VHF interference from my Garmin 188

Stanley-J

While going through the Lake Champlain locks, I noticed I had a constant pulse of interference on VHF channel 13. I would have to turn off the GPS to hail the Lock Masters. My radio is about 10" from the Garmin chartplotter /GPS . I moved the radio about 3 feet away from the unit and basically had the same problem. The GPS antenna is located on top of the cabin roof about 1 foot from the VHF antenna . I also notice a few higher channels with the same pulse interference. Has anyone experience any radio interference from your GPS? With my radar on I have no problem which is where I initially though the pulse was coming from as the beam rotates but it was fine.

thataway · Posted: Thu Oct 05, 2006 9:38 am Post subject:

Was the interference only when in the locks or in the proximity of the locks?

There have been reports of GPS antennas and VHF interference. I have discussed some of this with Ben Elison (Panbo). It probably is related to less than adequate shielding--both on the GPS antenna, and the coax from the VHF.

I had this problem with a new Lowrance unit--both FF and hard drive chart plotter. Lowrance's response was to move the GPS antenna 6 feet from the VHF antenna, have no antenna wires run parallel to each other, use different wiring directly from the battery for the VHF and GPS. (I wonder what type of boats these folks use--hard to do this on a C Dory!). Plus in my case I have two VHF and two GPS antennas. So, I started putting ferrite beads on the various inputs and outputs--on the GPS on the power, the buss power (NMEA 2000) the depth finder and GPS antenna power. Then added beads to one of the VHF's power and antenna. This got rid of 80% of the interference. I suspect if I had re routed the GPS antennas, It would have gotten rid of the other 20%. Interestingly enough, I had a second Lowarance antenna, which I put 20 feet away, no run within 4 feet of the radios, and had no interference. I also have a Standard Horizon chart plotter--and it gives no interference. I think that some of the problem is in the shielding of the fish finder cable also. With copper wire costing more, I suspect that less is used in the shielding.

Hope that this gives a few clues of where to start.
73's

Fairbro · Posted: Thu Oct 05, 2006 10:27 am Post subject:

I have had similar interference on my hand held VHF that originated from my Humminbird depth finder, trip log, speedometer combo. Now that I think about it, I would stop to transmit because of noise level and then it would be fine. It was a constant "chuck, chuck, chuck sound on all channels. It is the reason I eventually went to a permanent mount radio with outside antenna. No more problem and the proximity of the antennas is close. Do you have any other accessories like a depth finder near by?

Stanley-J · Posted: Thu Oct 05, 2006 11:42 am Post subject:

Thanks Bob, Gary & Gerrie,
The interference was all the time even home in the driveway. The Garmin 188 is a chartplotter, GPS, fish finder,depth & speed indicator, etc. I even had the problem with my hand held when I stood in the back of the boat. Again it was only on 13, and I think 68. All the other channels were clear as a bell. Thinking about the wires, the depth and speed indicator wires run from helm to transom so maybe it's in the wirers . If thats the case I'll try some ferrite beads and see what happens. Oh yea Gary my noise is like a Chuck-chuck-chuck, no pun intended

drjohn71a · Posted: Thu Oct 05, 2006 12:22 pm Post subject:

I have had similar interference problems which were probably caused by the depth finder cable running parallel and touching the antenna/power cable to the radio. Just moving the transducer cable a few inches away solved most of the interference. John

mikeporterinmd · Posted: Tue Jan 23, 2007 2:59 pm Post subject:

Hmmm...I finally got the new radio installed and powered up the GPS, and
now I have this problem. Well, at least I have a list of things to check.

I'll start with disconnecting the VHF antenna and see if the problem
persists. When I recently removed the PL-259 from its connector (it's a Digital
antenna), the connection didn't look the same to me as it originally
did. I wonder if I unscrewed something incorrectly and damaged the
ground connection.

FYI: the interference seems limited to 21 and 22 (I think - the
first one is the main Coast Guard channel.)

Mike

mikeporterinmd · Posted: Tue Jan 23, 2007 8:47 pm Post subject:

Well, removing the antenna connection from the VHF eliminated the
interference, so perhaps the interference is coming in from the
antenna and not the power feed.

The antenna is a new "Digital" brand 8' whip. The connector
comes attached from the factory. I checked it out again
tonight, and it looks fine.

I still have a Garmin 188. The unit causing the problem is a 188C; the
radio an ICOM 422. The 188 and 188C are plug compatable, so I connected
the 188, and no problem (188C is a much nicer unit!)

Next, I'll try a hand-held and possibly the old VHF.

I think it's an RF leak from the GPS. If I'm in chart mode, and use
the arrow keys to move around on the display, I can "hear it"
on the radio. Each key press makes a blip on the radio. Also, displays
that I suspect use more CPU power seem to cause more static.

Anyone else having trouble with a 188C and the ICOM 422?

The units are very close together, however I've unmounted them
and moved them about 7" or so apart, and no difference.

Disconnecting the GPS antenna did not help, so even though the
VHF and GPS antennas are close, I'm not sure that's it.

I moved the VHF cable away from the transducer cable. I also disconnected
the transducer - no significant difference.

Would the GPS be "broadcasting" through its power cable, or from the
unit itself? Would the ferrite beads help?

Mike

mikeporterinmd · Posted: Tue Jan 23, 2007 10:26 pm Post subject:

OK, the interference is present on a handheld that's at least 7' away
from the Garmin 188C. Channels 21 and 22 primarily. Interference
present without transducer and without GPS antenna. Guess it's
time to call Garmin?

Mike

rogerbum · Posted: Tue Jan 23, 2007 11:32 pm Post subject:

mikeporterinmd · Posted: Wed Jan 24, 2007 1:56 pm Post subject:

Stanley-J · Posted: Wed Jan 24, 2007 4:05 pm Post subject:

I started this post a while back and I tried everything I could think of. The problem was that it also occcured on my handheld as well so I didn't think it had anything to do with cables touching. I even slipped a very heavy shielded copper braided cable over the transducer cable and it still made noise on both radios. I know it's the transducer because when I turn off the depth sounder in the 188 menu it stops. I relocated the radio from one side to the other in the cabin. I changed the location of the antenna (temporarily) still the pulse noise. When I had it on my handheld in side the cabin then I figure I need some ferrite beads I'll try that next. I'll place #43 material beads on the transduce at both ends. I think I'll use the hand held as a signal tracer to help in the trouble shooting.

AstoriaDave · Posted: Wed Jan 24, 2007 4:19 pm Post subject:

S-J:

Not much of an electronics expert here, but if you are getting significant RFI from a device which is not supposed to radiate in the radio frequency range, I'd suspect some flaw in in its components or connections.

The fact that the HH picks it up when the HH is not near any wires means there has to be a hell of a lot being emitted -- radiated -- from your wiring system. IOW, the interference is not coming solely via wires directly to another unit, and it has to be very high power to radiate that far through-space.

I know this is an ugly thought, but is it possible the transducer itself has some sort of poor connection or other similar problem? Is it difficult to swap out the 'ducer?

rogerbum · Posted: Wed Jan 24, 2007 5:42 pm Post subject:

mikeporterinmd · Posted: Wed Jan 24, 2007 7:54 pm Post subject:

Tonights plan is to remove the GPS from the boat and power it from a
12V NiCad pack I have laying around.

I'll check into the menu option that controls the transducer. Didn't know
there was such an option.

Mike

mikeporterinmd · Posted: Wed Jan 24, 2007 9:19 pm Post subject:

First, let me say that the boat originally had a Garmin 188 installed.
The cables are roughly the same, so the installer used the old cable.
The new cable does have a large ferrit bead on it, so when I realized
this, I installed the new cable in the boat. No real change.

Moving inside where it's warm, I can power the 188C off of a Nicad
battery pack, and wave the handheld around. The interference
follows the power leads, for sure.

Photos of a foil wrapped Garmin GPS 188C

Well, I guess we'll see what Garmin tech support has to say. So far, their
ending statement was 'go see a professional'. A professional installed
the thing in the first place.

Mike