Very strong RFI on VHF from sonar

[fisherman73]

I have recently replaced my old chartplotter with a new Raymarine A57d. On my first outing everything worked perfectly and I was amazed at how well the unit worked. A few months later I was able to head out for my second trip since I had replaced the chartplotter. I was picking up a very strong pulsing static on most channels on my vhf. This noise is so strong that squelch has no effect. I was saving up to replace the radio anyway as it was a bit old, so I went ahead and replaced it with a new Raymarine Ray55. No change on the noise. After some diagnostic time. I realized that it was coming in via the antenna from the transducer and only on the 50khz mode. The noise will go away with either the antenna or the transducer disconnected. Here is what I have done so far.

Replaced radio
Replaced antenna
Rerouted cables
Performed volt drop tests on powers and grounds and ran redundant power and ground
Replaced transducer and cable with a unit that Raymarine sent me
Checked to see if I could pick up noise w/ handheld Vhf. no noise heard.
Checked connections on all units.

The proximity of the Radio to the Chartplotter is about 6 feet. The Proximity from the antenna to the Chartplotter is about 3 feet but separated by windshield.

Again the unit did function properly in the current configuation one time. It sat over the winter (fairly mild climate, rarely below freezing) and then the problem began to occur. I am thinking that it may be the chartplotter itself at this point. I would love any input that you have to offer. Thanks in advance !

 

[Splat]

Re: Very strong RFI on VHF from sonar

Pulsing would tell me it's rf leakage from the transducer signal. Where do you have everything grounded? I would re-check cables, make sure your antenna cable isn't routed along the same path as the transducer cable. Also check the cable for kinks or other damage. On the end of the antenna cable, check the pl-259 connector for damage or corrosion.

Use of a few ferrite chokes may help with this problem as well, but it's odd if it's a new problem that began without changing anything else in the boat.

Bill

 

[fisherman73]

Re: Very strong RFI on VHF from sonar

Pulsing would tell me it's rf leakage from the transducer signal. Where do you have everything grounded? I would re-check cables, make sure your antenna cable isn't routed along the same path as the transducer cable. Also check the cable for kinks or other damage. On the end of the antenna cable, check the pl-259 connector for damage or corrosion.

Use of a few ferrite chokes may help with this problem as well, but it's odd if it's a new problem that began without changing anything else in the boat.

The grounds are both on a ground strip that is fed by a 8 gauge wire to the battery. I have done volt drop tests and ran a redundant ground directly from the battery as well and had no change.

The antenna, cable, and pl259 I replaced trying to fix this problem with no change. The cables are not together and I have even temporarily moved them further apart to see if there is a change. The transducer and cable I have replaced with another new unit that I temporarily installed with no change.

I agree it is odd that the problem did not occur immediatly after the install. I actually have had this boat for many years with an older sonar unit and radio installed with all the exact same routing of cables and no problems. I understand about the use of chokes. I have not tried any yet but I am confident that the noise will be unchanged as even squelch full up has no effect. It is a full hit on the meter on the radio.

 

[Art Bernard]

Re: Very strong RFI on VHF from sonar

You might look into getting some mu-metal wrap for shielding your cables. I've used this in the navy for isolating and getting rid of interfearence, and it works well in car audio to get the alternator whine out of your speakers.

Art

 

[dingbat]

Re: Very strong RFI on VHF from sonar

I'm running a 1 kW Furuno sounder that is mounted less than 36" away from the VHF. The power, ground and transducer cables are all run inside the same 4" diameter rigging tube back to the batteries. I ran a seperate RF ground and Furuno supplied a ferrite for the power cable. I have no noise problem at all.

Here is your RF ground connected?

From your manual

RF ground
Use a dedicated earthing plate (e.g. dynaplate) in contact with
the water.
? Ground cables may be routed to a common point (e.g. within the
switch panel. With a single (appropriately rated) copper braid
connecting to the earthing plate.
? Use flat tinned copper braid, 30 A rating (1/4 inch) or greater.
Equivalent stranded wire diameter 4mm or greater.
? Keep the length of the earth braid as short as possible.

Suppression ferrites
Raymarine cables may be fitted with suppression ferrites. These are
important for correct EMC performance. Any ferrite removed to facilitate
installation must be replaced in the original position immediately installation is complete.