GPS Speedo signal

[32 Chevy]

I currently have an Autometer speedo in my roadster that utilises GPS. I am finding that on start up it can take anything from 1 to 10 minutes to pick up the satellite signal before the speedo will commence working. The sensor is mounted on the steering column and appears to have a clear line of sight to the heavens. I have spoken with autometer and they say the sensor has to be mounted flat and the cable from the sensor should be wound in about 150mm circle.
Does anyone utilise a similar set up and do you experience any similar problems?

Bill

[jailbar joe]

i have a speedhut gps speedo and it is usually takes about a minute at most to fire up....nothing special about the sensor or cabling....

we have one tunnel here in perth....quite funny going into the tunnel and watching the speedo needle just drop but comes back instantly on exiting
the tunnel

[Chrisso]

We have GPS systems i the Abrams M1A1 i used to instruct on in a previous life, it was nicknamed Blue force Tracker as the good guys appeared in blue and the bad guys in red, everything in red was considered enemy, my point being that it doesn't work inside a hangar as the transponder can't see/sense the satellite, hence blind. They over came this in the sandpit by using digital radio signal to transmit the same information, don't ask me how because I am not a boffin. But if you are starting off under cover it can take a fair while to "find" the satellite. I hope this helps.

[zedman8]

funny about that Joe the speed on my Garmin in the truck going thru the tunnel shows correct speed on exit it shows the truck going at 180 KMH goes crazy for about 30 secs then goes back to normal swear the bloody thing is female
mike

[Little Sport Coupe]

I have had a Speed Hut unit in my Model A Sort Coupe for about 8 years. The transponder sits on the dash rail next to the RH A pillar behind the windscreen. The instructions did specify to have the unit direct wired to avoid long delays when the ignition is first turned on.
I have had the same dropping out issue that Joe has had plus a couple of times when in tunnels the speedo needle has stayed at the speed it registered when I went into the tunnel and then read that as zero. When I emerged from the tunnel and it started reading again instead of 100kph the speedo showed 200kph. Had to turn of the ignition to reset the speedo. Fun in traffic.
Fitted a kill switch to the speedo so when this occurs I can just turn the speedo of and on again instead of the car.

Phill

[Newbee]

32 Chevy the GPS antenna ideally should be placed where it can get a 360 deg view of the sky, although this may be impractical in some situations. The GPS requires a minimum signal from at least 4 GPS satellites to calculate a position and speed but the more satellites it can see the more accurate it will be. Therefore antenna placement is quite important.

Lower accuracy (relatively compared to military and agricultural guidance systems) only use the L1 radio signal for calculation of location and speed so more satellites is better, where as higher accuracy systems also use L2 radio signal (that comes with additional costs in fees and more specialised GPS equipment) but the 2 bands effectively doubles the the number of satellites so 4 satellites becomes 8. That's why in car systems have an accuracy of around 5 m where as agricultural guidance is down to 2 cm and who knows how accurate military systems are but then again 2 cm is probably accurate enough for a guided missile

The radio signal from the GPS satellites is also not a strong signal so again antenna placement is important. Also bear in mind that there are only 31 satellites in the GPS constellation (US ones) to cover the entire globe so cover for us in the Southern Hemisphere can be limited as the constellation is designed to favour the Northern Hemisphere.

Parking in the shed for a couple of weeks in between runs will cause longer delays in acquiring a fix as the almanac that tells the GPS where to look for satellites needs to be refreshed.

The thing with winding the antenna cable is just about correct storage of excess cable and not kinking or damaging the cable in any way, it will not enhance or degrade the signal but keep it away form any sort of possible interference.

Regards Newbee

[32 Chevy]

Thanks to all for your input. For some unknown reason the speedo has suddenly decided to react within about 5 mins of start up which is tolerable. I wish I could say it was some masterful engineering change I made but sadly not. Maybe the US has launched a couple of more satellites or the system has just settled in after a few runs.

Again thanks
Bill