phone call. The data rate for status reporting is very low, Only a few hundred baud if I remember right. I think they have to request a spot beam connection via the low speed link to get one. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
Hi Joe: It's my understanding that the spot beams are only used for air phones where they need more gain and MH370 had no first class, i.e. no phones. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Joe Leikhim wrote: One thing I don't fully understand are the spot beams. If this is a bent pipe, how do they control which beam serves the terminal? And if ground based command, would they not have a record of which spot beam that MH370 was utilizing, therefore know approximate location and direction ? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
One thing I don't fully understand are the spot beams. If this is a bent pipe, how do they control which beam serves the terminal? And if ground based command, would they not have a record of which spot beam that MH370 was utilizing, therefore know approximate location and direction ? -- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida jleik...@leikhim.com 407-982-0446 WWW.LEIKHIM.COM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
Certainly, if it's a bent-pipe repeater, that makes extracting the Dopplar a whole lot easier. Furthermore, since it's unlikely that the missing plane was the only signal, you can essentially do a differential Dopplar measurement against other sorces, stationary or moving in a know trajectory. -John == > On Mon, Mar 24, 2014 at 06:15:57PM -0700, Chris Albertson wrote: >> Yes, word is that they were able to determine the Doppler shift in the >> plane's signal. I'm surprised this was even recorded but it must have >> been >> in the satellite's telemetry downlink. Projecting radial velocity and >> constraining it to be close to the earth's surface, I guess determines >> one >> path and the direction on it. > > > Perhaps some of the readers here are unaware that the INMARSAT > F3 in question is a bent pipe repeater in both directions. It takes a > C band uplink from the ground and turns it around to L band, and turns L > band uplinks around to a C band downlink. > > It has 8 spot beams, and one regional beam. Channelization of > the uplink and downlink bandwidth and an board switch matrix allows > various allocations of frequencies and bandwidth to the 9 beams varying > with load and demand. > > There is no on satellite signal demodulation/modulation or > protocol processing for the classic AERO signals to/from the plane ... > that is ALL done on ground at the GES (in Perth Australia AFAIK). > > This would make it possible for INMARSAT (and others in the > region tasked with monitoring such things) to capture the actual > repeated RF from the plane and digitize it - this happens in the ground > equipment as part of the normal processing anyway - and dumping it to a > disk array somewhere is certain to be going on, either both inside > INMARSAT at the GES or at least at other (less public) sites such as > Alice Springs. The C band downlinks are global beams BTW and can > be received anywhere that sees the satellite. > > As such the quality of the recovered Doppler and other signal > parameters is very much a function of the stability of the various LOs > (and sample clocks) involved, which I believe can correctly be presumed > to be really high grade both in space and certainly on the ground. AES > (plane) timing and frequency may be less good, but it is more or less > locked to the L band downlink timing and frequency signals as reference. > > The newer INMARSAT F4 birds do have DSP processing on the > satellite, but apparently NOT used for demodulating and processing the > various control channel signals on the satellite - but just for doing > beam forming and power allocation for the 120 spot beams these birds > support. This of course would impact delay through the satellite > for precision timing and ranging. > > But so far there are no reports that the F4 POR satellite was > involved. The high gain antennas on the AES (plane) are fairly > directional and if they were in use there might not be a lot of signal > seen on the POR bird. Not sure if those pings would have been sent > via a low gain antenna on the AES, but I suspect normally not. > > -- > Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass > 02493 > "An empty zombie mind with a forlorn barely readable weatherbeaten > 'For Rent' sign still vainly flapping outside on the weed encrusted pole - > in > celebration of what could have been, but wasn't and is not to be now > either." > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
On Mon, Mar 24, 2014 at 06:15:57PM -0700, Chris Albertson wrote: > Yes, word is that they were able to determine the Doppler shift in the > plane's signal. I'm surprised this was even recorded but it must have been > in the satellite's telemetry downlink. Projecting radial velocity and > constraining it to be close to the earth's surface, I guess determines one > path and the direction on it. Perhaps some of the readers here are unaware that the INMARSAT F3 in question is a bent pipe repeater in both directions. It takes a C band uplink from the ground and turns it around to L band, and turns L band uplinks around to a C band downlink. It has 8 spot beams, and one regional beam. Channelization of the uplink and downlink bandwidth and an board switch matrix allows various allocations of frequencies and bandwidth to the 9 beams varying with load and demand. There is no on satellite signal demodulation/modulation or protocol processing for the classic AERO signals to/from the plane ... that is ALL done on ground at the GES (in Perth Australia AFAIK). This would make it possible for INMARSAT (and others in the region tasked with monitoring such things) to capture the actual repeated RF from the plane and digitize it - this happens in the ground equipment as part of the normal processing anyway - and dumping it to a disk array somewhere is certain to be going on, either both inside INMARSAT at the GES or at least at other (less public) sites such as Alice Springs. The C band downlinks are global beams BTW and can be received anywhere that sees the satellite. As such the quality of the recovered Doppler and other signal parameters is very much a function of the stability of the various LOs (and sample clocks) involved, which I believe can correctly be presumed to be really high grade both in space and certainly on the ground. AES (plane) timing and frequency may be less good, but it is more or less locked to the L band downlink timing and frequency signals as reference. The newer INMARSAT F4 birds do have DSP processing on the satellite, but apparently NOT used for demodulating and processing the various control channel signals on the satellite - but just for doing beam forming and power allocation for the 120 spot beams these birds support. This of course would impact delay through the satellite for precision timing and ranging. But so far there are no reports that the F4 POR satellite was involved. The high gain antennas on the AES (plane) are fairly directional and if they were in use there might not be a lot of signal seen on the POR bird. Not sure if those pings would have been sent via a low gain antenna on the AES, but I suspect normally not. -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 "An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either." ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
On 3/25/14 11:38 AM, J. Forster wrote: Could well be. I never saw the bird, of course. The portable ground station was roughly the same size as an OD Manpak radio of the period and read out Lat/Long on LED digital readouts. In retrospect, it may have been in the early 1980s. Transit, transmitted signals at 400 MHz. Had really high performance Quartz oscillators on board (in a dewar, etc.) made by APL. those oscillators became the basis of the Ultrastable oscillators we use in space now. From an oscillator standpoint, not a whole lot different than back then. There's a whole lot of attention paid to how the crystal is mounted, what the aging characteristic is, etc. USO manufacture is definitely a way to be paid to be a time-nut, because that's what it's really about. Finding all the possible ways that might degrade it and driving them all as small as possible. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
On 3/24/14 10:18 PM, David McGaw wrote: I am surprised it took them this long. A number of satellite telemetry systems can use doppler as a matter of course for locating transmitters, such as Iridium and Argos. Those are actually designed for measuring Doppler.. That's really the difference.. This was probably figured out after the fact in an ad hoc way. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
Could well be. I never saw the bird, of course. The portable ground station was roughly the same size as an OD Manpak radio of the period and read out Lat/Long on LED digital readouts. In retrospect, it may have been in the early 1980s. -John == > Hi, > >> Yes, and there was an early military positioning system, roughly 1960s / >> 1970s that worked on Dopplar also. The name escapes me at the moment. > > I think it is Transit. > See http://en.wikipedia.org/wiki/Transit_(satellite) > > Greetings, > Pieter. > >> >> -John >> >> = >> >> >> >>> This is how ELT locating satellites work (when not relaying the newer >>> GPS >>> data bursts). Several on another list I watch suggested this pretty >>> early >>> on and I guess INMARSAT got the message. I'd be curious to know if >>> AFRCC >>> pointed INMARSAT in that direction. >>> >>> Really shows the value of precise and stable time references! >>> >>> >>> >>> >>> Date: Mon, 24 Mar 2014 16:06:14 -0700 (PDT) >>> From: "J. Forster" >>> To:time-nuts@febo.com >>> Subject: [time-nuts] Airraft Ping Timing >>> Message-ID: >>> <13855.12.226.214.5.1395702374.squir...@popaccts.quikus.com> >>> Content-Type: text/plain;charset=iso-8859-1 >>> >>> According to a report on FOX, INMARSAT was able to determine the >>> Malasia >>> Air followed the southern traectory from the Dopplar of the pings. They >>> verified their model by tracking other planes. >>> >>> -John >>> >>> = >>> >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
Hi, > Yes, and there was an early military positioning system, roughly 1960s / > 1970s that worked on Dopplar also. The name escapes me at the moment. I think it is Transit. See http://en.wikipedia.org/wiki/Transit_(satellite) Greetings, Pieter. > > -John > > = > > > >> This is how ELT locating satellites work (when not relaying the newer >> GPS >> data bursts). Several on another list I watch suggested this pretty >> early >> on and I guess INMARSAT got the message. I'd be curious to know if >> AFRCC >> pointed INMARSAT in that direction. >> >> Really shows the value of precise and stable time references! >> >> >> >> >> Date: Mon, 24 Mar 2014 16:06:14 -0700 (PDT) >> From: "J. Forster" >> To:time-nuts@febo.com >> Subject: [time-nuts] Airraft Ping Timing >> Message-ID: >> <13855.12.226.214.5.1395702374.squir...@popaccts.quikus.com> >> Content-Type: text/plain;charset=iso-8859-1 >> >> According to a report on FOX, INMARSAT was able to determine the Malasia >> Air followed the southern traectory from the Dopplar of the pings. They >> verified their model by tracking other planes. >> >> -John >> >> = >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
Yes, and there was an early military positioning system, roughly 1960s / 1970s that worked on Dopplar also. The name escapes me at the moment. -John = > This is how ELT locating satellites work (when not relaying the newer GPS > data bursts). Several on another list I watch suggested this pretty early > on and I guess INMARSAT got the message. I'd be curious to know if AFRCC > pointed INMARSAT in that direction. > > Really shows the value of precise and stable time references! > > > > > Date: Mon, 24 Mar 2014 16:06:14 -0700 (PDT) > From: "J. Forster" > To:time-nuts@febo.com > Subject: [time-nuts] Airraft Ping Timing > Message-ID: > <13855.12.226.214.5.1395702374.squir...@popaccts.quikus.com> > Content-Type: text/plain;charset=iso-8859-1 > > According to a report on FOX, INMARSAT was able to determine the Malasia > Air followed the southern traectory from the Dopplar of the pings. They > verified their model by tracking other planes. > > -John > > = > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
n1...@dartmouth.edu said: > I am surprised it took them this long. A number of satellite telemetry > systems can use doppler as a matter of course for locating transmitters, > such as Iridium and Argos. It's more complicated than just computing the Doppler. You also have to figure out what the base frequency is and maybe how it changes over time. If you assume the transmit frequency is stable and that the plane is flying in a straight line and you have several samples on a broad enough angle/Doppler spread, you can probably work it all out. For Iridium, the target is fixed (or moving slowly relative to the satellite) and the satellite is moving fast so it gets a lot of angle/Doppler change to work with. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
I am surprised it took them this long. A number of satellite telemetry systems can use doppler as a matter of course for locating transmitters, such as Iridium and Argos. David On 3/25/14 12:58 AM, Peter Gottlieb wrote: This is how ELT locating satellites work (when not relaying the newer GPS data bursts). Several on another list I watch suggested this pretty early on and I guess INMARSAT got the message. I'd be curious to know if AFRCC pointed INMARSAT in that direction. Really shows the value of precise and stable time references! Date: Mon, 24 Mar 2014 16:06:14 -0700 (PDT) From: "J. Forster" To:time-nuts@febo.com Subject: [time-nuts] Airraft Ping Timing Message-ID: <13855.12.226.214.5.1395702374.squir...@popaccts.quikus.com> Content-Type: text/plain;charset=iso-8859-1 According to a report on FOX, INMARSAT was able to determine the Malasia Air followed the southern traectory from the Dopplar of the pings. They verified their model by tracking other planes. -John = ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
On 3/24/14 6:15 PM, Chris Albertson wrote: Yes, word is that they were able to determine the Doppler shift in the plane's signal. I'm surprised this was even recorded but it must have been in the satellite's telemetry downlink. Projecting radial velocity and constraining it to be close to the earth's surface, I guess determines one path and the direction on it. The key they said was getting the doppler shift I used to work in the telemetry business. The experts (not me) would be able to pull information that you'd never think possible from it. And sometimes you have to just be lucky.. For instance, most receivers in space have a "static phase error" telemetry which is basically the voltage going to the VCO in the carrier tracking loop (or the digital equivalent). That can be used to infer doppler, assuming you've taken out all the other things (temperature, etc.). Comparing SPE among multiple signals, with some of them known, would be one way. I'm not saying this is what they did, but it's the kind of thing that if you get lucky, and you happen to have the right telemetry, and you have someone who can figure this stuff out, you can do it. INMARSAT birds are pretty sophisticated, RF wise. They have broad coverage but also some spot beams, so one might be able to do all sorts of things that aren't originally thought of. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Airraft Ping Timing
Yes, word is that they were able to determine the Doppler shift in the plane's signal. I'm surprised this was even recorded but it must have been in the satellite's telemetry downlink. Projecting radial velocity and constraining it to be close to the earth's surface, I guess determines one path and the direction on it. The key they said was getting the doppler shift I used to work in the telemetry business. The experts (not me) would be able to pull information that you'd never think possible from it. On Mon, Mar 24, 2014 at 4:06 PM, J. Forster wrote: > According to a report on FOX, INMARSAT was able to determine the Malasia > Air followed the southern traectory from the Dopplar of the pings. They > verified their model by tracking other planes. > > -John > > = > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
