Radio / Fishfinder Interference Help

[sdbr911]

Asking for help here if anybody knows......

I bought a used boat recently and I have discovered that the fish finder is causing some sort of interference with the radio. When the radio is on, it works fine. When the fish finder is turned on also, the radio emits a constant click...click...click... The clicking goes away when I turn the fish finder off again, so I know that the fish finder is the cause. They both work fine but it gets annoying to keep hearing the click....click....click from the radio.

Any ideas on a cause or how I fix it? Here is a pic of the console.

Thanks

[Steve-o]

I can hear my transducer transmit pulses when I am close to it, which does sound like faint clicks at about once per second or faster. Is your click frequency similar? If I had to guess, I'd say your transducer cable and radio power leads are bundled together. Depending where your transducer, wiring bundles and batteries are, someone might have routed the cable from the stern all the way to the console which would require you to do a bit of disassembly. But maybe you're lucky and the offending run is located right inside the console and easily fixed. If the wire bundle will take a lot of work to get apart, you could first try powering the radio via a separate set of wires that do not come near the transducer cable. Good luck.

Edit: I don't see your antenna in the photo, but I imagine it is on the console and that the coax cable leading to it is not going far, but I suppose this is a possible source as well if it is right next to the transducer cable.

[Kahuna]

That is possible. You could also have a bad ground from the battery to the dash.

[dugout]

That is a radio marketed by Shakespeare, I believe, and was kind of known as a noise sponge with terrible RF rejection. Add ferrite beads to the power cables at the back of the units or replace the radio.

[Man-O-War]

Instructions say to mount GPS/finder away from compass/radio/radar...

[Mattedhead]

Maybe rewire w/ a shielded cable? I am far from an expert though.

[BLACKFIN]

What type of "radio?" Can't see or tell by your description. VHF? SSB? Probably not grounded sufficiently - the radio I mean.

[Kahuna]

That's what I was saying. A bad ground to the buss bar will force current through the transducer in some instances looking for a return path. I saw one that when you keyed the mike the bottom finder screen went apesht. I ignored it for a couple of weeks and ended up replacing a prop and shaft.

[Steve-o]

That's what I was saying. A bad ground to the buss bar will force current through the transducer in some instances looking for a return path. I saw one that when you keyed the mike the bottom finder screen went apesht. I ignored it for a couple of weeks and ended up replacing a prop and shaft.

Kahuna, that's very interesting....could you explain this further for me? I have some electrical knowledge but I am not an expert (my background consists of some physics classes and lots of wiring on my own boats). What I don't understand is how the current is going to get into the transducer cable? A poor ground will be seen by the radio as a lower voltage (potential between + and ground), and probably result in weak transmit power, which you could measure with a SWR meter. The only return path for current entering the radio is the ground wire to the bus bar or battery, etc. Radio antennas use coax cable to minimize EM current induction in wires the run near, so I'm a little stumped as to where the interference came from, unless there was something wrong with the radio and it leaked transmission signals into the power leads, but I'm just speculating there. Was this particular fishfinder using a foil shielded transducer cable (like Airmar)? Since you found and corrected the problem I would like to hear more....I have a hard time picturing what you describe. How was the running gear involved?

[sdbr911]

I can hear my transducer transmit pulses when I am close to it, which does sound like faint clicks at about once per second or faster. Is your click frequency similar? If I had to guess, I'd say your transducer cable and radio power leads are bundled together. Depending where your transducer, wiring bundles and batteries are, someone might have routed the cable from the stern all the way to the console which would require you to do a bit of disassembly. But maybe you're lucky and the offending run is located right inside the console and easily fixed. If the wire bundle will take a lot of work to get apart, you could first try powering the radio via a separate set of wires that do not come near the transducer cable. Good luck.

Edit: I don't see your antenna in the photo, but I imagine it is on the console and that the coax cable leading to it is not going far, but I suppose this is a possible source as well if it is right next to the transducer cable.


Yes the frequency of the clicks is about 1 per second. The antenna is mounted on the right rear corner of the boat. The radio is a Shakespeare VHF.

Your thought about the cables being too close makes sense. I will check the wiring and the ground connections.

I was thinking about replacing the radio anyway. This one works but I think it's as old as the boat (1994) and the new ones have some nicer features.

Thanks for the help guys.

[sdbr911]

Instructions say to mount GPS/finder away from compass/radio/radar...

The console setup that is pictured is the way the boat came. As you can see, there isn't a whole lot of room. I haven't calibrated the compass, but it seems to be right on with what GPS reads. I guess I could spread them out a little, but space is limited.

[Kahuna]

The ground from the battery or feed to the buss has a some resistance ( remember we are only dealing with an EMF of 12 volts) probably not completely open at this point. The exterior of the thru hull is negative ground and within a foot or two of the lower unit or in my case the shaft and prop which were properly grounded. Keep in mind although the key switch and gauges are also on the dash they run on an independant circuit of what we are discussing. You normally have a 12v feed and ground to the dash for accessories.

So the radio is looking for ground because the buss bar ground has failed. The next lowest potential is the ground coming from the transducer which is also on the negative buss bar via 1 foot of saltwater to the lower unit or in my case a stainless steel shaft very grounded via the engine. Current flow in salt water between two dissimilar metals is a bad thing. I hope this makes sense

[tbare]

The ground from the battery or feed to the buss has a some resistance ( remember we are only dealing with an EMF of 12 volts) probably not completely open at this point. The exterior of the thru hull is negative ground and within a foot or two of the lower unit or in my case the shaft and prop which were properly grounded. Keep in mind although the key switch and gauges are also on the dash they run on an independant circuit of what we are discussing. You normally have a 12v feed and ground to the dash for accessories.

So the radio is looking for ground because the buss bar ground has failed. The next lowest potential is the ground coming from the transducer which is also on the negative buss bar via 1 foot of saltwater to the lower unit or in my case a stainless steel shaft very grounded via the engine. Current flow in salt water between two dissimilar metals is a bad thing. I hope this makes sense

Wow,

I figured you ran aground when your bottom machine quit :confused:

t_bare

[Steve-o]

So the radio is looking for ground because the buss bar ground has failed. The next lowest potential is the ground coming from the transducer

Aha....that wasn't clear to me the first time. I thought you meant poor connection between radio ground and the ground bus. Thanks.