Re: External GPS antenna question
On Friday 03 July 2009 22:42:04 Mikhail Umorin wrote: > Hello -- > Thank you all for the feedback! I have decided to get a passive antenna (Arcon: GPS-ANT-MMCX, from Amazon.com) for just a good reception and more accurate fix in the open. And for car/indoor/rainforest situations I shall get a retransmitting antenna like at http://pc-mobile.net/gpsant.htm when I really need it. This way I shall not be draining the battery to amplify the signal like with an active antenna. Mikhail. ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
BTW, anyone have any info on the radiation pattern of the internal antenna? Rúben Em Seg, Julho 6, 2009 13:31, Helge Hafting escreveu: > Tomasz Suchan wrote: >> Hi Armin, >> >>> I use the atenna for GPS Tracking during biking and car tours. >>> As the FR is always running (no sleep) and with activated GPS >>> module - the battery last about 4h - then it's empty. >> >> Is accuracy much better with external antenna? > > If the external antenna can be placed in a better location than the > internal one - or if it gets better signal strength. > > An external antenna on the car roof may see more satellites than the > FR sitting on the dashboard, because that metal roof block radio > transmission. > > Now, the FR will see many satellites even inside a car, but those > signals cannot penetrate directly through the roof. Some satellites will > be seen directly through windows. Signals from the rest may bounce off > the hood and come in through windows, or diffract (bend) around the roof > edge. Such redirected signals are weaker, and they give greater position > error. The latter because they really give the position where your FR > would have been, _if_ the signal had not been diffracted or reflected. > > The GPS receiver is smart, and will discard data from satellites that > seem to disagree with the rest. But there are two problems with this: > * An extra satellite that gets discarded no longer helps improving >accuracy. > * If two groups of satellites seems to disagree on position, then the >receiver could lock onto the wrong group for a while. > > An external antenna see all the satellites directly, and > don't suffer such problems. Unless you are near tall buildings or > mountainsides, which cause the same kind of problems. > > > So an external antenna is great if you have a roof above you. > Such as in a car or boat. The problems above don't happen on a bike. > Still, an external antenna might help, it may be bigger/better than the > internal antenna and get more from a weak signal. For example, if you > move around in heavy rain in a forest. > > Helge Hafting > > > > ___ > Openmoko community mailing list > community@lists.openmoko.org > http://lists.openmoko.org/mailman/listinfo/community > -- Rúben Leote Mendes -- ru...@netureza.pt ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
Tomasz Suchan wrote: > Hi Armin, > >> I use the atenna for GPS Tracking during biking and car tours. >> As the FR is always running (no sleep) and with activated GPS >> module - the battery last about 4h - then it's empty. > > Is accuracy much better with external antenna? If the external antenna can be placed in a better location than the internal one - or if it gets better signal strength. An external antenna on the car roof may see more satellites than the FR sitting on the dashboard, because that metal roof block radio transmission. Now, the FR will see many satellites even inside a car, but those signals cannot penetrate directly through the roof. Some satellites will be seen directly through windows. Signals from the rest may bounce off the hood and come in through windows, or diffract (bend) around the roof edge. Such redirected signals are weaker, and they give greater position error. The latter because they really give the position where your FR would have been, _if_ the signal had not been diffracted or reflected. The GPS receiver is smart, and will discard data from satellites that seem to disagree with the rest. But there are two problems with this: * An extra satellite that gets discarded no longer helps improving accuracy. * If two groups of satellites seems to disagree on position, then the receiver could lock onto the wrong group for a while. An external antenna see all the satellites directly, and don't suffer such problems. Unless you are near tall buildings or mountainsides, which cause the same kind of problems. So an external antenna is great if you have a roof above you. Such as in a car or boat. The problems above don't happen on a bike. Still, an external antenna might help, it may be bigger/better than the internal antenna and get more from a weak signal. For example, if you move around in heavy rain in a forest. Helge Hafting ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
On Sat, Jul 04, 2009 at 09:17:25PM +0400, Paul Fertser wrote:
> Sebastian Krzyszkowiak writes:
> > On 7/4/09, Hammer Armin wrote:
> >> With the internal gps antenna, the first fix last quite long -
> >> with the external - within 5min to 10min I get a fix.
> >
> > WTF? I'm getting fix easly with *internal* GPS antenna in 30 seconds -
> > 2 minutes...
>
> Because you already have almanac (and sometimes ephemeris) data.
Where would I have it from (that Hammer Armin doesn't)?
I ran the GPS-TTFF script below standing on my balcony. Times with * are
with the --coldstart option.
45* 38 57 48 48 44 44* 45* 52* 44*
And that's on Debian, which doesn't have the latest-and-greatest FSO
where saving and restoring almanac and ephemeris works. Back when I briefly
used OM 2008.8, I also got a fix in around 45 s. I tried with the Freerunner
lying in the window frame, and then it took 11 minutes to get a fix. My
Freerunner is revision A6 with date code 20080722.
#!/bin/sh
# GPS-TTFF - Find GPS time to first fix using all the important buzz-words
# such as D-bus, Gypsy, freedesktop.org and freesmartphone.org.
# Destinations and paths are listed in /etc/dbus-1/system.d/*.
# Interfaces are "documented" at http://docs.freesmartphone.org/>.
DBUSCALL_='dbus-send --print-reply=undocumented --system --type=method_call
--dest='
if [ "--coldstart" = "$1" ]; then
rm -f /var/lib/freesmartphone/ogpsd.pickle
fi
# Crude way of stripping white-space from $() output.
GPSPOLICY=$(echo $(${DBUSCALL_}org.freesmartphone.ousaged
/org/freesmartphone/Usage org.freesmartphone.Usage.GetResourcePolicy
string:GPS))
${DBUSCALL_}org.freesmartphone.ousaged /org/freesmartphone/Usage
org.freesmartphone.Usage.SetResourcePolicy string:GPS string:enabled
START=$(date +%s)
# Where is the first return value from GetPosition documented?
while ${DBUSCALL_}org.freedesktop.Gypsy /org/freedesktop/Gypsy
org.freedesktop.Gypsy.Position.GetPosition \
| head -n 1 | grep -q -v -F -e 'int32 15' -e 'int32 7'; do
sleep 1
done
FINISH=$(date +%s)
echo "Time to first fix: $((${FINISH} - ${START})) s"
${DBUSCALL_}org.freedesktop.Gypsy /org/freedesktop/Gypsy
org.freedesktop.Gypsy.Position.GetPosition
${DBUSCALL_}org.freesmartphone.ousaged /org/freesmartphone/Usage
org.freesmartphone.Usage.SetResourcePolicy string:GPS string:${GPSPOLICY}
--
Rask Ingemann Lambertsen
Danish law requires addresses in e-mail to be logged and stored for a year
___
Openmoko community mailing list
community@lists.openmoko.org
http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
Al Johnson writes: >> 25 * 0.5 min = 12.5 min . I assume this gives a good estimate of TTFF >> >> If you already have almanac (which is the usual case as almanac is >> usually valid for months), you'll get a fix in a little more than 30 >> seconds (time required to receive ephemeris from visible sattelite). >> >> [1] http://gpsinformation.net/gpssignal.htm > > ~40s was a consistent lower limit from cold start TTFF tests made to test the > kernel SD drive strength and idle clock. IIRC this closely matches the cold > start TTFF specified for the Antaris 4. Thanks to Daniel i now know that Antaris 4 doesn't require almanac to start receiving ephemeris so yes, i see now how it can get FF in ~40s. Just tried it myself btw. Sorry for confusion. -- Be free, use free (http://www.gnu.org/philosophy/free-sw.html) software! mailto:fercer...@gmail.com ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
On Saturday 04 July 2009, Paul Fertser wrote: > Al Johnson writes: > > On Saturday 04 July 2009, Paul Fertser wrote: > >> Sebastian Krzyszkowiak writes: > >> > On 7/4/09, Hammer Armin wrote: > >> >> With the internal gps antenna, the first fix last quite long - > >> >> with the external - within 5min to 10min I get a fix. > >> > > >> > WTF? I'm getting fix easly with *internal* GPS antenna in 30 seconds - > >> > 2 minutes... > >> > >> Because you already have almanac (and sometimes ephemeris) data. > > > > With a good sky view and suitable constellation TTFF from cold is ~40s > > with the internal antenna, rootfs on SD and an early A05 without the > > capacitor on SD. For it to take >2min I need heavy urban canyoning, being > > indoors or in a vehicle, or an unusually poor constellation. > > Let me cite the site that looks to be authoritive enough [1]: [snip quote from link] > 25 * 0.5 min = 12.5 min . I assume this gives a good estimate of TTFF > > If you already have almanac (which is the usual case as almanac is > usually valid for months), you'll get a fix in a little more than 30 > seconds (time required to receive ephemeris from visible sattelite). > > [1] http://gpsinformation.net/gpssignal.htm ~40s was a consistent lower limit from cold start TTFF tests made to test the kernel SD drive strength and idle clock. IIRC this closely matches the cold start TTFF specified for the Antaris 4. Consensus at the time was that the GPS was powered down for long enough between tests that there would be a true cold start since the version we use has no nonvolatile storage for almanac and ephemeris. Assistance (ie providing almanac and ephemeris) is supposed to reduce TTFF to 10-20s, still significantly longer then a warm start. If you want to repeat the tests yourself the script and method are in the archives. ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
> and if you are carrying the FR in a pocket, yes it gets a lock most of > the time, but the track wobbles all over the place - up to a hundred > meters. And if driving through an "urban canyon", similar track errors > can occur. Ive wanted a small external powered antenna for some time to > improve this. I've noticed the same wobbles, but only when I'm not moving very quickly. Does anybody know if setting the GPS to "Pedestrian" instead of "Car" mode helps? Or is an antenna the only solution? --Ben ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
On Sat, 2009-07-04 at 19:56 +0100, Al Johnson wrote: > On Saturday 04 July 2009, Paul Fertser wrote: > > Sebastian Krzyszkowiak writes: > > > On 7/4/09, Hammer Armin wrote: > > >> With the internal gps antenna, the first fix last quite long - > > >> with the external - within 5min to 10min I get a fix. > > > > > > WTF? I'm getting fix easly with *internal* GPS antenna in 30 seconds - > > > 2 minutes... > > > > Because you already have almanac (and sometimes ephemeris) data. > > With a good sky view and suitable constellation TTFF from cold is ~40s with > the internal antenna, rootfs on SD and an early A05 without the capacitor on > SD. For it to take >2min I need heavy urban canyoning, being indoors or in a > vehicle, or an unusually poor constellation. > > Having almanac and ephemeris _should_ make it faster, as should > initialisation > with correct time and approximate location. Feed it incorrect data at startup > and you can get a very long TTFF, or no fix at all, and ogpsd has done this > at > some stages of its development. and if you are carrying the FR in a pocket, yes it gets a lock most of the time, but the track wobbles all over the place - up to a hundred meters. And if driving through an "urban canyon", similar track errors can occur. Ive wanted a small external powered antenna for some time to improve this. BillK ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
Al Johnson writes: > On Saturday 04 July 2009, Paul Fertser wrote: >> Sebastian Krzyszkowiak writes: >> > On 7/4/09, Hammer Armin wrote: >> >> With the internal gps antenna, the first fix last quite long - >> >> with the external - within 5min to 10min I get a fix. >> > >> > WTF? I'm getting fix easly with *internal* GPS antenna in 30 seconds - >> > 2 minutes... >> >> Because you already have almanac (and sometimes ephemeris) data. > > With a good sky view and suitable constellation TTFF from cold is ~40s with > the internal antenna, rootfs on SD and an early A05 without the capacitor on > SD. For it to take >2min I need heavy urban canyoning, being indoors or in a > vehicle, or an unusually poor constellation. Let me cite the site that looks to be authoritive enough [1]: "The navigation message is a continuous 50 bits/second data stream modulated onto the carrier signal of every satellite. It is a telemetry message, and the data is transmitted in logical units called frames. For GPS a frame is 1500 bits long, so takes 30 seconds to be transmitted. Every satellite begins to transmit a frame precisely on the minute and half minute, according to its own clock. Each frame is divided into five subframes, each 300 bits long. Subframes 1, 2 and 3 contain the high accuracy ephemeris and clock offset data. The "data content" (which I'll define later) of these three subframes is the same for a given satellite for consecutive frames for periods lasting as long as two hours. New subframe 1, 2 and 3 data sets usually begin to be transmitted precisely on the hour (see description of uploads and cutovers below). Subframe 1 contains second degree polynomial coefficients used to calculate the satellite clock offset. Subframes 2 and 3 contain orbital parameters. Subframes 4 and 5 are "subcommutated, which means that consecutive subframes have different "data content". This data does repeat, but 25 consecutive frames of subframe 4 and 5 data must be collected before the receiver has all of the unique "data content" being transmitted by the satellite. A satellite transmits the same "data content" in subframes 4 and 5 until it is next uploaded, or usually for about 24 hours. Subframes 4 and 5 contain the almanac data and some related health and configuration data." 25 * 0.5 min = 12.5 min . I assume this gives a good estimate of TTFF If you already have almanac (which is the usual case as almanac is usually valid for months), you'll get a fix in a little more than 30 seconds (time required to receive ephemeris from visible sattelite). [1] http://gpsinformation.net/gpssignal.htm -- Be free, use free (http://www.gnu.org/philosophy/free-sw.html) software! mailto:fercer...@gmail.com ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
On Saturday 04 July 2009, Paul Fertser wrote: > Sebastian Krzyszkowiak writes: > > On 7/4/09, Hammer Armin wrote: > >> With the internal gps antenna, the first fix last quite long - > >> with the external - within 5min to 10min I get a fix. > > > > WTF? I'm getting fix easly with *internal* GPS antenna in 30 seconds - > > 2 minutes... > > Because you already have almanac (and sometimes ephemeris) data. With a good sky view and suitable constellation TTFF from cold is ~40s with the internal antenna, rootfs on SD and an early A05 without the capacitor on SD. For it to take >2min I need heavy urban canyoning, being indoors or in a vehicle, or an unusually poor constellation. Having almanac and ephemeris _should_ make it faster, as should initialisation with correct time and approximate location. Feed it incorrect data at startup and you can get a very long TTFF, or no fix at all, and ogpsd has done this at some stages of its development. ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
Hi Tom > Is accuracy much better with external antenna? I usually have > something like +/- 3-5m accuracy and need something better. Hm. I only use the external antenna, but I think it's better than +/- 3-5m. When I import my gps infos into google-earth the waypoints follow quite accurate the bike-paths - which are no more than 1-2m wide. Or on the highway it shows the correct driving lane. Yours Armin ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
Sebastian Krzyszkowiak writes: > On 7/4/09, Hammer Armin wrote: >> With the internal gps antenna, the first fix last quite long - >> with the external - within 5min to 10min I get a fix. > > WTF? I'm getting fix easly with *internal* GPS antenna in 30 seconds - > 2 minutes... Because you already have almanac (and sometimes ephemeris) data. -- Be free, use free (http://www.gnu.org/philosophy/free-sw.html) software! mailto:fercer...@gmail.com ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
Hi Armin, > I use the atenna for GPS Tracking during biking and car tours. > As the FR is always running (no sleep) and with activated GPS > module - the battery last about 4h - then it's empty. Is accuracy much better with external antenna? I usually have something like +/- 3-5m accuracy and need something better. Regards, Tom ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
On 7/4/09, Hammer Armin wrote: > With the internal gps antenna, the first fix last quite long - > with the external - within 5min to 10min I get a fix. WTF? I'm getting fix easly with *internal* GPS antenna in 30 seconds - 2 minutes... ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: External GPS antenna question
Hi Mikhail, I use a HAMA GPS-ANTENNE MMCX with 2m cable on my FR. It is passiv one with a magnetic base. Just plug it in an start your gps-application. With the internal gps antenna, the first fix last quite long - with the external - within 5min to 10min I get a fix. > What are the implications of their use with FR (power consumption, > performance, etc)? I use the atenna for GPS Tracking during biking and car tours. As the FR is always running (no sleep) and with activated GPS module - the battery last about 4h - then it's empty. >Should" any antenna with MMCX connector work in FR? I don't know - I stick to the Wiki page and bought an Hama one. Yours Armin Mikhail Umorin wrote: > Hello -- > > I want to buy an external GPS antenna and would like to know what is the > difference between "active", passive (?), powered, and amplified antennas > (antennae). > > What are the implications of their use with FR (power consumption, > performance, etc)? > > Which ones of the above "should" work in FR? > > "Should" any antenna with MMCX connector work in FR? > > Thank you for your time, > > Mikhail. > > P.S. I checked http://wiki.openmoko.org/wiki/External_GPS_antennas but I want > to know more of the general info. > > ___ > Openmoko community mailing list > community@lists.openmoko.org > http://lists.openmoko.org/mailman/listinfo/community > > ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
