GPS / Ham radio interference

[Jeff Snyder]

Last year, I got a different car (old: 95 Pontiac Bonneville; new: 99 Pontiac Bonneville)... About that time, I noticed that my DeLorme Earthmate was not holding onto satellites very well at all -- I'd completely lose GPS every now and then (not even 2D coverage)... At first, I thought it might have been a windshield issue -- I know some windshields in some cars actually have tiny specks of metal in them, which some have said interfere with GPS signals (makes sense to me). This issue SEEMED to get better when I moved the Earthmate near the side window (vs. the windshield). The intermediate nature of the problem, however, made me question whether it really was a windshield issue. However, when chasing on 3/20, I found another link. Whenever I key up on my ham radio (I was talking on 146.55 and .525), the GPS signal would degrade and I'd eventually completely lose the signal. As long as I kept the transmission less than 4-5 seconds in length, the GPS would just go down to 2D, before slowly getting back to 3D. Unfortunately, I even moved down to low power (5W from the radio -- Yaeusu FT-8900R, though with a mag-mount, trunk-mounted Comet SB-15 antenna, which is 5/8 wave on 2m w/ 4.15db gain) and still have the problem. I didn't use this radio very much before last year, so that might explain why I didn't notice the GPS interruptions before last year.

At any rate, has anyone else ever had this problem? I'm not really sure how to go about fixing this either... I can't roof-mount the antenna, since it's already on the big size for any mag-mount, so I really need to keep it on a short leash. I suppose I may be able to make a little metal box to put the GPS device in (not so much a box, obviously, but like a box with the top off, so the GPS has a clear view of the sky, but there would be metal wall between it and the ham antenna on the trunk). Ideas? Experiences?

IIRC, I think GPS runs about 1.5gHz, so I'm a little surprised that this is an issue.

 

[Tim Stoecklein]

If you're getting that much RF in the car, I'd worry more about other things than the GPS :blink:

I don't use the same GPS, mine is the eTrex, but I have never experienced the interference you mention. I'd be curious where the GPS is in relation to the radio itself. Have you checked that your not leaking RF somewhere inside the vehicle? I'm just grasping at straws...

 

[Jeff Snyder]

If you're getting that much RF in the car, I'd worry more about other things than the GPS :blink:

I don't use the same GPS, mine is the eTrex, but I have never experienced the interference you mention. I'd be curious where the GPS is in relation to the radio itself. Have you checked that your not leaking RF somewhere inside the vehicle? I'm just grasping at straws... [/b]

Yeah, if only I had an electric field meter... The radio is near the dash (under the dash, actually), and the GPS is on my dash, as far forward as possible. I'll see what I can find...

 

[Bill Hamilton]

I don't know if it is related either but every since I installed my Ham radio in my car my Delorme GPS doesn't hold a signal near as well. This is without transmitting anything.
Same as yours Jeff, radio is under dash and GPS on lower passenger side windshield.
Radio is an ICOM V8000 with a 5/8 wave NMO mount antenna located at the trunk with fender bracket on drivers side.
Who knows if it is the problem but the GPS problem and HAM radio installation do coincide with each other.

 

[PeteMcConnell]

Last year, I got a different car (old: 95 Pontiac Bonneville; new: 99 Pontiac Bonneville)... About that time, I noticed that my DeLorme Earthmate was not holding onto satellites very well at all -- I'd completely lose GPS every now and then (not even 2D coverage)... At first, I thought it might have been a windshield issue -- I know some windshields in some cars actually have tiny specks of metal in them, which some have said interfere with GPS signals (makes sense to me). This issue SEEMED to get better when I moved the Earthmate near the side window (vs. the windshield). The intermediate nature of the problem, however, made me question whether it really was a windshield issue. However, when chasing on 3/20, I found another link. Whenever I key up on my ham radio (I was talking on 146.55 and .525), the GPS signal would degrade and I'd eventually completely lose the signal. As long as I kept the transmission less than 4-5 seconds in length, the GPS would just go down to 2D, before slowly getting back to 3D. Unfortunately, I even moved down to low power (5W from the radio -- Yaeusu FT-8900R, though with a mag-mount, trunk-mounted Comet SB-15 antenna, which is 5/8 wave on 2m w/ 4.15db gain) and still have the problem. I didn't use this radio very much before last year, so that might explain why I didn't notice the GPS interruptions before last year.

At any rate, has anyone else ever had this problem? I'm not really sure how to go about fixing this either... I can't roof-mount the antenna, since it's already on the big size for any mag-mount, so I really need to keep it on a short leash. I suppose I may be able to make a little metal box to put the GPS device in (not so much a box, obviously, but like a box with the top off, so the GPS has a clear view of the sky, but there would be metal wall between it and the ham antenna on the trunk). Ideas? Experiences?

IIRC, I think GPS runs about 1.5gHz, so I'm a little surprised that this is an issue.
[/b]

 

[Stan Olson]

I used to have problems with my old XM radio (Roady) receiver and Delorme Earthmate receiver. I never really noticed any issues with the ham rig interfering unless I was using higher power, then I'd see the green light go to yellow or red. I got rid of my Earthmate a few months back and went with a wireless bluetooth GPS. I haven't noticed any interference issues with it and my ham rig. I picked up the Holux GR-236 bluetooth GPS with the new SiRF-III chipset. (it's amazing!) Here's a review of it:

http://www.pocketgpsworld.com/gr236.php

I can get signals where I never used to get them before, even indoors. I just velcro it to the passenger side of the dash towards the floor when I'm in the car. Granted I also have a DC power cable and external GPS antenna hooked up to it for even greater signal strength. If your laptop has bluetooth or if you pick up a bluetooth dongle, go for one of these units.

Stan

 

[PeteMcConnell]

Jeff,

I run the same radio from Yaesu. My antenna is a quad band which is a trunk mount of sorts on a Dodge Caravan. My GPS is Holux. I usually keep the GPS antenna on the dash. I don't have any issues as of yet. Good luck figuring this out and good choice of radios.

Pete-KC2LVU

 

[Bill Hamilton]

Being that this topic reminded me of the issue I went out and mess with it some.
I did have the GPS on the lower passenger side of the windshield so I moved it about 6" toward the center and it picked up 3D off with 4-5 sats finding it. All this with the Ham radio on and transmitting off and on with no problem noted.
Jeff, I don't know what could be causing your issue but thank you for bringing the topic up so I could fix my issue.

 

[Tim Johnson]

I have not had any issues with the gps, but my temperature/compass/trip display on the truck goes nuts if TX on high power.

I'm no antenna expert, but I do believe the vehicle itself becomes sort of a ground plain when an antenna is mounted on it. If your antenna is mounted on the right rear, the TX signal will be stronger (directionally) to the front left of you car, and vis versa....left rear mount, front right signal is stronger.....mounted on the roof, radiates more omni-directional etc. The location of the antenna could very well be having some impact in relation to the location of your GPS receiver. You could try moving one or both and do some tests to see how it reacts.


Might also be worth while inspecting the antenna cable to make sure you don't have any RF leaking inside the car as Tim suggested. Does the atenna's cable path run close to where the GPS or its cable is mounted? Its possible the shielding on the coax could be damaged where it connects to the radio, or runs out of a window or door or something? This would likely allow RF to travel up and down the outside of the coax. If nothing is obvious, perhaps a friend with a mag mount would let you borrow theirs and see if that reacts any differently. Just some thoughts.

Would certainly be interested in eventually hearing how you resolve it.

 

[Jeff Snyder]

Thanks for input so far! I just tested the setup with an SWR meter, and everything came up in the 1.1-1.4 range. I'd think that if there were issues with the coax or one of the connections that I'd find high or inconsistent SWR readings. FWIW, I'm running RG8 cable from the front of the car/cab into the trunk (and yes, the rather inflexible nature of RG8 made installation tricky LOL), where it connects to the RG58 coming from the NMO mag mount. :unsure: :huh:

 

[Tim Stoecklein]

One more thought Jeff.......I have heard of this happening more with HF than VHF, but what is the length of the wire from the GPS to the computer? You don't suppose it's close enough in wavelength that it's picking up the ham signal and running RF to the GPS receiver do you? I can't imagine that wire has much shielding to it at all. Try shielding the GPS wire more?

I used to be able to turn the lamp on and off in our bedroom when I was doing CW(morse code) on 40 meters :blink: RF can do strange things!

 

[KMcCallister]

Last year, I got a different car (old: 95 Pontiac Bonneville; new: 99 Pontiac Bonneville)... About that time, I noticed that my DeLorme Earthmate was not holding onto satellites very well at all -- I'd completely lose GPS every now and then (not even 2D coverage)... At first, I thought it might have been a windshield issue -- I know some windshields in some cars actually have tiny specks of metal in them, which some have said interfere with GPS signals (makes sense to me). This issue SEEMED to get better when I moved the Earthmate near the side window (vs. the windshield). The intermediate nature of the problem, however, made me question whether it really was a windshield issue. However, when chasing on 3/20, I found another link. Whenever I key up on my ham radio (I was talking on 146.55 and .525), the GPS signal would degrade and I'd eventually completely lose the signal. As long as I kept the transmission less than 4-5 seconds in length, the GPS would just go down to 2D, before slowly getting back to 3D. Unfortunately, I even moved down to low power (5W from the radio -- Yaeusu FT-8900R, though with a mag-mount, trunk-mounted Comet SB-15 antenna, which is 5/8 wave on 2m w/ 4.15db gain) and still have the problem. I didn't use this radio very much before last year, so that might explain why I didn't notice the GPS interruptions before last year.

At any rate, has anyone else ever had this problem? I'm not really sure how to go about fixing this either... I can't roof-mount the antenna, since it's already on the big size for any mag-mount, so I really need to keep it on a short leash. I suppose I may be able to make a little metal box to put the GPS device in (not so much a box, obviously, but like a box with the top off, so the GPS has a clear view of the sky, but there would be metal wall between it and the ham antenna on the trunk). Ideas? Experiences?

IIRC, I think GPS runs about 1.5gHz, so I'm a little surprised that this is an issue.
[/b]

Jeff, I also have experienced the same problem with my Earthmate GPS since changing cars a couple years ago. While it gets a good signal under ideal conditions (ie, not chasing), the signal through the windshield does not work as well as it did previously. I tried it in the back window which seemed to work better. But, that places the little yellow box at most about 4 feet from my 2m/440 anteanna and it loses its fix everytime I key up at 50W. At 5W and 10W, no obvious problem. As I'm not willing to throw away the 50W, I've had to put up with degraded performance of the GPS in the front window.

Experiences, yes. Ideas, no.

 

[J West]

I'm having the same problem with SA '06 and the LT20 receiver, and my primary installation is sans radio at this point. It loses 3D lock and goes into 2D or fails completely and has to re-aquire the birds. This happens in our Explorer and my old Chevy, neither of which have any type of solarized windshield.

I am assuming it's the LT-20, since I've never seen this poor of a performance from GPS units. Could it be a poor receiver? I'm thinking about an external amplified antenna at this point.

 

[Tony Laubach]

I can jump on board with Jeff's issue as I experienced the similar problem in my chasing trip Thursday. I didn't take the time to fidget with settings, so I'm not sure if the power output I was on made a difference, however, I did find less interference when I moved the puck towards the driver's side of the van where my rig is mounted below the glove box on the passenger side. While it didn't competely eliminate the issue, it seemed to take longer for the signal to completely drop away.

 

[Jeff Snyder]

I can jump on board with Jeff's issue as I experienced the similar problem in my chasing trip Thursday. I didn't take the time to fidget with settings, so I'm not sure if the power output I was on made a difference, however, I did find less interference when I moved the puck towards the driver's side of the van where my rig is mounted below the glove box on the passenger side. While it didn't competely eliminate the issue, it seemed to take longer for the signal to completely drop away. [/b]

I may just put away the Earthmate and, if I can find my serial-to-usb adapter, just use my older GPS unit (Garmin 12MAP handheld unit). For whatever reason, this GPS never lost any connection when I used the ham, despite Earthmate consistently losing the signal. :huh: