Transducer radiating signal over VHF

[Carl]

Wondering if anyone may have an answer to correct this problem.

My friend has a fairly new Garmin Depth Finder that creates havoc with his VHF radio. Originally the transducer was the puck style and we thought maybe too close to wiring or broken shielding in the transducer wire, so he bought one of those stern mounted jobs and still has the tranducer emiting the clicking over the radio, can't hear a thing. He went so far as to buy a handheld radio and even that can't be heard unless he shuts off the depthfinder.

Any thoughts other then don't use the radio when using depthfinder or toss both and buy some new stuff.

He spoke to Garmin and they told him to move the units farther away from each other. He has them about as far as they can be positioned in his boat. Still the handheld can be 6' away from both and continues to have the transducer clicking over everything else.

Both units are wired to different batteries.


Thanks,
Carl

[JP Dalik]

Are both units bonded? If not try that.

[In Memory of Vicroy]

Carl, its a grounding problem in the sounder cable to the ducer. That cable is coax, meaning one hot wire in a sheath of braided ground wire. The ground sheath is not grounded to the 12v negative, simple as that.

UV

[Bruce]

Take a seperate 12v battery and hook up the depth finder to it. Power up to see if its still doing it.

If so then also hook up that VHF. If still doing it you've eliminated the posiblility of a ground loop problem and its an rf problem. That is maybe inside the display on the ducer cable socket the shield as UV described is not soldered well to the socket or on the pc board depending on construction.

If it goes away then look and make sure the -12dc grounds are solid back to the battery and he is not somehow using the bonding system as his ground creating a possible ground loop.

Also most electronic units have some sort of shielding inside either in the way of a metal case, foil covered paper,a choke or coil which could be bad or have a bad solder joint.

Doubt its in the ducer cable since both ducers produced the same results. Chances both being bad is slim.

[Carl]

Finally some information we can do something with.

Thanks I will go thru the process spelt out for me and hopefully come up with an answer. If not...at least we have something else to look for.

To check the unit, if it comes to that, could I run a continuity test from the units ground incoming lead to the outer part of the transducer socket? Would it also be okay to run a ground wire directly to the outer socket.

Thank you again UV and Bruce.

[Bruce]

A continuity check due to the fact that the boat is in water, bonding and ground systems are tied together in most cases and leakage all over the place I think is useless unless you are actually checking one end of a detached wire to the other end of a detached wire.

You could check from the ducer socket to the ground stud if it has one otherwise the socket shell may be connected only to the internal shielding and it may appear to be open.

Way to much leakage that could give false readings in a boat.

I'm a big proponent of running a #8 black from the battery or -12v buss if there is one to the bridge for the electronics and not use the -12v system already up there.
Mostly due to ground loop and possible rf interference.

While electronics have to pass some FCC mandated rf tests, I've found a big difference in electronics. For example the current cell phone I have is a Motorola Razor. Its the only cell phone that I've had that interferes with the truck radio while in operation.

Thats why they want us to shut stuff off on take offs and landings.

[Carl]

I was thinking of just testing the unit itself. Remove leads going to sounder and check continuity from the ground lead to the outer part of the coaxial fitting.

I check out what you mentioned and see what comes of it...if I need to go further I cross that bridge then.
Thanks