I dont know if you have come across this before, but ill let you all know just in case
My original email to Garmin:
So having finally caved in and bought a Satnav ive observed something weird. If you power satnav up and hold the satellite signal strength icon for 5 seconds you get a screen that shows a sky map of what satellites can be seen and the signal strength of each satellite. Obviously the more and stronger the signals the better the accuracy of the satnav. In the car also have a dashcam and a phone charger plugged into the rear seat 12v power socket. The Satnav is plugged into the front 12v power socket And thats the problem. no matter what combination of power sources USB converter plugs and chargers if you plug the SatNav into the power alone the satellite signal strength is superb. As soon as you plug any other device into the power by whatever combination or means the satellite signal strength on the SatNav plummets sometimes to the point where it loses signal altogether. Unplugging a device (the satnav or the dashcam or charger)restore signal Im totally perplexed as to why it should do this ive tried different leads different power converters different plugs and sockets. Every time the satellite signal drops off as soon as the second device is plugged in Any idea why and how you get round the problem?
Anyway, Garmin wrote back with some bollox about doing a software and fiirmware upgrade, and a master reset, whic i didnt think for one minute woudl solve the problem, since it worked fine on its own.
Eventually, i cracked it and wrote back
Actually by judicious playing about with the problem ve cracked it , you might want to know the solution for other people.
The problem lay not in the satnav, but in the dashcam situated underneath.
It would seem that the dashcam appears to put out some sort of short range (about 12 inches) RF interference pretty much on or a harmonic of the satnav signal frequency, 163Mhz. When close up, it must swamp out the weaker satellite signals, because you can see the bar graph dropping down to almost nothing. Take the dashcam away (more than two feet), bar graph goes back up to full power. Siting the dashcam on the other side of the windscreen solved the problem, its far enough for the emissions of the dashcam to be too weak to affect the satnav.
SO there you go. Dont site the dashcam under the satnav!!!!