GPS 'drop out'
Thread Starter
Join Date: Aug 2003
Location: Not a million miles from EGTF
Age: 68
Posts: 1,579
Likes: 0
Received 0 Likes
on
0 Posts
GPS 'drop out'
Yesterday I had a long flight to East Anglia in the morning and my Skymap IIIC worked perfectly.
On the return later in the afternoon I had no GPS fix throughout the whole of the return flight.
I thought perhaps it was my installation but the companion aircraft had no reception on their Garmin handheld either. The only difference was that the return leg was flown 1000' lower then the outbound trip.
Can any of the PPRUNE experts give a view as to what causes this sort of problem. I know that having a properly installed fixed aerial is best but it isn't an option for me at the moment.
On the return later in the afternoon I had no GPS fix throughout the whole of the return flight.
I thought perhaps it was my installation but the companion aircraft had no reception on their Garmin handheld either. The only difference was that the return leg was flown 1000' lower then the outbound trip.
Can any of the PPRUNE experts give a view as to what causes this sort of problem. I know that having a properly installed fixed aerial is best but it isn't an option for me at the moment.
Join Date: Aug 2000
Location: S Warwickshire
Posts: 1,214
Likes: 0
Received 0 Likes
on
0 Posts
Handheld GPS units can be vulnerable to saturation from other radio transmitters. I used to occasionally get that in the vicinity of the old Rugby/Daventry masts.
Using an installed ariel that only has a view upwards, completely cured the problem as it was shielded from most ground based sources.
I think the RF rejection is better on some of the newer units.
Another possibility is the illegal use of low power GPS jammers by commercial drivers so that they can't be remotely tracked by their employers. They don't have much range, but may be a possibility.
Using an installed ariel that only has a view upwards, completely cured the problem as it was shielded from most ground based sources.
I think the RF rejection is better on some of the newer units.
Another possibility is the illegal use of low power GPS jammers by commercial drivers so that they can't be remotely tracked by their employers. They don't have much range, but may be a possibility.
Join Date: Apr 2008
Location: Near the end of a long, long road
Age: 76
Posts: 158
Likes: 0
Received 0 Likes
on
0 Posts
Two of us flew from Northamptonshire to Nottinghamshire yesterday, one of us with a Clarity and the other with a Garmin and no problem. Unlikely to be jamming then I would have thought.......
Did you try rebooting the unit? I've been told this can help.
Did you try rebooting the unit? I've been told this can help.
Moderator
It happens form time to time. Flying back across Sasketchewan last April in the 182, I flew for 1.4 hours with none of three GPS's (one VFR panel monuted, and two Garmin handhelds) able to get a fix. I could have really used the nav there, as it is rather featureless, and I was too low to receive a VOR in a meaninful way, for most of the trip!
Every now and again, the GPS system does not work for a while. It's still the best thing ever though!
Every now and again, the GPS system does not work for a while. It's still the best thing ever though!
Join Date: Oct 2008
Location: Surrey UK/Quebec CA
Posts: 148
Likes: 0
Received 0 Likes
on
0 Posts
It will happen on various occasions, especially with the handhelds. Most of them only have a small reciever, which even if you put on top of the panel you only have a small portion of the sky available to receive.
There could be all 24 satellites running, of which 18 are over the horizon, leaving 6 covering where you are flying. Presume your reciever wont pick up the 2 sats that are below 15 degrees elevation and the two behind you are blocked by your own aircraft... That leaves two, which is not sufficient to get a position.
Normally in the UK we have between 4-10 satellites available to use with GPS.
Rather than a GPS outage, you will probably find you might of had signal if you turned round and flew back the other way
There could be all 24 satellites running, of which 18 are over the horizon, leaving 6 covering where you are flying. Presume your reciever wont pick up the 2 sats that are below 15 degrees elevation and the two behind you are blocked by your own aircraft... That leaves two, which is not sufficient to get a position.
Normally in the UK we have between 4-10 satellites available to use with GPS.
Rather than a GPS outage, you will probably find you might of had signal if you turned round and flew back the other way
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
I suspect that if both units lose reception concurrently then it may be interference.
In many planes, with less than properly done RF cabling and old radios, doing a VHF transmission on the 11th or 13th subharmonic of 1575MHz (e.g. 121.15MHz) will wipe out GPS reception in seconds.
It is only when approving an IFR GPS installation for flying GPS approaches, or for BRNAV, that these tests are specified.
Anyway, here is the perfect solution to all GPS dropouts - you sack the relevant official
In many planes, with less than properly done RF cabling and old radios, doing a VHF transmission on the 11th or 13th subharmonic of 1575MHz (e.g. 121.15MHz) will wipe out GPS reception in seconds.
It is only when approving an IFR GPS installation for flying GPS approaches, or for BRNAV, that these tests are specified.
Anyway, here is the perfect solution to all GPS dropouts - you sack the relevant official
Join Date: Nov 2010
Location: London
Age: 54
Posts: 232
Likes: 0
Received 0 Likes
on
0 Posts
Another possibility....sometimes there is a glitch in the clock timing. As most GPS units actually never do a full reboot, but stay in warm standby, they assume their clock is nearly in sync with the satellites, and then fail miserably to get a signal if they are out of sync.
This has happened regualrly to me on marine GPS units from Garmin and others (lowrance was one, i think).
Powering off and on never seemed to make a difference.
I spoke to some technical suppotr guys at garmin, who gave me the forced resync process for the units. This takes a good 5+minutes to resync properly, and they tell me that after that, you really need to make sure the unit is on for a minimum of an hour to make sure it caches the correct time and movement for the satellites in view (which it then can extrapolate the others from).
This all sounded somewhat dubious to me, but i have to admit, ever since then, if I have lost a signal, a hard reboot has got things back working within a few minutes.
The shame is that for all the units I use (handheld, pocket, marine) the reboot method is different, and seems to be so on every type, even within the garmin range.
Ah well, still love GPS, and thankfully have never lost both GPS at the same time :-)
This has happened regualrly to me on marine GPS units from Garmin and others (lowrance was one, i think).
Powering off and on never seemed to make a difference.
I spoke to some technical suppotr guys at garmin, who gave me the forced resync process for the units. This takes a good 5+minutes to resync properly, and they tell me that after that, you really need to make sure the unit is on for a minimum of an hour to make sure it caches the correct time and movement for the satellites in view (which it then can extrapolate the others from).
This all sounded somewhat dubious to me, but i have to admit, ever since then, if I have lost a signal, a hard reboot has got things back working within a few minutes.
The shame is that for all the units I use (handheld, pocket, marine) the reboot method is different, and seems to be so on every type, even within the garmin range.
Ah well, still love GPS, and thankfully have never lost both GPS at the same time :-)
Join Date: Jul 2005
Location: SoCal
Posts: 1,929
Likes: 0
Received 0 Likes
on
0 Posts
You can get an external antenna for the Garmins at Maplins for a few quid. Has - for me - cured all reception problems, and that includes flying in remote parts of Africa and Australia.
Join Date: May 2001
Posts: 2,118
Likes: 0
Received 0 Likes
on
0 Posts
You can get an external antenna for the Garmins at Maplins for a few quid. Has - for me - cured all reception problems, and that includes flying in remote parts of Africa and Australia.
Join Date: May 2001
Location: 75N 16E
Age: 54
Posts: 4,729
Likes: 0
Received 0 Likes
on
0 Posts
Our G496 will freeze pretty much every time we pass the Rampisham HIRTA < 3000' < 5 miles (BBC world service). The screen locks up and the only way to restore it is to remove the battery to reset it. Took us ages to figure out what caused these lock ups and it was only when we noticed they were happening in the same place that we figured it out.
This is using a hull mounted antenna as well as aircraft power.
This is using a hull mounted antenna as well as aircraft power.
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
My KFC225 autopilot pitch servo burns out every time I fly over a certain spot just N of Le Mans in France
Lat 48.15129 degrees N
Long 0.28158 degrees E
I have GPS data to prove it from two occassions (1 year apart) and there was a 3rd failure some years before that. The French military (contacted via Socata) deny they have anything there but clearly it is a surface radiator of some sort and most likely a tracking (missile) radar which does the "job" for a number of seconds, exposing a design defect in the servo (a current limit sircuit which self destructs the servo when activated
).
However the only occassions I have lost GPS were in 2004 in the middle of the Adriatic, about abeam Split I think, and both units I had went wild for about a minute or two, and another was departing from Padova Italy in 2006 when the KLN94 would not pick up the sats, so I proceeded while telling ATC I had no RNAV capability and flew VOR routings (and used the backup GPS) for about an hour until the thing woke up. The former occassion was clearly interference, and the latter one was probably a loss of ephemeris data on the GPS module inside the KLN94.
In the consumer world there are loads of crap GPSs which only just hang in there - smartphones, PDAs, the Ipad, the old Sirf-2 units with their 200ft altitude error, etc.
Lat 48.15129 degrees N
Long 0.28158 degrees E
I have GPS data to prove it from two occassions (1 year apart) and there was a 3rd failure some years before that. The French military (contacted via Socata) deny they have anything there but clearly it is a surface radiator of some sort and most likely a tracking (missile) radar which does the "job" for a number of seconds, exposing a design defect in the servo (a current limit sircuit which self destructs the servo when activated
).However the only occassions I have lost GPS were in 2004 in the middle of the Adriatic, about abeam Split I think, and both units I had went wild for about a minute or two, and another was departing from Padova Italy in 2006 when the KLN94 would not pick up the sats, so I proceeded while telling ATC I had no RNAV capability and flew VOR routings (and used the backup GPS) for about an hour until the thing woke up. The former occassion was clearly interference, and the latter one was probably a loss of ephemeris data on the GPS module inside the KLN94.
In the consumer world there are loads of crap GPSs which only just hang in there - smartphones, PDAs, the Ipad, the old Sirf-2 units with their 200ft altitude error, etc.
Join Date: Nov 2010
Location: London
Age: 54
Posts: 232
Likes: 0
Received 0 Likes
on
0 Posts
Slightly off topic, but we did this cracking experiment when I was at college. Get a lightbulb, solder two tuned lengths of wire to it to act as an aerial, cut to the correct length for a local transmitter frequency. Drive up to the transmitter, and see when the bulb lights up....then carry on driving closer and see how close you can get before it burns out. Then do the math....if it can burn out a 25W bulb at this distance, and it has a roughly donut shaped transmission pattern, and it reduces by the 3rd power with distance, how much power is it transmitting?
(and how quickly should you get "outta there" before you have no skin left!!!)
We did something similar with "shielded" wire, just to see how effective shielding was, both inside equipment and from external receivers to equipment....result....most shielded cable is lower quality than it should be....and delicate electronic kit will go phutz just from the current induced in the grounding shield, forget about the signal wire!
(and how quickly should you get "outta there" before you have no skin left!!!)
We did something similar with "shielded" wire, just to see how effective shielding was, both inside equipment and from external receivers to equipment....result....most shielded cable is lower quality than it should be....and delicate electronic kit will go phutz just from the current induced in the grounding shield, forget about the signal wire!
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
Yes - I used to be a radio ham in the 1960s (OK1OFA) and we could light up a small (very small, not 25W) bulb from a 80m shortware aerial strung between two blocks of flats.
That was just picking up the mix of normal distant broadcasts, mostly from outside the country; stuff like the BBC World Service
Near a transmitter I can imagine you would get a lot more power.
But at the same time there is no known effect on biology from radio frequencies, apart from the heating effect on tissues (the old mobile phone safety debate).
This is why GPS installations need to be done properly, with a rooftop aerial, RG400 cable, etc. GPS has a great property that if it fails it is normally really obvious (unlike navaids which can do all kinds of funny stuff) but it is of no help to the pilot if it stops working.
That was just picking up the mix of normal distant broadcasts, mostly from outside the country; stuff like the BBC World Service
Near a transmitter I can imagine you would get a lot more power.
But at the same time there is no known effect on biology from radio frequencies, apart from the heating effect on tissues (the old mobile phone safety debate).
This is why GPS installations need to be done properly, with a rooftop aerial, RG400 cable, etc. GPS has a great property that if it fails it is normally really obvious (unlike navaids which can do all kinds of funny stuff) but it is of no help to the pilot if it stops working.
Join Date: Jul 2005
Location: SoCal
Posts: 1,929
Likes: 0
Received 0 Likes
on
0 Posts
Is this a pukka installation or a DIY job? (Genuine question)
). You stick it low on the windshield, so it looks as much skywards as possible, thereby eliminating the shielding of the airframe. Comes with a 5-foot or so cable. Long enough to position the GPS unit anywhere in the cockpit (mine lives on a yoke mount).
I've had perfect reception with this setup even in parts of the world where only a handful of satellites are visible and the unit could only barely 'lock on' without the antenna.
One caveat though - this antenna is 'active', meaning it draws power. If you run your handheld off batteries, have spares to hand!
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
I think all modern GPS antennae are "active" i.e. they have a built in amplifier. It draws about 30mA at 5V, IIRC.
There are a few passive ones around but the only one I have used is an Iridium/Thuraya satphone one which also has a GPS bit built-in - all passive. You can get one of these installed on your plane, to get weather data when airborne, or (with a load more wiring) even get voice comms so you can phone people up and pose No standalone GPS I know of uses the passive GPS antenna part; it is purely for the GPS requirement of the satellite phones.
There are a few passive ones around but the only one I have used is an Iridium/Thuraya satphone one which also has a GPS bit built-in - all passive. You can get one of these installed on your plane, to get weather data when airborne, or (with a load more wiring) even get voice comms so you can phone people up and pose
No standalone GPS I know of uses the passive GPS antenna part; it is purely for the GPS requirement of the satellite phones.
Join Date: Nov 2010
Location: London
Age: 54
Posts: 232
Likes: 0
Received 0 Likes
on
0 Posts
IO, gotta say, at one point I was working for BT in their development labs, and if you saw the number of pidgeons we had to clear out the microwave transmitter horns, I'm not sure you'd think it was quite so benign :-)
As you say, its the heating effect that causes it, but when your goose is cooked, oh boy is it cooked!
We did some similar experiments with fluorescent tubes under HT power lines. Just the induced current in the tube cap is enough to light the whole thing up. And as for lightening storms....well, lets just say I don't go out and hold fluorescent tubes up in storms any more :-)
As you say, its the heating effect that causes it, but when your goose is cooked, oh boy is it cooked!
We did some similar experiments with fluorescent tubes under HT power lines. Just the induced current in the tube cap is enough to light the whole thing up. And as for lightening storms....well, lets just say I don't go out and hold fluorescent tubes up in storms any more :-)
