Re: [time-nuts] Speaking of Costas loops (WAAS)
Hi If there are no receivers using the service (WAAS as a full GPS sat), it's either because: 1) Nobody knows about it 2) It does not work Either way why spend the money to keep it running much better than needed for WAAS simply for it to be there unused? Bob On Jul 10, 2013, at 8:14 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 07/11/2013 01:45 AM, Bob Camp wrote: Hi If the WAAS birds are run in a fashion that gives a true GPS payload performance, why not assign them a SN 32 or below and use them? If the WAAS birds are not in the right numbers, why bother to set them up and spend the bucks to make them behave like a nav sat? What's the payoff? In the old days (receiver channels are sparse resource): If you devote a receiver channel to receive it, let it contribute to position while it provides the core corrections. In todays world: Channels and GPS birds are many, WAAS only contribute to precision and validation. This assuming relatively normal commodity receivers. The fancy receivers (double-frequency, full-blown carrier-phase pseudo-ranges) had little extra use of the WAAS, except possibly somewhat quicker lock-in if not being fed from a national reference grid. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
Hi I read the patent and understand how you can get timing off of a WAAS sat. The carrier does not need to have fancy steering on it to enable that function. The thing that it does not show is doing carrier phase off of a WAAS sat. Bob On Jul 10, 2013, at 9:54 PM, David I. Emery d...@dieconsulting.com wrote: On Wed, Jul 10, 2013 at 07:45:39PM -0400, Bob Camp wrote: Hi If the WAAS birds are run in a fashion that gives a true GPS payload performance, why not assign them a SN 32 or below and use them? If the WAAS birds are not in the right numbers, why bother to set them up and spend the bucks to make them behave like a nav sat? What's the payoff? The patent cited here recently explains... for fixed timing purposes and basic anti jam a simple directional antenna pointed at the WAAS bird allows rejection of many interferers without elaborate and expensive active steered phased array nulling technology. And because - given a known fixed ground position - timing and frequency can work with only one bird visible, this allows timing/frequency using just the WAAS signal (or signals, they do provide more than one WAAS frequency). And potentially if the timing accuracy via the hosted payload is respectable at least for the needs of many fixed time/frequency users this might supply a solution MUCH less resistant to local (nearby) interferers than the usual more or less hemi pattern GPS antenna would - as fixed dishes with considerable gain toward the satellite could be used and in most places they would point well above the horizon and could be shielded by nearby structures to further reduce jamming susceptibility from jammers (intentional or unintentional) below or at the horizon for the site. For timing/frequency users (certainly an important subset of the GPS user population) this provides some protection by antenna pattern that is hard to obtain otherwise (and users interested in higher precision or redundancy of timing could still just use another GPS timing system based on normal hemi GPS antennas as the primary - using the normal SVs - and rely on the dedicated dish pointed at the WAAS bird only as backup in the event of jamming). The choice of using different spreading codes from the normal GPS set for WAAS or using a slightly different one is an overall system architecture decision... which I guess was made in favor of not tying up codes for regular SVs for the WAAS birds. But AFAIK a receiver with suitable firmware could still extract pseudo ranges and use them. I guess there is an issue in any frequency translation scheme with the relationship of carrier and code phase... a homodyne distortion... due to the random phase of the LO(s)... but this too can be predistorted on the ground to come out right and that kept in line via closed loop tracking of the downlink from a ground site. I do understand that this insight into a potential further use of WAAS beyond its use as a data channel and propagation beacon seems to have happened later and not initially. -- 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] Speaking of Costas loops (WAAS)
Hi The pseudo random spreading / looks like noise / buried signal thing is the most common way people piggyback low level signals on a bent pipe. Bob On Jul 11, 2013, at 12:00 AM, David I. Emery d...@dieconsulting.com wrote: On Wed, Jul 10, 2013 at 07:40:50PM -0400, David I. Emery wrote: But if the satellite radiates what a local GPS package would and transmits ephmerides defining its position and motion it could be included in a GPS solution and could be used for timing and frequency purposes the same as any other GPS satellite subject to whatever degree of relative accuracy the bent pipe clock obtains and the degree to which the ephemerides in the format transmitted allow an accurate position to be determined. And from what I have read it seems very likely the WAAS birds meet these criteria.. Thinking some more about the bent pipe repeater aspect of WAAS, aside from allowing any kind of WAAS like signal someone might invent in the future to be retrofitted to existing satellites without a long replacement cycle and expensive launches being involved - there are some interesting properties of the design. One is that one COULD bury in the WAAS uplink cryptographic (eg essentially random to users not in possession of the key) spreading sequence transmissions that would be radiated globally and could be received with unique GPS hardware... such a covert channel in civilian GPS could have various purposes... and would look rather noise like to the rest of the world. -- 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] Speaking of Costas loops (WAAS)
Hi Bob, On 07/11/2013 12:32 PM, Bob Camp wrote: Hi If there are no receivers using the service (WAAS as a full GPS sat), it's either because: 1) Nobody knows about it 2) It does not work Either way why spend the money to keep it running much better than needed for WAAS simply for it to be there unused? There are receivers that produce pseudo-ranges for it [1], and hence can use it in nav solutions. I just found a list of such receivers. The typical receivers does not discloses exactly how they use the WAAS/EGNOS/SBAS signal beyond the obvious correction data. There is also published works on using the WAAS and EGNOS carrier phase reception [2]. There is more if you dig around. [1] Egnos User Guide. http://ec.europa.eu/enterprise/policies/satnav/egnos/files/brochures-leaflets/egnos-user-guide_en.pdf [2] US 6469663. http://www.google.com/patents/US6469663 Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
On 7/11/13 3:36 AM, Bob Camp wrote: Hi The pseudo random spreading / looks like noise / buried signal thing is the most common way people piggyback low level signals on a bent pipe. Assuming that the bent pipe isn't running saturated, which I'm not sure is a valid assumption. Running TWTAs with enough backoff to be linear(ish) consumes a lot more power. I think that most of the transponders on commercial comsats are running linear (or linearized) at least for C and Ku band type applications. However, I wouldn't be so sure for more specialized applications. Consider the S-band Sirius/XM system, they basically designed the satellites for that service, and it could be run saturated, carrying a single high rate data stream that the single channel ground receiver in the car looks at. In fact, a bit of wikipedia research shows that each of the two Sirius satellite broadcasts only one carrier with 4 MHz bandwidth (different frequencies for different satellites). The receiver does both, to get diversity. XM uses 6 frequencies, in a similar scheme. i did find a block diagram of the Sirius payload using google in a book by Elbert (p 267), and while they use a huge pile of TWTAs all combined to radiate about a kilowatt, it does look like they're running two carriers through them (2322.1 and 2330.4 MHz) so they must be running at least somewhat linear. Sirius is S band, but there are also L-band DARS services in other parts of the world. I recall seeing some of the TWTAs for these things in a display case at the tube mfr (Thales, these days) in Ulm, and they are huge beasts. (I'm used to seeing the little helix X, Ku or Ka-band tubes we use for deep space comm or earth observing radar. A dual 300 Watt L-band cavity coupled TWTA is physically quite large.) This doesn't really answer the question about what the payload for WAAS/EGNOS looks like, though. ___ 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] Speaking of Costas loops (WAAS)
Hi Having seen the number of signals being piggybacked on some transponders ( 100,000) it's safe to say that those transponders were not running saturated. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Jim Lux Sent: Thursday, July 11, 2013 10:56 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) On 7/11/13 3:36 AM, Bob Camp wrote: Hi The pseudo random spreading / looks like noise / buried signal thing is the most common way people piggyback low level signals on a bent pipe. Assuming that the bent pipe isn't running saturated, which I'm not sure is a valid assumption. Running TWTAs with enough backoff to be linear(ish) consumes a lot more power. I think that most of the transponders on commercial comsats are running linear (or linearized) at least for C and Ku band type applications. However, I wouldn't be so sure for more specialized applications. Consider the S-band Sirius/XM system, they basically designed the satellites for that service, and it could be run saturated, carrying a single high rate data stream that the single channel ground receiver in the car looks at. In fact, a bit of wikipedia research shows that each of the two Sirius satellite broadcasts only one carrier with 4 MHz bandwidth (different frequencies for different satellites). The receiver does both, to get diversity. XM uses 6 frequencies, in a similar scheme. i did find a block diagram of the Sirius payload using google in a book by Elbert (p 267), and while they use a huge pile of TWTAs all combined to radiate about a kilowatt, it does look like they're running two carriers through them (2322.1 and 2330.4 MHz) so they must be running at least somewhat linear. Sirius is S band, but there are also L-band DARS services in other parts of the world. I recall seeing some of the TWTAs for these things in a display case at the tube mfr (Thales, these days) in Ulm, and they are huge beasts. (I'm used to seeing the little helix X, Ku or Ka-band tubes we use for deep space comm or earth observing radar. A dual 300 Watt L-band cavity coupled TWTA is physically quite large.) This doesn't really answer the question about what the payload for WAAS/EGNOS looks like, though. ___ 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] Speaking of Costas loops (WAAS)
Hi From the US patent: ... and possibility of extending the operating range by allowing increased separation of reference and base receivers by incorporating ionospheric models provided by WAAS To me that says - position data from WAAS, carrier from GPS. - I have not seen a receiver that produces pseudo range for WAAS (as opposed to EGNOS). Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson Sent: Thursday, July 11, 2013 9:25 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) Hi Bob, On 07/11/2013 12:32 PM, Bob Camp wrote: Hi If there are no receivers using the service (WAAS as a full GPS sat), it's either because: 1) Nobody knows about it 2) It does not work Either way why spend the money to keep it running much better than needed for WAAS simply for it to be there unused? There are receivers that produce pseudo-ranges for it [1], and hence can use it in nav solutions. I just found a list of such receivers. The typical receivers does not discloses exactly how they use the WAAS/EGNOS/SBAS signal beyond the obvious correction data. There is also published works on using the WAAS and EGNOS carrier phase reception [2]. There is more if you dig around. [1] Egnos User Guide. http://ec.europa.eu/enterprise/policies/satnav/egnos/files/brochures-leaflet s/egnos-user-guide_en.pdf [2] US 6469663. http://www.google.com/patents/US6469663 Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
Hi From the US patent: ... and possibility of extending the operating range by allowing increased separation of reference and base receivers by incorporating ionospheric models provided by WAAS To me that says - position data from WAAS, carrier from GPS. === I had understood that WAAS provided data such as what were dead or problematic satellites, and ionospheric data which allows the positions derived from standard GPS satellites to be more accurately determined through extra corrections, but WAAS satellite transmissions did not of themselves contribute to to a position determination. Was I wrong in this, or perhaps outdated? Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] Speaking of Costas loops (WAAS)
On 10 Jul, 2013, at 14:08 , David I. Emery d...@dieconsulting.com wrote: It seems completely inconceivable to me that either the antenna system (particularly feeds) or transponder RF hardware on any commercial Ku or C or Ka or X band satellite could possibly be frequency agile enough to tune to 1575.42 MHz unless it was purpose designed to radiate on that frequency from the start. So any hosted WAAS payload is completely application specific. If you look at the pictures here http://www.orbital.com/NewsInfo/Publications/Galaxy_Fact.pdf the satellite on the right has things sticking out the bottom, in the back corner, that are missing on the others and that look a lot like the antennas on GPS satellites. The WAAS satellite is also 350 pounds heavier than the other two even though the C-band payload is identical on all three, so it seems like there could be a fair amount of extra stuff added for WAAS support. Dennis Ferguson ___ 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] Speaking of Costas loops (WAAS)
Hi Yes, this has basically become a debate about weather WAAS sat's do or don't contribute to a directly to a nav solution rather than just provide correction information. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of David J Taylor Sent: Thursday, July 11, 2013 12:57 PM To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) Hi From the US patent: ... and possibility of extending the operating range by allowing increased separation of reference and base receivers by incorporating ionospheric models provided by WAAS To me that says - position data from WAAS, carrier from GPS. === I had understood that WAAS provided data such as what were dead or problematic satellites, and ionospheric data which allows the positions derived from standard GPS satellites to be more accurately determined through extra corrections, but WAAS satellite transmissions did not of themselves contribute to to a position determination. Was I wrong in this, or perhaps outdated? Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] Speaking of Costas loops (WAAS)
If you look at the pictures here http://www.orbital.com/NewsInfo/Publications/Galaxy_Fact.pdf the satellite on the right has things sticking out the bottom, in the back corner, that are missing on the others and that look a lot like the antennas on GPS satellites. The WAAS satellite is also 350 pounds heavier than the other two even though the C-band payload is identical on all three, so it seems like there could be a fair amount of extra stuff added for WAAS support. Dennis Ferguson ___ Thanks, Dennis. The antennas don't surprise me, as they would need to produce a near-whole-disk coverage at a similar ground received power level to the GPS satellites. That extra weight /does/ sound a lot if it were just a simple transponder for earth produced information. Here in Europe was have three EGNOS sources (all on other satellites, I believe), and I don't believe they play any part in actual position fixing, but they do provide extra information enabling the fix to be refined. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] Speaking of Costas loops (WAAS)
Hi It could be 10 pounds of stuff and 340 pounds of shielding … It also could be 10 pounds of WAAS and 340 pounds of something they don't want to talk about. Bob On Jul 11, 2013, at 3:17 PM, David J Taylor david-tay...@blueyonder.co.uk wrote: If you look at the pictures here http://www.orbital.com/NewsInfo/Publications/Galaxy_Fact.pdf the satellite on the right has things sticking out the bottom, in the back corner, that are missing on the others and that look a lot like the antennas on GPS satellites. The WAAS satellite is also 350 pounds heavier than the other two even though the C-band payload is identical on all three, so it seems like there could be a fair amount of extra stuff added for WAAS support. Dennis Ferguson ___ Thanks, Dennis. The antennas don't surprise me, as they would need to produce a near-whole-disk coverage at a similar ground received power level to the GPS satellites. That extra weight /does/ sound a lot if it were just a simple transponder for earth produced information. Here in Europe was have three EGNOS sources (all on other satellites, I believe), and I don't believe they play any part in actual position fixing, but they do provide extra information enabling the fix to be refined. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] Speaking of Costas loops (WAAS)
On 07/09/2013 04:25 AM, Joseph Gwinn wrote: Yes, of course, but I don't think I explained very well. The issue was more economic than technical. There isn't much spare space, weight, or power in the birds, technology moves rapidly, and the satellite companies don't want to have expensive satellites that no longer generate rental income because something became obsolete. So they ruthlessly simplify. A bent pipe will handle any possible band-limited modulation, no matter if currently known or not, and so is the safest solution. Now WAAS may have become important enough to command dedicated hardware, but that came later, to the degree it came at all. A bent pipe is more generic, but there are limits to how much you can alter the output frequency too. If the payload is long-term contracted already when the bird is in the planning stage, then it is another issue. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
On Wed, Jul 10, 2013 at 08:10:45PM +0200, Magnus Danielson wrote: On 07/09/2013 04:25 AM, Joseph Gwinn wrote: Yes, of course, but I don't think I explained very well. The issue was more economic than technical. There isn't much spare space, weight, or power in the birds, technology moves rapidly, and the satellite companies don't want to have expensive satellites that no longer generate rental income because something became obsolete. So they ruthlessly simplify. A bent pipe will handle any possible band-limited modulation, no matter if currently known or not, and so is the safest solution. Now WAAS may have become important enough to command dedicated hardware, but that came later, to the degree it came at all. A bent pipe is more generic, but there are limits to how much you can alter the output frequency too. It seems completely inconceivable to me that either the antenna system (particularly feeds) or transponder RF hardware on any commercial Ku or C or Ka or X band satellite could possibly be frequency agile enough to tune to 1575.42 MHz unless it was purpose designed to radiate on that frequency from the start. So any hosted WAAS payload is completely application specific. What is not clear from anything I have read so far is whether the UPLINK of the modulated WAAS signal is somewhere in the normal (usually 6 GHz for C band satellites) uplink frequency band (probably off one end or the other of the frequency range used). Seems rather likely that the ability to reuse the UPLINK common RF hardware (reflector, feeds, filters, plumbing, maybe transponder front ends and preamps) would make this a very natural design. It also seems clear that doppler and bent pipe conversion oscillator correction is done closed loop by having the ground station that generates the uplinked WAAS signal monitor the downlink from the bird.Obviously correcting for the uplink doppler is a matter of computation from knowing the bird's orbit orbit precisely, something that would certainly be aided by constantly monitoring the range to the bird from that WAAS uplink ground station and maybe another couple (for ionospheric corrections). Apparently the newer stuff uses two L band frequencies to improve this (correct for plasma delay). And the WAAS signal of course allows continuous measurement of range accurately. Correcting for a generally stable but slowly aging conversion oscillator should be pretty straightforward as well, and presumably such a closed loop system could hold the downlink frequency to rather tight tolerances given a reasonably predictable stable oscillator on the bird. The 240 ms up and back delay does make the loop a bit more complex, but the bandwidth is very low I would think since the major perturbation is probably thermal (satellite going into eclipse once a day at certain times, and changes in sun angle over a day). For an observer on the ground it is of course necessary to correct for the satellite orbit induced doppler... which can be up to a couple of hundred Hz or more at 6 GHz - especially with inclined orbit birds such as the INMARSATs. The downlink carrier, while more stable in frequency than GPS bird downlinks is hardly a highly accurate frequency reference on its own. But knowing the geo bird ephemeris (which is broadcast on the WAAS) should allow single signal time and frequency solution for an observer at an accurately known location - by correcting for bird movement. How good the closed loops are relative to the precision clocks on GPS satellites is an interesting question, there seems to be no obvious design need to reach that level of stability... but it does not seem impossible to get pretty close. And much of what has been achieved here seems related to a cost/power trade off in the hosted payload in regards to its reference oscillator. -- 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] Speaking of Costas loops (WAAS)
On 07/10/2013 11:08 PM, David I. Emery wrote: On Wed, Jul 10, 2013 at 08:10:45PM +0200, Magnus Danielson wrote: On 07/09/2013 04:25 AM, Joseph Gwinn wrote: Yes, of course, but I don't think I explained very well. The issue was more economic than technical. There isn't much spare space, weight, or power in the birds, technology moves rapidly, and the satellite companies don't want to have expensive satellites that no longer generate rental income because something became obsolete. So they ruthlessly simplify. A bent pipe will handle any possible band-limited modulation, no matter if currently known or not, and so is the safest solution. Now WAAS may have become important enough to command dedicated hardware, but that came later, to the degree it came at all. A bent pipe is more generic, but there are limits to how much you can alter the output frequency too. It seems completely inconceivable to me that either the antenna system (particularly feeds) or transponder RF hardware on any commercial Ku or C or Ka or X band satellite could possibly be frequency agile enough to tune to 1575.42 MHz unless it was purpose designed to radiate on that frequency from the start. So any hosted WAAS payload is completely application specific. I was thinking along the same lines, but I have too little experience in RF design for birds. There are several potential other uses for L-band transmission if tweaking a little up or down from L1 is feasible, otherwise it's pretty application specific. WAAS links primarily provides an information channel, so it doesn't have to be very accurate. However, as you devote a channel to it, you might as well use it to produce pseudo-ranges, but it seems like they didn't care too much on the carrier-phase part compared to the code-phase, but 10 years back not many receivers used the code phase for nav at all, but carrier smoothed code should at least be common now, so for those it may not fully meet the needs. The added precision for the other channels compensate thought. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
David, While I can easily see how you can do closed loop correctioin for Dopplar from the transmission point for a 'bent pipe' repeater, at any other location that correction would not be valid, because the paths are not parallel. -John = On Wed, Jul 10, 2013 at 08:10:45PM +0200, Magnus Danielson wrote: On 07/09/2013 04:25 AM, Joseph Gwinn wrote: Yes, of course, but I don't think I explained very well. The issue was more economic than technical. There isn't much spare space, weight, or power in the birds, technology moves rapidly, and the satellite companies don't want to have expensive satellites that no longer generate rental income because something became obsolete. So they ruthlessly simplify. A bent pipe will handle any possible band-limited modulation, no matter if currently known or not, and so is the safest solution. Now WAAS may have become important enough to command dedicated hardware, but that came later, to the degree it came at all. A bent pipe is more generic, but there are limits to how much you can alter the output frequency too. It seems completely inconceivable to me that either the antenna system (particularly feeds) or transponder RF hardware on any commercial Ku or C or Ka or X band satellite could possibly be frequency agile enough to tune to 1575.42 MHz unless it was purpose designed to radiate on that frequency from the start. So any hosted WAAS payload is completely application specific. What is not clear from anything I have read so far is whether the UPLINK of the modulated WAAS signal is somewhere in the normal (usually 6 GHz for C band satellites) uplink frequency band (probably off one end or the other of the frequency range used). Seems rather likely that the ability to reuse the UPLINK common RF hardware (reflector, feeds, filters, plumbing, maybe transponder front ends and preamps) would make this a very natural design. It also seems clear that doppler and bent pipe conversion oscillator correction is done closed loop by having the ground station that generates the uplinked WAAS signal monitor the downlink from the bird.Obviously correcting for the uplink doppler is a matter of computation from knowing the bird's orbit orbit precisely, something that would certainly be aided by constantly monitoring the range to the bird from that WAAS uplink ground station and maybe another couple (for ionospheric corrections). Apparently the newer stuff uses two L band frequencies to improve this (correct for plasma delay). And the WAAS signal of course allows continuous measurement of range accurately. Correcting for a generally stable but slowly aging conversion oscillator should be pretty straightforward as well, and presumably such a closed loop system could hold the downlink frequency to rather tight tolerances given a reasonably predictable stable oscillator on the bird. The 240 ms up and back delay does make the loop a bit more complex, but the bandwidth is very low I would think since the major perturbation is probably thermal (satellite going into eclipse once a day at certain times, and changes in sun angle over a day). For an observer on the ground it is of course necessary to correct for the satellite orbit induced doppler... which can be up to a couple of hundred Hz or more at 6 GHz - especially with inclined orbit birds such as the INMARSATs. The downlink carrier, while more stable in frequency than GPS bird downlinks is hardly a highly accurate frequency reference on its own. But knowing the geo bird ephemeris (which is broadcast on the WAAS) should allow single signal time and frequency solution for an observer at an accurately known location - by correcting for bird movement. How good the closed loops are relative to the precision clocks on GPS satellites is an interesting question, there seems to be no obvious design need to reach that level of stability... but it does not seem impossible to get pretty close. And much of what has been achieved here seems related to a cost/power trade off in the hosted payload in regards to its reference oscillator. -- 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] Speaking of Costas loops (WAAS)
Hi On Jul 10, 2013, at 5:08 PM, David I. Emery d...@dieconsulting.com wrote: On Wed, Jul 10, 2013 at 08:10:45PM +0200, Magnus Danielson wrote: On 07/09/2013 04:25 AM, Joseph Gwinn wrote: Yes, of course, but I don't think I explained very well. The issue was more economic than technical. There isn't much spare space, weight, or power in the birds, technology moves rapidly, and the satellite companies don't want to have expensive satellites that no longer generate rental income because something became obsolete. So they ruthlessly simplify. A bent pipe will handle any possible band-limited modulation, no matter if currently known or not, and so is the safest solution. Now WAAS may have become important enough to command dedicated hardware, but that came later, to the degree it came at all. A bent pipe is more generic, but there are limits to how much you can alter the output frequency too. It seems completely inconceivable to me that either the antenna system (particularly feeds) or transponder RF hardware on any commercial Ku or C or Ka or X band satellite could possibly be frequency agile enough to tune to 1575.42 MHz unless it was purpose designed to radiate on that frequency from the start. So any hosted WAAS payload is completely application specific. What is not clear from anything I have read so far is whether the UPLINK of the modulated WAAS signal is somewhere in the normal (usually 6 GHz for C band satellites) uplink frequency band (probably off one end or the other of the frequency range used). Seems rather likely that the ability to reuse the UPLINK common RF hardware (reflector, feeds, filters, plumbing, maybe transponder front ends and preamps) would make this a very natural design. It also seems clear that doppler and bent pipe conversion oscillator correction is done closed loop by having the ground station that generates the uplinked WAAS signal monitor the downlink from the bird. Clear from what documentation? I have not seen anything that says the WAAS is any better than the doppler spec. Uncorrected doppler is still *way* below the level on the nav sats. Why correct it? Obviously correcting for the uplink doppler is a matter of computation from knowing the bird's orbit orbit precisely, something that would certainly be aided by constantly monitoring the range to the bird from that WAAS uplink ground station and maybe another couple (for ionospheric corrections). Apparently the newer stuff uses two L band frequencies to improve this (correct for plasma delay). And the WAAS signal of course allows continuous measurement of range accurately. Correcting for a generally stable but slowly aging conversion oscillator should be pretty straightforward as well, and presumably such a closed loop system could hold the downlink frequency to rather tight tolerances given a reasonably predictable stable oscillator on the bird. The 240 ms up and back delay does make the loop a bit more complex, but the bandwidth is very low I would think since the major perturbation is probably thermal (satellite going into eclipse once a day at certain times, and changes in sun angle over a day). For an observer on the ground it is of course necessary to correct for the satellite orbit induced doppler... which can be up to a couple of hundred Hz or more at 6 GHz - especially with inclined orbit birds such as the INMARSATs. The downlink carrier, while more stable in frequency than GPS bird downlinks is hardly a highly accurate frequency reference on its own. But knowing the geo bird ephemeris (which is broadcast on the WAAS) should allow single signal time and frequency solution for an observer at an accurately known location - by correcting for bird movement. That's only the first layer, you still need atmospheric correction for a low angle bird along with a few other things. How good the closed loops are relative to the precision clocks on GPS satellites is an interesting question, there seems to be no obvious design need to reach that level of stability... but it does not seem impossible to get pretty close. And much of what has been achieved here seems related to a cost/power trade off in the hosted payload in regards to its reference oscillator. I still don't see how it will be as good as a normal GPSDO, let alone better. Bob -- 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] Speaking of Costas loops (WAAS)
On Wed, Jul 10, 2013 at 02:42:19PM -0700, J. Forster wrote: David, While I can easily see how you can do closed loop correctioin for Dopplar from the transmission point for a 'bent pipe' repeater, at any other location that correction would not be valid, because the paths are not parallel. Sorry for my poor choice of words. That is precisely what I meant by for an observer on the ground it is necessary to correct for the satellite orbit induced doppler.This is true for ANY observer, since it would seem certain that the closed loop correction actually is structured and calculated to cause the satellite to radiate a carrier (and timing modulation on it) equivalent to what an accurate local GPS satellite reference clock would generate if one was aboard the hosted payload rather than on the ground. Anything else would make no sense as it is not incumbent on users to try to figure out ground relative timing for some unknown uplink antenna somewhere. And offsetting radiated uplink time and frequency on the ground to make it right on the satellite at the output of the bent pipe repeater is very feasible and more or less a no brainer. But if the satellite radiates what a local GPS package would and transmits ephmerides defining its position and motion it could be included in a GPS solution and could be used for timing and frequency purposes the same as any other GPS satellite subject to whatever degree of relative accuracy the bent pipe clock obtains and the degree to which the ephemerides in the format transmitted allow an accurate position to be determined. And from what I have read it seems very likely the WAAS birds meet these criteria.. -- 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] Speaking of Costas loops (WAAS)
Hi If the WAAS birds are run in a fashion that gives a true GPS payload performance, why not assign them a SN 32 or below and use them? If the WAAS birds are not in the right numbers, why bother to set them up and spend the bucks to make them behave like a nav sat? What's the payoff? Bob On Jul 10, 2013, at 7:40 PM, David I. Emery d...@dieconsulting.com wrote: On Wed, Jul 10, 2013 at 02:42:19PM -0700, J. Forster wrote: David, While I can easily see how you can do closed loop correctioin for Dopplar from the transmission point for a 'bent pipe' repeater, at any other location that correction would not be valid, because the paths are not parallel. Sorry for my poor choice of words. That is precisely what I meant by for an observer on the ground it is necessary to correct for the satellite orbit induced doppler.This is true for ANY observer, since it would seem certain that the closed loop correction actually is structured and calculated to cause the satellite to radiate a carrier (and timing modulation on it) equivalent to what an accurate local GPS satellite reference clock would generate if one was aboard the hosted payload rather than on the ground. Anything else would make no sense as it is not incumbent on users to try to figure out ground relative timing for some unknown uplink antenna somewhere. And offsetting radiated uplink time and frequency on the ground to make it right on the satellite at the output of the bent pipe repeater is very feasible and more or less a no brainer. But if the satellite radiates what a local GPS package would and transmits ephmerides defining its position and motion it could be included in a GPS solution and could be used for timing and frequency purposes the same as any other GPS satellite subject to whatever degree of relative accuracy the bent pipe clock obtains and the degree to which the ephemerides in the format transmitted allow an accurate position to be determined. And from what I have read it seems very likely the WAAS birds meet these criteria.. -- 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] Speaking of Costas loops (WAAS)
On 07/11/2013 01:45 AM, Bob Camp wrote: Hi If the WAAS birds are run in a fashion that gives a true GPS payload performance, why not assign them a SN 32 or below and use them? If the WAAS birds are not in the right numbers, why bother to set them up and spend the bucks to make them behave like a nav sat? What's the payoff? In the old days (receiver channels are sparse resource): If you devote a receiver channel to receive it, let it contribute to position while it provides the core corrections. In todays world: Channels and GPS birds are many, WAAS only contribute to precision and validation. This assuming relatively normal commodity receivers. The fancy receivers (double-frequency, full-blown carrier-phase pseudo-ranges) had little extra use of the WAAS, except possibly somewhat quicker lock-in if not being fed from a national reference grid. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
On Wed, Jul 10, 2013 at 07:45:39PM -0400, Bob Camp wrote: Hi If the WAAS birds are run in a fashion that gives a true GPS payload performance, why not assign them a SN 32 or below and use them? If the WAAS birds are not in the right numbers, why bother to set them up and spend the bucks to make them behave like a nav sat? What's the payoff? The patent cited here recently explains... for fixed timing purposes and basic anti jam a simple directional antenna pointed at the WAAS bird allows rejection of many interferers without elaborate and expensive active steered phased array nulling technology. And because - given a known fixed ground position - timing and frequency can work with only one bird visible, this allows timing/frequency using just the WAAS signal (or signals, they do provide more than one WAAS frequency). And potentially if the timing accuracy via the hosted payload is respectable at least for the needs of many fixed time/frequency users this might supply a solution MUCH less resistant to local (nearby) interferers than the usual more or less hemi pattern GPS antenna would - as fixed dishes with considerable gain toward the satellite could be used and in most places they would point well above the horizon and could be shielded by nearby structures to further reduce jamming susceptibility from jammers (intentional or unintentional) below or at the horizon for the site. For timing/frequency users (certainly an important subset of the GPS user population) this provides some protection by antenna pattern that is hard to obtain otherwise (and users interested in higher precision or redundancy of timing could still just use another GPS timing system based on normal hemi GPS antennas as the primary - using the normal SVs - and rely on the dedicated dish pointed at the WAAS bird only as backup in the event of jamming). The choice of using different spreading codes from the normal GPS set for WAAS or using a slightly different one is an overall system architecture decision... which I guess was made in favor of not tying up codes for regular SVs for the WAAS birds. But AFAIK a receiver with suitable firmware could still extract pseudo ranges and use them. I guess there is an issue in any frequency translation scheme with the relationship of carrier and code phase... a homodyne distortion... due to the random phase of the LO(s)... but this too can be predistorted on the ground to come out right and that kept in line via closed loop tracking of the downlink from a ground site. I do understand that this insight into a potential further use of WAAS beyond its use as a data channel and propagation beacon seems to have happened later and not initially. -- 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] Speaking of Costas loops (WAAS)
On Wed, Jul 10, 2013 at 07:40:50PM -0400, David I. Emery wrote: But if the satellite radiates what a local GPS package would and transmits ephmerides defining its position and motion it could be included in a GPS solution and could be used for timing and frequency purposes the same as any other GPS satellite subject to whatever degree of relative accuracy the bent pipe clock obtains and the degree to which the ephemerides in the format transmitted allow an accurate position to be determined. And from what I have read it seems very likely the WAAS birds meet these criteria.. Thinking some more about the bent pipe repeater aspect of WAAS, aside from allowing any kind of WAAS like signal someone might invent in the future to be retrofitted to existing satellites without a long replacement cycle and expensive launches being involved - there are some interesting properties of the design. One is that one COULD bury in the WAAS uplink cryptographic (eg essentially random to users not in possession of the key) spreading sequence transmissions that would be radiated globally and could be received with unique GPS hardware... such a covert channel in civilian GPS could have various purposes... and would look rather noise like to the rest of the world. -- 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] Speaking of Costas loops (WAAS)
Re: time-nuts Digest, Vol 108, Issue 36 On Sat, 06 Jul 2013 13:59:26 -0400, time-nuts-requ...@febo.com wrote: Message: 5 Date: Sat, 06 Jul 2013 18:57:05 +0200 From: Magnus Danielson mag...@rubidium.dyndns.org To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) Message-ID: 51d84c61.3070...@rubidium.dyndns.org Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 07/06/2013 06:29 PM, Joseph Gwinn wrote: Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? Very unlikely, because then the bird would have to understand every possible code, including those not invented when the bird was launched. If it is within the Gold codes being used for GPS and WAAS, they only need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS specification, as this method is being recommended for receivers. Within that limit, it is relatively cheap to provide code tunability. Yes, of course, but I don't think I explained very well. The issue was more economic than technical. There isn't much spare space, weight, or power in the birds, technology moves rapidly, and the satellite companies don't want to have expensive satellites that no longer generate rental income because something became obsolete. So they ruthlessly simplify. A bent pipe will handle any possible band-limited modulation, no matter if currently known or not, and so is the safest solution. Now WAAS may have become important enough to command dedicated hardware, but that came later, to the degree it came at all. Joe Gwinn ___ 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] Speaking of Costas loops (WAAS)
Jim, you are patialy correct but 99% only talk, never build any thing Bert Kehren Sent from Samsung tabletJim Lux jim...@earthlink.net wrote:On 7/6/13 7:23 PM, Bob Camp wrote: Hi Ok, lets *assume* there is some uber secret gizmo in the sat that makes the unsupervised signal absolutely perfect when transmitted from the sat. The sat still moves relative to the ground. It's speed is a vector in three dimensions (up / down , north / south, east / west). Depending on your location relative to the sat, the doppler will be different. A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. It'll do much better over long time spans. At 1.5 GHz, that would be 0.015 Hz. If doppler is in the 50 to 100 Hz range, you need to cancel it by 1000:1 simply to get the carrier as good as a simple GPSDO. That's going to require accurate position data on the sat, it's velocity (all real time), and your location. - Next you need data on the rest of the constellation. They fly in the same space as the WAAS birds, and transmit on the same frequencies. As they pass within the capture area of your antenna you will need a way to figure out which is the GPS and which is the WAAS sat. The easy way to do that would be to run a GPS to get all the data and then process it….. Dish costs something Downconverter costs something Signal processing the received signal costs something You still need a GPS You still need a good local OCXO as a flywheel It's going to be tough to convince me that's any cheaper than a GPSDO I think you're right.. But time-nuts don't always go for the easy 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. ___ 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] Speaking of Costas loops (WAAS)
Hi everyone, Have not seen a reference to either the Fenton patent nor the Fruehof paper, which discuss using WAAS for timing with a dish antenna. http://www.freqelec.com/gps_gnss/waas_for_telecom_wp_5-06.pdf https://www.google.com/patents/US6445340 kind regards, Björn ___ 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] Speaking of Costas loops (WAAS)
I have a dish. I have several GPSDOs, some I built myself. I just think it would be a fun thing to try. It will not beat the performance of my GPSDOs or rubidium oscillators. Someone with a micrometer still has use for a yard stick. Yesterday, I worked on the dish feed. I checked the polarization sense and figured out a way to mount it to the dish. Next week or early August, I hope to have made an adjustable elevation/azimuth mount for the dish. Maybe by fall I could have some interesting results to share. Just having fun with time science. Heck, I even toy with tuning fork oscillators and I hope to build a nice pendulum clock myself someday! John WA4WDL -- From: Bob Camp li...@rtty.us Sent: Saturday, July 06, 2013 10:23 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) Hi Ok, lets *assume* there is some uber secret gizmo in the sat that makes the unsupervised signal absolutely perfect when transmitted from the sat. The sat still moves relative to the ground. It's speed is a vector in three dimensions (up / down , north / south, east / west). Depending on your location relative to the sat, the doppler will be different. A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. It'll do much better over long time spans. At 1.5 GHz, that would be 0.015 Hz. If doppler is in the 50 to 100 Hz range, you need to cancel it by 1000:1 simply to get the carrier as good as a simple GPSDO. That's going to require accurate position data on the sat, it's velocity (all real time), and your location. - Next you need data on the rest of the constellation. They fly in the same space as the WAAS birds, and transmit on the same frequencies. As they pass within the capture area of your antenna you will need a way to figure out which is the GPS and which is the WAAS sat. The easy way to do that would be to run a GPS to get all the data and then process it….. Dish costs something Downconverter costs something Signal processing the received signal costs something You still need a GPS You still need a good local OCXO as a flywheel It's going to be tough to convince me that's any cheaper than a GPSDO - Lots of things to slog through. I suspect there are other sat signals that are better candidates. Bob On Jul 6, 2013, at 2:23 PM, jmfranke jmfra...@cox.net wrote: A lot of the changes from bent pipe to the new system including C-band uplink is explained here: http://www.insidegnss.com/node/697 While there, downlink the extended PDF version. John WA4WDL -- From: Magnus Danielson mag...@rubidium.dyndns.org Sent: Saturday, July 06, 2013 12:57 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) On 07/06/2013 06:29 PM, Joseph Gwinn wrote: Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? Very unlikely, because then the bird would have to understand every possible code, including those not invented when the bird was launched. If it is within the Gold codes being used for GPS and WAAS, they only need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS specification, as this method is being recommended for receivers. Within that limit, it is relatively cheap to provide code tunability. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
Re: time-nuts Digest, Vol 108, Issue 29 On Fri, 05 Jul 2013 19:55:42 -0400, time-nuts-requ...@febo.com wrote: Message: 6 Date: Sat, 06 Jul 2013 00:27:33 +0200 From: Magnus Danielson mag...@rubidium.dyndns.org To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops Message-ID: 51d74855.9090...@rubidium.dyndns.org Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 07/05/2013 10:39 PM, Joseph Gwinn wrote: Re: time-nuts Digest, Vol 108, Issue 28 Message: 2 Date: Fri, 05 Jul 2013 09:18:39 -0700 From: Jim Luxjim...@earthlink.net To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops Message-ID:51d6f1df.9090...@earthlink.net Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 7/5/13 8:44 AM, Bob Stewart wrote: Wouldn't a Cs or Rb clock in orbit be slow due to relativistic effects? I'm pretty sure there is a relativistic correction to the GPS clocks. Bob - AE6RV I believe that the original WAAS repurposed transponders intended for other L-band satellite signals (e.g. Sirius/XM/LightSquared). As noted earlier in the discussion, the new satellites might have a specialized payload, which could have a purpose specific coherent transponder, rather than a linear translator. If it is purpose specific and single channel, then making it immune to the local oscillator is straightforward. I worked on a proposal for the original WAAS system. The WAAS signal is not a timing signal in the sense that GPS signals from space are timing signals. WAAS instead sends out a stream of correction data that allows one to greatly improve the accuracy and reliability of GPS signals. So, unless things have changed greatly, the geostationary satellite that broadcasts the WAAS signal need not have an atomic clock. This is naturally still true, but we are into the level of there's a signal here, what can we use it for?. Doing a much simplified receiver could serve some well enough, without going the full monty. It's like taking the color-carrier of analog TV broadcasts. OK. Given that the birds WAAS uses were built for communications purposes, not timing purposes, I'g guess that their frequency reference is a very good quartz unit. I suppose Rubidium is possible, but Cesium is very unlikely. Bent-pipe channels do a frequency change to eliminate singing. I imagine the datasheet for the rentable comm channels will give the frequency error and stability of the downlink signal. Joe Gwinn ___ 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] Speaking of Costas loops (WAAS)
http://www.navipedia.net/index.php/WAAS_Signal_Structure Doppler Shift: The Doppler shift, as perceived by a stationary user, on the signal broadcast by WAAS GEOs is less than 40 meters per second (?210 Hz at L1) in the worst case (at the end of life of the GEOs). Carrier Frequency Stability: The short term stability of the carrier frequency (square root of the Allan Variance) at the input of the user´s receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding the effects of the ionosphere and Doppler. Polarization: The broadcast signal is right-handed circularly polarized. The ellipticity will be no worse than 2 dB for the angular range of ±9.1o from boresight. Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). Correlation Loss: Correlation loss is defined as the ratio of output powers from a perfect correlator for two cases: 1) the actual receiver WAAS signal correlated against a perfect unfiltered PN reference, or 2) a perfect unfiltered PN signal normalized to the same total power as the WAAS signal in case 1. The correlation loss resulting from modulation imperfections and filtering inside the WAAS satellite payload is less than 1 dB. John WA4WDL -- From: Joseph Gwinn joegw...@comcast.net Sent: Saturday, July 06, 2013 10:50 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) Re: time-nuts Digest, Vol 108, Issue 29 On Fri, 05 Jul 2013 19:55:42 -0400, time-nuts-requ...@febo.com wrote: Message: 6 Date: Sat, 06 Jul 2013 00:27:33 +0200 From: Magnus Danielson mag...@rubidium.dyndns.org To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops Message-ID: 51d74855.9090...@rubidium.dyndns.org Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 07/05/2013 10:39 PM, Joseph Gwinn wrote: Re: time-nuts Digest, Vol 108, Issue 28 Message: 2 Date: Fri, 05 Jul 2013 09:18:39 -0700 From: Jim Luxjim...@earthlink.net To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops Message-ID:51d6f1df.9090...@earthlink.net Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 7/5/13 8:44 AM, Bob Stewart wrote: Wouldn't a Cs or Rb clock in orbit be slow due to relativistic effects? I'm pretty sure there is a relativistic correction to the GPS clocks. Bob - AE6RV I believe that the original WAAS repurposed transponders intended for other L-band satellite signals (e.g. Sirius/XM/LightSquared). As noted earlier in the discussion, the new satellites might have a specialized payload, which could have a purpose specific coherent transponder, rather than a linear translator. If it is purpose specific and single channel, then making it immune to the local oscillator is straightforward. I worked on a proposal for the original WAAS system. The WAAS signal is not a timing signal in the sense that GPS signals from space are timing signals. WAAS instead sends out a stream of correction data that allows one to greatly improve the accuracy and reliability of GPS signals. So, unless things have changed greatly, the geostationary satellite that broadcasts the WAAS signal need not have an atomic clock. This is naturally still true, but we are into the level of there's a signal here, what can we use it for?. Doing a much simplified receiver could serve some well enough, without going the full monty. It's like taking the color-carrier of analog TV broadcasts. OK. Given that the birds WAAS uses were built for communications purposes, not timing purposes, I'g guess that their frequency reference is a very good quartz unit. I suppose Rubidium is possible, but Cesium is very unlikely. Bent-pipe channels do a frequency change to eliminate singing. I imagine the datasheet for the rentable comm channels will give the frequency error and stability of the downlink signal. Joe Gwinn ___ 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] Speaking of Costas loops (WAAS)
On 7/6/13 8:10 AM, jmfranke wrote: http://www.navipedia.net/index.php/WAAS_Signal_Structure Doppler Shift: The Doppler shift, as perceived by a stationary user, on the signal broadcast by WAAS GEOs is less than 40 meters per second (?210 Hz at L1) in the worst case (at the end of life of the GEOs). That is more a requirement on the spacecraft. Precompensation from the ground won't work... if the satellite is driving West, then users to the west see the frequency go up, and users to the east see it go down. Carrier Frequency Stability: The short term stability of the carrier frequency (square root of the Allan Variance) at the input of the user´s receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding the effects of the ionosphere and Doppler. that sounds like comparable to a decent OCXO (10811A, etc.) Polarization: The broadcast signal is right-handed circularly polarized. The ellipticity will be no worse than 2 dB for the angular range of ±9.1o from boresight. Antenna spec.. Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? ___ 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] Speaking of Costas loops (WAAS)
On 7/6/13 7:50 AM, Joseph Gwinn wrote: Re: time-nuts Digest, Vol 108, Issue 29 On Fri, 05 Jul 2013 19:55:42 -0400, time-nuts-requ...@febo.com wrote: OK. Given that the birds WAAS uses were built for communications purposes, not timing purposes, I'g guess that their frequency reference is a very good quartz unit. I suppose Rubidium is possible, but Cesium is very unlikely. Except that apparently, the WAAS/EGNOS repeater payload is purpose designed, so it isn't necessarily the same bent pipe as is used for other purposes, although it could be: similar to other Mobile Satellite Service channels for instance. I would think it very unlikely they are flying either Rb or Cs. If they need high stability and precision, then they'd just recover the carrier from the uplink signal, because that could be as steady as you like it. I would think it would be cheaper to do that than to put an atomic reference up. Bent-pipe channels do a frequency change to eliminate singing. I imagine the datasheet for the rentable comm channels will give the frequency error and stability of the downlink signal. The international allocations for up and down frequencies are separated by quite a bit (Earth to Space and Space to Earth, respectively). For C band, up is around 6 GHz and down is around 4 GHz. That makes building a filter to separate them pretty easy. So the WAAS signal goes up on 4 and comes down on 1.5. What is really needed is a good description of the WAAS/EGNOS system, because it will give all those nice gory details. ___ 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] Speaking of Costas loops (WAAS)
Re: time-nuts Digest, Vol 108, Issue 35 On Sat, 06 Jul 2013 12:00:01 -0400, time-nuts-requ...@febo.com wrote: Message: 5 Date: Sat, 06 Jul 2013 08:56:46 -0700 From: Jim Lux jim...@earthlink.net To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) Message-ID: 51d83e3e.2050...@earthlink.net Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 7/6/13 8:10 AM, jmfranke wrote: http://www.navipedia.net/index.php/WAAS_Signal_Structure Doppler Shift: The Doppler shift, as perceived by a stationary user, on the signal broadcast by WAAS GEOs is less than 40 meters per second (?210 Hz at L1) in the worst case (at the end of life of the GEOs). That is more a requirement on the spacecraft. Precompensation from the ground won't work... if the satellite is driving West, then users to the west see the frequency go up, and users to the east see it go down. Carrier Frequency Stability: The short term stability of the carrier frequency (square root of the Allan Variance) at the input of the user?s receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding the effects of the ionosphere and Doppler. that sounds like comparable to a decent OCXO (10811A, etc.) Polarization: The broadcast signal is right-handed circularly polarized. The ellipticity will be no worse than 2 dB for the angular range of ?9.1o from boresight. Antenna spec.. Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? Very unlikely, because then the bird would have to understand every possible code, including those not invented when the bird was launched. Joe Gwinn ___ 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] Speaking of Costas loops (WAAS)
On 07/06/2013 06:29 PM, Joseph Gwinn wrote: Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? Very unlikely, because then the bird would have to understand every possible code, including those not invented when the bird was launched. If it is within the Gold codes being used for GPS and WAAS, they only need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS specification, as this method is being recommended for receivers. Within that limit, it is relatively cheap to provide code tunability. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
A lot of the changes from bent pipe to the new system including C-band uplink is explained here: http://www.insidegnss.com/node/697 While there, downlink the extended PDF version. John WA4WDL -- From: Magnus Danielson mag...@rubidium.dyndns.org Sent: Saturday, July 06, 2013 12:57 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) On 07/06/2013 06:29 PM, Joseph Gwinn wrote: Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? Very unlikely, because then the bird would have to understand every possible code, including those not invented when the bird was launched. If it is within the Gold codes being used for GPS and WAAS, they only need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS specification, as this method is being recommended for receivers. Within that limit, it is relatively cheap to provide code tunability. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
-- From: jmfranke jmfra...@cox.net Sent: Saturday, July 06, 2013 2:09 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) A lot of the changes from bent pipe to the new system including C-band uplink is explained here: http://www.insidegnss.com/node/697 While there, downlink the extended PDF version. John WA4WDL -- From: Magnus Danielson mag...@rubidium.dyndns.org Sent: Saturday, July 06, 2013 12:57 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) On 07/06/2013 06:29 PM, Joseph Gwinn wrote: Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? Very unlikely, because then the bird would have to understand every possible code, including those not invented when the bird was launched. If it is within the Gold codes being used for GPS and WAAS, they only need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS specification, as this method is being recommended for receivers. Within that limit, it is relatively cheap to provide code tunability. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
A lot of the changes from bent pipe to the new system including C-band uplink is explained here: http://www.insidegnss.com/node/697 While there, downlink the extended PDF version. John WA4WDL -- From: Magnus Danielson mag...@rubidium.dyndns.org Sent: Saturday, July 06, 2013 12:57 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) On 07/06/2013 06:29 PM, Joseph Gwinn wrote: Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? Very unlikely, because then the bird would have to understand every possible code, including those not invented when the bird was launched. If it is within the Gold codes being used for GPS and WAAS, they only need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS specification, as this method is being recommended for receivers. Within that limit, it is relatively cheap to provide code tunability. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
Sorry about the duplicates, email issue. John WA4WDL ___ 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] Speaking of Costas loops (WAAS)
On 7/6/13 9:29 AM, Joseph Gwinn wrote: Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? Very unlikely, because then the bird would have to understand every possible code, including those not invented when the bird was launched. the class of codes used is pretty restricted (e.g. Gold/Kasami codes with 10 bit generators), at least for GPS. Most correlator and generator implementations are somewhat programmable, at least as far as the tap configuration and the initial load. ___ 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] Speaking of Costas loops (WAAS)
Hi Ok, lets *assume* there is some uber secret gizmo in the sat that makes the unsupervised signal absolutely perfect when transmitted from the sat. The sat still moves relative to the ground. It's speed is a vector in three dimensions (up / down , north / south, east / west). Depending on your location relative to the sat, the doppler will be different. A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. It'll do much better over long time spans. At 1.5 GHz, that would be 0.015 Hz. If doppler is in the 50 to 100 Hz range, you need to cancel it by 1000:1 simply to get the carrier as good as a simple GPSDO. That's going to require accurate position data on the sat, it's velocity (all real time), and your location. - Next you need data on the rest of the constellation. They fly in the same space as the WAAS birds, and transmit on the same frequencies. As they pass within the capture area of your antenna you will need a way to figure out which is the GPS and which is the WAAS sat. The easy way to do that would be to run a GPS to get all the data and then process it….. Dish costs something Downconverter costs something Signal processing the received signal costs something You still need a GPS You still need a good local OCXO as a flywheel It's going to be tough to convince me that's any cheaper than a GPSDO - Lots of things to slog through. I suspect there are other sat signals that are better candidates. Bob On Jul 6, 2013, at 2:23 PM, jmfranke jmfra...@cox.net wrote: A lot of the changes from bent pipe to the new system including C-band uplink is explained here: http://www.insidegnss.com/node/697 While there, downlink the extended PDF version. John WA4WDL -- From: Magnus Danielson mag...@rubidium.dyndns.org Sent: Saturday, July 06, 2013 12:57 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) On 07/06/2013 06:29 PM, Joseph Gwinn wrote: Code/Carrier Frequency Coherence: The lack of coherence between the broadcast carrier phase and the code phase shall be limited. The short term (10sec) fractional frequency difference between the code phase rate and the carrier frequency shall be less than 5x10-11 (one sigma). Over the long term (100 sec), the difference between the change in the broadcast code phase (convert to carrier cycles) and the change in the broadcast carrier phase shall be within one carrier cycle (one sigma). This is interesting. Does it imply that they regenerate the code on board? Very unlikely, because then the bird would have to understand every possible code, including those not invented when the bird was launched. If it is within the Gold codes being used for GPS and WAAS, they only need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS specification, as this method is being recommended for receivers. Within that limit, it is relatively cheap to provide code tunability. Cheers, Magnus ___ 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] Speaking of Costas loops (WAAS)
On 7/6/13 7:23 PM, Bob Camp wrote: Hi Ok, lets *assume* there is some uber secret gizmo in the sat that makes the unsupervised signal absolutely perfect when transmitted from the sat. The sat still moves relative to the ground. It's speed is a vector in three dimensions (up / down , north / south, east / west). Depending on your location relative to the sat, the doppler will be different. A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. It'll do much better over long time spans. At 1.5 GHz, that would be 0.015 Hz. If doppler is in the 50 to 100 Hz range, you need to cancel it by 1000:1 simply to get the carrier as good as a simple GPSDO. That's going to require accurate position data on the sat, it's velocity (all real time), and your location. - Next you need data on the rest of the constellation. They fly in the same space as the WAAS birds, and transmit on the same frequencies. As they pass within the capture area of your antenna you will need a way to figure out which is the GPS and which is the WAAS sat. The easy way to do that would be to run a GPS to get all the data and then process it….. Dish costs something Downconverter costs something Signal processing the received signal costs something You still need a GPS You still need a good local OCXO as a flywheel It's going to be tough to convince me that's any cheaper than a GPSDO I think you're right.. But time-nuts don't always go for the easy 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.
