VHF interference from my Garmin 188

S

Stanley-J

New member
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.
 
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
 
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?
 
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
 
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
 
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
 
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
 
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
 
mikeporterinmd":3ixq7ee3 said:
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
Click to expand...

I've got the same problem with interference on my radio from my sounder. If the pulses you here are spaced at roughly 1 second and the spacing changes depending on the depth range, I bet it's your sounder. I tried moving my antenna cable away from the sounder cable with no relief. My current theory is that the current draw/push to the transducer is radiating either from the cable itself, from the power lead or from inductive coupling to another cable. My next step (mind you steps may be separated by months...) is to power the sounder from a separate battery with a very short lead - just temporarily to see if that solves the problem. If it does, I will assume that the current draw on the power lead is resultin in radiating the signal. If not, I will assume that the current push to the transducer is the probem and that some additional shielding/grounding is necessary on that cable.

Maybe an electronics whiz like Les (who has probably seen multiple variants of the same problem) can make other suggestions.
 
rogerbum":180jvwtu said:
mikeporterinmd":180jvwtu said:
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
Click to expand...

I've got the same problem with interference on my radio from my sounder. If the pulses you here are spaced at roughly 1 second and the spacing changes depending on the depth range, I bet it's your sounder. I tried moving my antenna cable away from the sounder cable with no relief. My current theory is that the current draw/push to the transducer is radiating either from the cable itself, from the power lead or from inductive coupling to another cable. My next step (mind you steps may be separated by months...) is to power the sounder from a separate battery with a very short lead - just temporarily to see if that solves the problem. If it does, I will assume that the current draw on the power lead is resultin in radiating the signal. If not, I will assume that the current push to the transducer is the probem and that some additional shielding/grounding is necessary on that cable.

Maybe an electronics whiz like Les (who has probably seen multiple variants of the same problem) can make other suggestions.
Click to expand...

I disconnected the sounder (tranducer). The GPS head unit saw the
disconnect and turned off output to the unit. So, not the sounder in
my case. There is a 1 second pulsing, though.

I'll try walking around the boat tonight with the handheld and see how far the
signal radiates and what the pattern is. A haldheld sure is useful in a situation
like this because you can discount problems with wires near each other.

Also, not sure if you know this, but a Garmin GPS 188C contains both a GPS and
a place to plug in a transducer, so I guess that makes it a combo GPS/Sounder
unit. That being the case, your statement of "I'll bet it's the sounder" is correct!
But, how to fix it?

Mike
 
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.
 
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?
 
AstoriaDave":2i073ybe said:
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?
Click to expand...

That's roughly what I was trying to say. But at this point, I'm not sure what is doing the radiating. The way I look at it there are two "lines" down which significant current flows for each pulse of the transducer. One is the cable to the transducer itself as the sounder has to drive the generation of the pulse by running current to the equivalent of a speaker on the other end. The other is the power draw from the sounder. E.g. the sounder has to get the energy from the battery and maybe that power draw is radiating. Perhaps the latter is less likely, but it's much easier to check simply by powering the sounder from a short lead to a nearby battery. My thought was to pick up a small 12V lattern battery and hook that up to the sounder to see if that solved the problem. If so, then I know it's not radiating down the sounder cable. If not, then the sounder cable is the most likely problem.

If the latter is the case, then I'm not really certain how to solve the problem but it could be that the shield around that cable is not effectively connected to the ground of the system and that will solve the problem. Again though, I'd really like to hear from someone whose looked at lots of similar problems and who knows what is the most likely source of the problem.
 
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
 
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
 
I'll try to apply a little my knowledge from 30 some odd years of playing with all manner of radios.

a. I agree with AstoriaDave that whatever it is, it is being transmitted at a relatively high effective power. However, I don't think it is on the primary VHF frequency but some intermediate frequency (IF) in common between the radio(s) and the sonar.
b. It is likely something failed since in the past it has worked. I would say the transducer is emitting RF on a intermediate frequency used by both radios. At the intermediate frequency the power levels in a radio are quite low, so it wouldn't take much to cause a problem.

Now if I am wrong, please remember I was a forestry major in college.
 
tpbrady":61h522wb said:
....
b. It is likely something failed since in the past it has worked.
Click to expand...

I have no reason to believe it ever worked. The previous owners
of this boat were not likely to listen to channel 21 and the previous
VHF only had a dual watch function, not full scan. I only ran the
boat a few times before the end of the season and didn't put channel
21 on dual watch.

Even though I have installed a new radio, all symptoms can
be demonstrated with both the new VHF (ICOM 422) and an ICOM
handheld. So, I don't believe it's the new radio.

Indeed, the problem can be demonstrated in my office without
sonar or VHF antennas or lots of wires or anything like that. See
previous post.

I have no opinion on sub-frequencies or anything like that. No knowlege
to base any such opinion on!

Mike
 
Stanley-J":1ktdauuw said:
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
Click to expand...

Is your unit a 188 or a 188C? 188 is greyscale, 188C color. I still have
a 188, and it is apparently 'quiet', but I haven't done extensive testing
since it was not installed when I bought the boat.

Mike
 
This is a fairly common problem. I had it with a Lowarance Depth Sounder/Chart plotter and it has been discussed with other brands on some of the electronics forums.

The manufactures will say: Place the vhf antenna 3 feet from the GPS antenna. Run the antennas at least a foot apart. Keep the radio 3 feet from the GPS screen. Keep all power supplies separate, power from separate batteries. Obviously these folks don't own C Dories!

The best "fix" is ferrite beads--Mike is correct. First put them on the Power cords and the GPS antenna input. As a last resort on the VHF antenna. There are some who feel that putting a choke on the VHF will decrease the output to the antenna. My tests have not confirmed any RF output decrease when doing this.

Part of the problem is that with the competative pricing that less copper is used in the shields of the cables to and from the GPS antennas. Some folks have thought that color screens were a culprit--several (including myself) have tried shielding both the screen and the radio with foil, and found no help.

Also I found that the problem was less on the water than in the trailer.
I have a very minor amount of RF on one of my antennas--but with the ferrite beads it is minimal.

The Digital antenna has a mini connector which screws into the PL 259 and that be what you noticed.

Regards,
 
I was thinking about powering the two units from different batteries.
I've wired the VHF to the starting battery before under the idea
that if the house bank died, you would still want VHF, and VHF shouldn't
drain the starting battery.

But, as you can see, that isn't going to help me with this unit since
my tests with a nicad battery running the GPS and the handheld
still showed lots of interference. Connecting the GPS antenna or
not doesn't seem to matter. There was a slight amount of noise
comming from the disconnected transducer wire.

I do believe it is the color display that is causing the problem.
By way of evidence, if I plug in the old 188 B/W display, the problem
goes away. I think the RF from the display radiates out through the
power lines. I was able to get interference on the boat much farther
from the display on the boat than in the house. On the boat, I was
still "near" the power cables....3-4' probably. In the house, I could
move the handheld along the power lines and hear the noise. But,
the big blast came from the display. I didn't check the GPS antenna
wire for RF.

I think I'm going to call Garmin, get them to say this shouldn't
happen, and return the unit for repair. If I can get them to
agree that a repaired unit won't exhibit this behavior, perhaps
I'll get one that works. I can't believe all 188C units do this. Or
if they do emit RF, at least it won't be in a range I'm interested in.

Anyhow, with all the ideas everyone has given me, I don't
think I'm missing anything obvious. There are a few similar threads
on the internet, but none have resolutions. I'll get one - we'll see if
it's "bought another GPS from ..." or Garmin fixed it or the
boat handles funny...could 500 lbs of ferrit beads cause this?

Chuck: you might consider removing your GPS from the boat
and powering it up elsewhere. If you have a handheld, then you
can check for interference away from the boat.

Mike
 
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