VHF interference from Plotter/fishfinder plus ???

[Gene Morris]

I started a thread like this some time ago. I am still having an intermittent problem with radio interference while my plotter is on. The interference takes the form of squelching the radio to the extent that turning the squelch control will not eliminate the noise. I have placed ferrite beads at all the usual locations. This seamed to help some but the problem is so intermittent that I really don't know. While fishing yesterday the problem was persistent so I turned the fixed VHF off and decided to use my hand held. I had the same problem with the handheld everywhere on the boat. I may be able to take the boat to Portland Or where the electronics were installed, but that will be a great inconvenience. Any suggestions?????

On another note we have a coffee maker on board. When I key the mike on the vhf I will trip the breaker on the GFI outlet. It worked fine before yesterday. This only happens if the coffee maker is plugged in. Other appliances don't have this effect. I installed the outlet on the top of the hanging locker in January.
WHAT THE HECK??????

Thanks
Gene Morris


Any suggestions will be appreciated.

[mikeporterinmd]

I have posted some long threads on the topic of chart plotters causing
interference on certain VHF channels. So have others.

Some units are so bad they are nearly unusable. I replaced a Garmin
GPS 188C because of the racket it made on channel 21, I think.

I replaced it with a Lowrance LMS-337C DF. At first I thought it was OK, then I
remembered to check the weather channels. It too made a racket on
one of the VHF channels (3?). However, I updated the software and the
problem went away.

Specifically, the Lowrance made noise when reading from the chart chip.
If you went to a chartless page, no noise. Use the built in charts, no
noise. I think the updated software probably read from the chart chip
in a more efficient manner so the electronics make less noise. You can still
hear blips when it reads from the chip, but it does not cause a problem.

I was going to write to Power Boat Reports and ask them to start including
a test of this sort when they evaluate units, but, well, that would be
pointless (PBR is no more).

Check out my photos of the GPS 188C. If you cover the entire unit in
foil and wrap your hands around the head, you can limit the RF. Also:
I returned the unit Garmin and they acknowleged a design flaw in the
unit. Too old to fix or get a credit. I detailed the problem in a ad on
Ebay and someone bought it any way. Maybe they don't listen to VHF.

Mike

[thataway]

I have written about this problem, both on this forum and on THT.
I also discussed this at length with Ben Ellison (Electronics editor for Power and motor boat, and Panbo blog).

Basically the VHF and Plotter and depth sounder are best connected directly to the battery (I prefer a separate electronics battery)--in reality this is difficult to do.

Next, the VHF and GPS antennas should be at least 3 feet apart. The wires for antennas or power should not be run parallel to the other units wires/antennas. Again, difficult but not impossiable to do in a C Dory or Tom Cat.

We had the same problem, mostly with the Lowrance XCL 26. Part of the problem is that there is less insullation (braid shield) than is ideal, especially for NMEA 2000.

I agree that if you surround the GPS/plotter with foil, it will help--but we have to be practical. You have done the beads, which is what made the most difference for us. Have ferrite beads on the power, antenna and data leads--all of them. We also re-routed some of the leads (antenna and power)--plus we went with separate batteries/and larger power leads.
As I have said before, I feel that the wiring on the stock boats is a little small. On the CD 25 I just added another #8 set of wires for the Electroncis, as I did for the TC 255. (I guess another way to go would be to tap off of the windlass wiring--but that has its set of problems).
We do have a separate fues block for the electroncis. You want to be sure that the voltage is up there --low voltage is one of the major problems with electroncis.

We have a little interference--but it is miminal (Two chart plotters, one with fishfinder) and two VHF radios,

[mikeporterinmd]

Actually, I found the interference to be so loud that foil and something
that approached the density of my hands was required. Actually, I did
not try my hands without foil, so foil may not help.

It seems obvious to me that manfuctures are not even testing for this.
I'm not talking about an annoying blip, blip, or a slight buzz. I'm talking
all out blasting. A signal so strong it completely wipes out a very
strong VHF weather signal.

Me thinks the FCC should rethink self certification for these types of
devices, but that would take a rather strong consumer oriented lobby, and
I doubt that exists.

Either that or draft something into the spec that is a little stronger
than "should", and if it doesn't work, the device must not be used.
Which pretty much leaves the consumer holding the bag unless the
device is bought from a good store.

Mike