On Tue, 18 Sep 2012 05:23:16 -0700, MrTallyman <MrTallyman@BananaCountersRUs.org> wrote:>On Tue, 18 Sep 2012 10:18:50 +0100, Pomegranate Bastard ><pommyB@dsl.pipex.com> wrote: > >>On Sun, 16 Sep 2012 08:36:33 -0700, John Larkin >><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Sat, 15 Sep 2012 22:17:57 -0700, MrTallyman >>><MrTallyman@BananaCountersRUs.org> wrote: >>> >>>>On Sat, 15 Sep 2012 20:02:34 -0700, John Larkin >>>><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>>>On Sun, 16 Sep 2012 00:03:50 +0000 (UTC), Jim Whitby >>>>><james@jameswhitby.org> wrote: >>>>> >>>>>>I'm asking this here in the hope someone knows something about GPS >>>>>>receivers. >>>>>> >>>>>>I'm a decent tech, but not an engineer... >>>>>> >>>>>>I have a Tomtom 2535 gps. Nice unit blah blah. >>>>>> >>>>>>Some ( software? ) engineer decided to change the gps info display. It >>>>>>now contains a pic of earth with dots for satellites instead of a bar >>>>>>graph. Ok. No biggie. >>>>> >>>>>A software engineer probably doesn't know what a dB is. >>>> >>>> You're an idiot. >>> >>>OK, explain to us what a dB is. >> >>How would a toilet cleaner know that? > > Try to tell us, since that is what *you* do for a living. > > As for myself... > > When I adjust the waveguide output channel of a high power satellite >transceiver, my employer is quite comfortable with my understanding of >logarithmic progression. Also when I adjust the noise source loop that >we pump it with for the test. > > You are lost. > > As for you... > > When you adjust your mop head, be sure to bring it right up next to >your face so your crabs and fleas can hop onto it and migrate to new^ SOME of your crabs and fleas. We wouldn't want you to go completely without friends.>horizons. Good job of spreading the vermin, you immature little retarded >characterless honorless bastard. Go back to the kook group, dumbfuck.
signal strength on a GPS
Started by ●September 15, 2012
Reply by ●September 18, 20122012-09-18
Reply by ●September 18, 20122012-09-18
On Tue, 18 Sep 2012 07:50:35 GMT, Jan Panteltje <pNaonStpealmtje@yahoo.com> wrote:>On a sunny day (Mon, 17 Sep 2012 23:42:23 +0300) it happened >upsidedown@downunder.com wrote in ><ci2f58t5mbaljorvassqg3j52s1nmiihp3@4ax.com>: > >>So in reality, you need four independent signal strength signals for >>the best (geometry) four satellites > >? >You need 3 sats for a 2D position, and 4 sats for a 3D position solution.Three variables require three equations; four, four. Don't forget time.
Reply by ●September 18, 20122012-09-18
On Tue, 18 Sep 2012 05:34:00 -0700, MrTallyman <MrTallyman@BananaCountersRUs.org> wrote:>On Tue, 18 Sep 2012 05:23:16 -0700, MrTallyman ><MrTallyman@BananaCountersRUs.org> wrote: > >>On Tue, 18 Sep 2012 10:18:50 +0100, Pomegranate Bastard >><pommyB@dsl.pipex.com> wrote: >> >>>On Sun, 16 Sep 2012 08:36:33 -0700, John Larkin >>><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Sat, 15 Sep 2012 22:17:57 -0700, MrTallyman >>>><MrTallyman@BananaCountersRUs.org> wrote: >>>> >>>>>On Sat, 15 Sep 2012 20:02:34 -0700, John Larkin >>>>><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >>>>> >>>>>>On Sun, 16 Sep 2012 00:03:50 +0000 (UTC), Jim Whitby >>>>>><james@jameswhitby.org> wrote: >>>>>> >>>>>>>I'm asking this here in the hope someone knows something about GPS >>>>>>>receivers. >>>>>>> >>>>>>>I'm a decent tech, but not an engineer... >>>>>>> >>>>>>>I have a Tomtom 2535 gps. Nice unit blah blah. >>>>>>> >>>>>>>Some ( software? ) engineer decided to change the gps info display. It >>>>>>>now contains a pic of earth with dots for satellites instead of a bar >>>>>>>graph. Ok. No biggie. >>>>>> >>>>>>A software engineer probably doesn't know what a dB is. >>>>> >>>>> You're an idiot. >>>> >>>>OK, explain to us what a dB is. >>> >>>How would a toilet cleaner know that? >> >> Try to tell us, since that is what *you* do for a living. >> >> As for myself... >> >> When I adjust the waveguide output channel of a high power satellite >>transceiver, my employer is quite comfortable with my understanding of >>logarithmic progression. Also when I adjust the noise source loop that >>we pump it with for the test. >> >> You are lost. >> >> As for you... >> >> When you adjust your mop head, be sure to bring it right up next to >>your face so your crabs and fleas can hop onto it and migrate to new > ^ > SOME of your crabs and fleas. We wouldn't want you to go >completely without friends. > >>horizons. Good job of spreading the vermin, you immature little retarded >>characterless honorless bastard. Go back to the kook group, dumbfuck.By the way, Nymbecile, have they given you a toilet brush yet? Or are you still having to use your tongue?
Reply by ●September 18, 20122012-09-18
On Tue, 18 Sep 2012 05:23:16 -0700, MrTallyman <MrTallyman@BananaCountersRUs.org> wrote:>On Tue, 18 Sep 2012 10:18:50 +0100, Pomegranate Bastard ><pommyB@dsl.pipex.com> wrote: > >>On Sun, 16 Sep 2012 08:36:33 -0700, John Larkin >><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Sat, 15 Sep 2012 22:17:57 -0700, MrTallyman >>><MrTallyman@BananaCountersRUs.org> wrote: >>> >>>>On Sat, 15 Sep 2012 20:02:34 -0700, John Larkin >>>><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>>>On Sun, 16 Sep 2012 00:03:50 +0000 (UTC), Jim Whitby >>>>><james@jameswhitby.org> wrote: >>>>> >>>>>>I'm asking this here in the hope someone knows something about GPS >>>>>>receivers. >>>>>> >>>>>>I'm a decent tech, but not an engineer... >>>>>> >>>>>>I have a Tomtom 2535 gps. Nice unit blah blah. >>>>>> >>>>>>Some ( software? ) engineer decided to change the gps info display. It >>>>>>now contains a pic of earth with dots for satellites instead of a bar >>>>>>graph. Ok. No biggie. >>>>> >>>>>A software engineer probably doesn't know what a dB is. >>>> >>>> You're an idiot. >>> >>>OK, explain to us what a dB is. >> >>How would a toilet cleaner know that? > > Try to tell us, since that is what *you* do for a living. > > As for myself... > > When I adjust the waveguide output channel of a high power satellite >transceiver, my employer is quite comfortable with my understanding of >logarithmic progression. Also when I adjust the noise source loop that >we pump it with for the test. > > You are lost. > > As for you... > > When you adjust your mop head, be sure to bring it right up next to >your face so your crabs and fleas can hop onto it and migrate to new >horizons. Good job of spreading the vermin, you immature little retarded >characterless honorless bastard. Go back to the kook group, dumbfuck.Sadly this has become a kook group, thanks to you.
Reply by ●September 18, 20122012-09-18
On a sunny day (Tue, 18 Sep 2012 10:44:15 -0400) it happened "krw@att.bizzzzzzzzzzzz" <krw@att.bizzzzzzzzzzzz> wrote in <q42h5890musoiq20nq2g7lea8rao7v203h@4ax.com>:>On Tue, 18 Sep 2012 07:50:35 GMT, Jan Panteltje <pNaonStpealmtje@yahoo.com> >wrote: > >>On a sunny day (Mon, 17 Sep 2012 23:42:23 +0300) it happened >>upsidedown@downunder.com wrote in >><ci2f58t5mbaljorvassqg3j52s1nmiihp3@4ax.com>: >> >>>So in reality, you need four independent signal strength signals for >>>the best (geometry) four satellites >> >>? >>You need 3 sats for a 2D position, and 4 sats for a 3D position solution. > >Three variables require three equations; four, four. Don't forget time. >Here is partial output from my software GPSPwith teh dealextreme GPS moduke with only 3 sats, it immediately goes to 2D mode: date and time 2012 9 18 17:7-24 UTC Mode 2D GPS SPS Mode, fix valid pdop 11.8 hdop 11.4 vdop 3.2 satellites used 3 ( 6 3 19 ) satellites in view 12 id 19 * elevation 65 azimuth 166 snr 32 id 11 elevation 62 azimuth 274 snr 0 id 1 elevation 44 azimuth 273 snr 0 id 22 elevation 43 azimuth 63 snr 0 id 3 * elevation 32 azimuth 159 snr 27 id 14 elevation 31 azimuth 98 snr 0 id 32 elevation 31 azimuth 206 snr 0 id 28 elevation 23 azimuth 315 snr 0 id 6 * elevation 22 azimuth 149 snr 24 id 18 elevation 6 azimuth 49 snr 0 id 27 elevation 5 azimuth 13 snr 0 id 20 elevation 5 azimuth 222 snr 0 I left out the location to protect against Miss Iles... -------------------- As soon as it has signal on 4 sats it goes to 3D mode, so gives altitude too. This is just parsed from the NEMEA data. The low snr is not realy bad, you do not get much more in practice: http://www.s5tech.net/s53mv/navsats/theory.html
Reply by ●September 18, 20122012-09-18
On Saturday, September 15, 2012 8:03:50 PM UTC-4, Jim Whitby wrote:> I'm asking this here in the hope someone knows something about GPS=20 > receivers. >=20[snip]> Does anyone have a clue what 100% is relative to? >=20Well, it's not going to be SINAD since it's not an analog receiver. Your choices are most likely Bit Error Rate (BER), though a BER of 20% woul= d seem completely unusable to me. The other option is C/I+N but again, tha= t's used more for analog modulation schemes (or should be, though some comp= anies think SINAD is acceptable for "digital modulation". These people sho= uld be tarred and feathered. You could write a book about modulation schem= es and their effect on BER, and I'm sure some have. I've never found dBm l= ookup tables to be particularly good descriptors for BER. Your mileage may= vary. Bars and SINAD and I+N values aside, if the GPS fades too much, there's pro= bably something wrong with the receiver or the placement of its antenna. S= ome antennas are powered (i.e., internal active preamps), so you might veri= fy the batteries are fresh, or it's otherwise powered-up with the correct v= oltage. Shameless plug: We use a lot of Garmin Montana GPS's (650's and 650t's)for= our field work. Expensive, but perfect for what we do. Of course, as wit= h any early adopter there were some early software glitches; like "Continue= four-thousand one-hundred fifty miles, then make a U-turn", but they squas= hed that bug pretty quick. :)
Reply by ●September 19, 20122012-09-19
On a sunny day (Tue, 18 Sep 2012 19:35:15 -0700 (PDT)) it happened mpm <mpmillard@aol.com> wrote in <c99847af-e37f-4cfa-9fe3-a47a62d60f3f@googlegroups.com>:>On Saturday, September 15, 2012 8:03:50 PM UTC-4, Jim Whitby wrote: >> I'm asking this here in the hope someone knows something about GPS >> receivers. >> >[snip] > >> Does anyone have a clue what 100% is relative to? >> > >Well, it's not going to be SINAD since it's not an analog receiver. >Your choices are most likely Bit Error Rate (BER), though a BER of 20% woul= >d seem completely unusable to me. The other option is C/I+N but again, tha= >t's used more for analog modulation schemes (or should be, though some comp= >anies think SINAD is acceptable for "digital modulation". These people sho= >uld be tarred and feathered. You could write a book about modulation schem= >es and their effect on BER, and I'm sure some have. I've never found dBm l= >ookup tables to be particularly good descriptors for BER. Your mileage may= > vary. > >Bars and SINAD and I+N values aside, if the GPS fades too much, there's pro= >bably something wrong with the receiver or the placement of its antenna. S= >ome antennas are powered (i.e., internal active preamps), so you might veri= >fy the batteries are fresh, or it's otherwise powered-up with the correct v= >oltage. > >Shameless plug: We use a lot of Garmin Montana GPS's (650's and 650t's)for= > our field work. Expensive, but perfect for what we do. Of course, as wit= >h any early adopter there were some early software glitches; like "Continue= > four-thousand one-hundred fifty miles, then make a U-turn", but they squas= >hed that bug pretty quick. :)If you use ANY GPS receiver that has a NEMEA output, the data we are talking about is standarized in the RS232 'GPGSV' message: This is the offcial NEMEA standard, for that GPGSV message, it shows an example message and the meaning of the comma separated fields in it. /* test for SV-GNSS Satellites in View */ /* GSV-GNSS Satellites in View Table B-8 contains the values for the following example: $GPGSV,2,1,07,07,79,048,42,02,51,062,43,26,36,256,42,27,27,138,42*71 $GPGSV,2,2,07,09,23,313,42,04,19,159,41,15,12,041,42*41 Table B-8 GSV Data Format Name Example Description Message ID $GPGSV GSV protocol header Number of Messages1 2 Range 1 to 3 Message Number1 1 Range 1 to 3 Satellites in View 07 Satellite ID 07 Channel 1(Range 1 to 32) Elevation 79 degrees Channel 1(Maximum90) Azimuth 048 degrees Channel 1(True, Range 0 to 359) SNR(C/No) 42 dBHz Range 0 to 99,null when not tracking <------------------------------------------- ....... ....... Satellite ID 27 Channel 4 (Range 1 to 32) Elevation 27 Degrees Channel 4(Maximum90) Azimuth 138 Degrees Channel 4(True, Range 0 to 359) SNR(C/No) 42 dBHz Range 0 to 99,null when not tracking <------------------------------------------- Checksum *71 <CR><LF> End of message termination Depending on the number of satellites tracked multiple messages of GSV data may be required. */ You will note, that as the OP noticed, his GPS now confirms to this standard, as his signal to noise is displayed as 0-100% for each satellite, see large arrows. Linux source code of my gpspc program (that this came from) is availabe upon request, but be aware that it also interfaces to other modules like for magnetic compass, air pressure, temperature, and has an interface for auto-pilot, and supports multiple waypoints. If you want the details for all NEMEA messages look on the web for the SiRF chipset NEMEA reference manual. I will leave it at that...
Reply by ●September 20, 20122012-09-20
On Mon, 17 Sep 2012 08:01:03 GMT, Jan Panteltje <pNaonStpealmtje@yahoo.com> wrote:>On a sunny day (Mon, 17 Sep 2012 08:30:48 +0300) it happened >upsidedown@downunder.com wrote in ><u3cd58dg8egllr6lgbsa0en02rflm791jc@4ax.com>: > >>On Sun, 16 Sep 2012 18:45:35 GMT, Jan Panteltje >><pNaonStpealmtje@yahoo.com> wrote: >> >>>>>Probably signal to noise ratio, in fact bit error rate. >>>>>In GPS (the US system) all sats transmit at the same frequency, >>>>>their data xored with some pseudo random code that is different for =each sat.>>>> >>>>If you use a 4-quadrant (Gilbert cell) multiplier (mixer) instead of =a>>>>XOR gate, the despread signal will definitely have a positive SNR in >>>>the 1000/50 Hz bandwidth) and the absolute signal power should be >>>>easily measurable. >>> >>>No, you misunderstand the GPS system. >>>The satellites all transmit at the same frequency, their digital =signals are>>>xored before modulation with a pseudo random code, a so called 'Gold =code'.>>>This code is different for each satellite. >>>Basically this is done with a shift register. >>>In the receiver AFTER demodulation the digital signal is run through a=similar>>>shift register, and one by one tested for the correct Gold code (each =sat has its own code).>>>In case of noise, you do not get an exact match against the know =codes, and the number of wrong>>>bits is then a measure for the signal to noise ratio. >>>100% good signal, no bit errors. >>>Weak signal lots of bit errors. >>> http://en.wikipedia.org/wiki/GPS_signals >> >>The GPS signal is an ordinary direct sequence spread spectrum (DSSS) >>signal. It can be received with a mixer/multiplier/xor gate by >>multiplying the received signal with the same chip clock (in this case >>1.023 MHz satellite specific PRN sequence) _synchronized_ with the >>transmitter modulator chip clock. After the demodulator the about 1 >>MHz wide spread spectrum signal is despread to something about 1 kHz. >>At this point you could also make power measurements. After this, the >>50 bit/s data signal is extracted. >> >>The shift register and bit error detection you are talking about has >>to do with signal acquisition _before_ the receiver chip clock >>generator has been synchronized with the transmitter chip clock. > >Partly, >as you want to display signal to noise for each individual satellite, >you have to identify the satellite in the signal. >For that to happen you need to detet its Gold code directly. >Now you are full circle :-)Not entirely. The empherides for all the satellites is in flash and can be updated by data from the satellites which are in turn updated by = ground support stations. Since a time solution is relatively in dependant of = the location solution and the satellites found, it can be use to get the empherides data and thus know which satellites to look for the location solution. Of course the receiver remembers the last location it had lock and keeps time while powered off, the empherides is immediately useful in most cases. ?-)
Reply by ●September 20, 20122012-09-20
On Mon, 17 Sep 2012 23:42:23 +0300, upsidedown@downunder.com wrote:>On Mon, 17 Sep 2012 08:01:03 GMT, Jan Panteltje ><pNaonStpealmtje@yahoo.com> wrote: > >>On a sunny day (Mon, 17 Sep 2012 08:30:48 +0300) it happened >>upsidedown@downunder.com wrote in >><u3cd58dg8egllr6lgbsa0en02rflm791jc@4ax.com>: >> >>>On Sun, 16 Sep 2012 18:45:35 GMT, Jan Panteltje >>><pNaonStpealmtje@yahoo.com> wrote: >>> >>>>>>Probably signal to noise ratio, in fact bit error rate. >>>>>>In GPS (the US system) all sats transmit at the same frequency, >>>>>>their data xored with some pseudo random code that is different for=each sat.>>>>> >>>>>If you use a 4-quadrant (Gilbert cell) multiplier (mixer) instead of=a>>>>>XOR gate, the despread signal will definitely have a positive SNR in >>>>>the 1000/50 Hz bandwidth) and the absolute signal power should be >>>>>easily measurable. >>>> >>>>No, you misunderstand the GPS system. >>>>The satellites all transmit at the same frequency, their digital =signals are>>>>xored before modulation with a pseudo random code, a so called 'Gold =code'.>>>>This code is different for each satellite. >>>>Basically this is done with a shift register. >>>>In the receiver AFTER demodulation the digital signal is run through =a similar>>>>shift register, and one by one tested for the correct Gold code (each=sat has its own code).>>>>In case of noise, you do not get an exact match against the know =codes, and the number of wrong>>>>bits is then a measure for the signal to noise ratio. >>>>100% good signal, no bit errors. >>>>Weak signal lots of bit errors. >>>> http://en.wikipedia.org/wiki/GPS_signals >>> >>>The GPS signal is an ordinary direct sequence spread spectrum (DSSS) >>>signal. It can be received with a mixer/multiplier/xor gate by >>>multiplying the received signal with the same chip clock (in this case >>>1.023 MHz satellite specific PRN sequence) _synchronized_ with the >>>transmitter modulator chip clock. After the demodulator the about 1 >>>MHz wide spread spectrum signal is despread to something about 1 kHz. >>>At this point you could also make power measurements. After this, the >>>50 bit/s data signal is extracted. >>> >>>The shift register and bit error detection you are talking about has >>>to do with signal acquisition _before_ the receiver chip clock >>>generator has been synchronized with the transmitter chip clock. >> >>Partly, >>as you want to display signal to noise for each individual satellite, >>you have to identify the satellite in the signal. >>For that to happen you need to detet its Gold code directly. >>Now you are full circle :-) > >So in reality, you need four independent signal strength signals for >the best (geometry) four satellites=46our satellites is minimum for a 3d solution, precision increases dramatically with 6 or more satellites in view. Today having 10 satellites in view is normal out in flat country terrain. Cities and mountains not so much. ?-)
Reply by ●September 21, 20122012-09-21
On Thu, 20 Sep 2012 19:59:36 -0700, josephkk <joseph_barrett@sbcglobal.net> wrote:>On Mon, 17 Sep 2012 23:42:23 +0300, upsidedown@downunder.com wrote: > >>On Mon, 17 Sep 2012 08:01:03 GMT, Jan Panteltje >><pNaonStpealmtje@yahoo.com> wrote: >> >>>On a sunny day (Mon, 17 Sep 2012 08:30:48 +0300) it happened >>>upsidedown@downunder.com wrote in >>><u3cd58dg8egllr6lgbsa0en02rflm791jc@4ax.com>: >>> >>>>On Sun, 16 Sep 2012 18:45:35 GMT, Jan Panteltje >>>><pNaonStpealmtje@yahoo.com> wrote: >>>> >>>>>>>Probably signal to noise ratio, in fact bit error rate. >>>>>>>In GPS (the US system) all sats transmit at the same frequency, >>>>>>>their data xored with some pseudo random code that is different for each sat. >>>>>> >>>>>>If you use a 4-quadrant (Gilbert cell) multiplier (mixer) instead of a >>>>>>XOR gate, the despread signal will definitely have a positive SNR in >>>>>>the 1000/50 Hz bandwidth) and the absolute signal power should be >>>>>>easily measurable. >>>>> >>>>>No, you misunderstand the GPS system. >>>>>The satellites all transmit at the same frequency, their digital signals are >>>>>xored before modulation with a pseudo random code, a so called 'Gold code'. >>>>>This code is different for each satellite. >>>>>Basically this is done with a shift register. >>>>>In the receiver AFTER demodulation the digital signal is run through a similar >>>>>shift register, and one by one tested for the correct Gold code (each sat has its own code). >>>>>In case of noise, you do not get an exact match against the know codes, and the number of wrong >>>>>bits is then a measure for the signal to noise ratio. >>>>>100% good signal, no bit errors. >>>>>Weak signal lots of bit errors. >>>>> http://en.wikipedia.org/wiki/GPS_signals >>>> >>>>The GPS signal is an ordinary direct sequence spread spectrum (DSSS) >>>>signal. It can be received with a mixer/multiplier/xor gate by >>>>multiplying the received signal with the same chip clock (in this case >>>>1.023 MHz satellite specific PRN sequence) _synchronized_ with the >>>>transmitter modulator chip clock. After the demodulator the about 1 >>>>MHz wide spread spectrum signal is despread to something about 1 kHz. >>>>At this point you could also make power measurements. After this, the >>>>50 bit/s data signal is extracted. >>>> >>>>The shift register and bit error detection you are talking about has >>>>to do with signal acquisition _before_ the receiver chip clock >>>>generator has been synchronized with the transmitter chip clock. >>> >>>Partly, >>>as you want to display signal to noise for each individual satellite, >>>you have to identify the satellite in the signal. >>>For that to happen you need to detet its Gold code directly. >>>Now you are full circle :-) >> >>So in reality, you need four independent signal strength signals for >>the best (geometry) four satellites > >Four satellites is minimum for a 3d solution, precision increases >dramatically with 6 or more satellites in view. Today having 10 >satellites in view is normal out in flat country terrain. Cities and >mountains not so much.Adding GLONASS satellites to your constellation helps immensely. Several chip vendors are adding GLONASS for this reason.
