[TriEmbed] GPS/RF issue

[Kevin McClaning]

I've had this exact problem. The SNR of GPS is very low and anything 
will interfere with it. In my case, I had a power amplifier (PA) on the 
same antenna mast as my GPS antenna. Both were filtered to their 
respective bands. Because of other system parameters, I couldn't power 
the PA off so I simply terminated its input into a matched load when I 
wasn't using it. The noise generated by the terminated PA put enough 
noise in the GPS band to block it, despite the filters. I ended up 
connecting the PA's output to its antenna through an RF switch. When I 
wasn't using the PA, I terminated both the Tx antenna and the output of 
the PA.

So, filter the input of the GPS antenna, if you can. Buy a GPS that's in 
a metal box. If you're transmitting, even far way from the GPS band, see 
the above paragraph. Power down anything you don't need when you're not 
using it. Maybe ignore the output of the GPS while you're using  bits of 
your system that you've seen interfere with the GPS..

Physical isolation (e.g. wrapping things in aluminum foild) is hard to 
do repeatably and reliably. Antenna separation is definitely your friend.

Kevin

On 4/30/2019 10:33 AM, Charles West via TriEmbed wrote:
> Hello from the North!
>
> I'm still working on the golf course robot.  Recently I've run into a 
> rather odd issue.  When I put everything together for my 1/8 scale RC 
> car platform, my GPS module refused to converge.  I spent a solid 4 
> days debugging it only to eventually discover that the problem 
> appeared to be that my USB 3 camera was putting out large amounts of 
> RF interference of a spectrum suitable to interfere with my GPS even 
> when there was a metal ground plane between the GPS and the rest of 
> the equipment.
>
> Eventually, a combination of wrapping the camera in metal tape, 
> placing the GPS with a ground plane elevated way above the rest of the 
> robot and wrapping the camera's cable in aluminum foil finally got the 
> GPS to converge.  The only problem is, the accuracy of the GPS is far 
> worse than in the previous version of the robot.  Originally, I got 
> within a 2-3 meters with an occasional drift.  Now it squiggles all 
> over the place.
>
> Does anyone know what I should try next to get decent performance 
> and/or hunt down any interference for the GPS?
>
> Thanks,
> Charlie West