View Full Version : Electrical Interference

20th March 2006, 07:48 PM
Gidday all. I've got a cheap GPS receiver that seems to be getting interference from the wiring loom when I wire it through the fire wall of my car. When I switch on the moving map on my laptop everything works well but after driving for a minute or two the moving map freezes. I thought I might have had a configuration problem so I had a play with that, threw it all back in the car and everything worked fine. So, I decided to wire it back through the fire wall thinking that everything would be alright only to find that the moving map froze again after a minute or two. I can only presume that the wiring loom is interfering with the GPS receiver. Has anyone else experienced this?

20th March 2006, 08:11 PM
Without knowing what 'cheap' GPS and what moving map software......I'm assuming a mouse GPS and Ozi???............I'll have a go!

Have you tried to watch the NMEA output using any kind of app that can do this?

Ozi has the option to view the NMEA output, and there are a number of app thatcan monitor GPS output with nice blinking lights and all kinds of bells and whistles....my fave is VisualGPS (http://www.visualgps.net/) :)

I'm currently logging the output of my GPS, it's only using 1.7Meg of RAM... handy when on an old laptop...etc, and shows me the NMEA data as it comes in, as well as all the other GPS data on a big screen.

That's just one of many apps available....but th epoint is to see 'what is going on with the connection.
Is it going........ $GPGLL,3743.4548,S,14457.2848,E,010558.481,A*26... ....etc

OR !@#553(*&^%~`'":>?<}|||(*&7889OI/*-???>/<(*&


Is there any other way to route the cable?

Have you tried to wrap the cable with some foil only around the immediate area near the firewall/wiring loom and wrap some plastic sheathing (spirally wire protector, easliy available from all auto shops.
A bit of cheap shielding protection....it may not work but it can't hurt either!

An old bloke, electrician, showed me this 'trick' about 20 years ago when I started my youth as a 'DOOF DOOF' type, but all I hard was zzzzzDOOFzzzzz from the AM/FM stereo cassette radio I just installed!! :D )

20th March 2006, 08:19 PM
Woops, sorry I should have said that the GPS receiver is a TWIG and I am using Ozi. Yes, I have re-routed the cable away from any wires and all works well but as soon as I put it through a rubber gromit in the fire wall I have the trouble. I have thought about foil or thick insulation, but haven't tried it. I might have to give it a go. It's not a huge problem, I was just curious if anyone else has had interference issues.

20th March 2006, 08:40 PM
It most definitely is some kind of interference...but, me being the curious type, I'd try to find out what's going on!

At least if there is data coming through at all or if the interference is making it all garbled?

In Ozi (while the GPS is connected, and supposedly sending data), on the Toolbar go to 'Moving Map' and choose 'Show NMEA Input and Output'

This will pop up the window that show NMEA data, and you can log to a file, and post a small snippet and someone with more intelligence can decipher the data...etc.

Can you slow down the COMS baud rate? (is the TWIG configurable?)
Slower baud rate is better in high interference environment.....

Oh! I forgot..I've seen foil wrapped cable sheath (kinda expensive!) used for racing and show off purposes...may be an idea!


Les Addison
21st March 2006, 09:40 AM
When you install HF radio , you dont run 12v feed cables next to automatic antenna cables as this gives you interferance problems, common to Barrett & Codan . Also a very troublesome little critter, is the mighty Megapulse,that lots of 4bs use these days. Very bad on AM radio ,and tx& rx on HF..Les