[Skid Row]

I'm having a problem with my LCD fish finder and VHF radio, I can't have them both on at the same time. What happens is I get feed back from the fish finder that distorts the radio. I have had this problem from day 1 but I always thought it might be my wiring, so I finally decided to rewire them both. SAME PROBLEM, then I thought maybe the transducer cable is resting on a power line so I rerouted it. SAME PROBLEM, then I thought maybe the antenna cable might be resting against something so I rerouted that, SAME PROBLEM. Is anyone here familiar with this problem, or have any ideas or suggestions on how I might correct this problem.

 

[happyhrs]

feedback

If you find out the problem please post the solution,I am having the same problem with mine. I have come to the conclusion that the FF is mounted too close to the vhf. They are both in the overhead electronics box.
thanx
Bill

 

[max171]

i too have a similar problem, when i transmit on the vhf, i get lines on my fish finder....someone told me that the vhf cable and the transducer cable are too close together ,but after some adjustments the prob persists.
anyone having similar problem, please advise...thanks
max

 

[MakoMike]

Guys,
FWIW, I have my VHF mounted right next to my fish finder and don't have a problem. OTOH I have CRT fish finder, though I don't think that makes a difference. I would look at the other end of the string, where the VHF antenna and cable and the Dpethsounder transducer and cable are. That's where your probably getting your interference. Try slipping a piece of sheet metal between the two units and see if that solves the problem, I'll wager it won't. But if it does, it means that the interference is from the units themselves and you can take steps to isolate them.

 

[617430]

This may be tough, but you may have to move your VHF antenna and radio away from the depthfinder; the depthfinder sends/receives pulses that you are also picking up on your radio. I had a similar problem with a Garmin 120 GPS a few years ago before Garmin began advising to keep the GPS and radio at least 3 feet apart. In my last three boats, I've had no problems but it's not always doable on a narrow console.

Go to the manufacturers websites and ask for tech support. They usually cut to the chase on the right answers.

 

[togmaster]

what models?

Guys this is a problem with certain machines I have seen it happen. A company called Nemar makes filters that will stop this. I have called companies to complain about it. My North Star and Raytheon had the problem.
I believe it is caused by a freq. response being smoething operating or transmitting at the same frequency will cancel each other out. Like I said try a Nemar filter on both of the units this solved my problem. It seemed the power was the cause of it. Dc current travels from negative to positive. There was a feed back between both machines by using the Nemar filter it solved the problem. If that wont work calls the company and tells them what 2 units are having a conflict and I bet they will know about it or have a solution? Nauticot is also correct having the VHF ant to close to other units can create a loop and interfer with units. You must have at least 3ft. clearence from the VHF ant. Another suggestion is to wire the color scope directly to the Battery with a fuse holder. if they are on the same terminal block this may cause a problem also. good luck and let us know if you fix it?

 

[seaslug44]

Please post what model fishfinder and vhf radio. I have had this problem too with my fishfinder but I isolated it and found the cause (although I haven't found a solution).

My fishfinder also has a built-in C-map GPS chartplotter. My interference is coming from the GPS antenna cable. It transmits a slow pulse over both my vhf and my fm radios!! The GPS mushroom antenna is mounted seven feet from the other two antennas, but the cable goes right past the units under the dash.

I was thinking that I need some sort of "antenna wire coax SHIELD" that could be slipped over the antenna wires to block the signals. I would think that it would have to be constructed with a lead lining to be effective. I have just never gotten around to researching it. Anyone here know if such an item exists?

 

[MakoMike]

Doc,
Try a place that caters to sailboats. They use a lot of halyard covers that may do the job.

 

[seaslug44]

MakoMike,

Great advice!

 

[treypescatorie]

EMI ( electromagnitic interference)

You can try ferite beads. They are used to cancle the emissions that radiate from electronic circuits. You can try using them on the power/transducer cables at the point where they exit the vhf/fish or any other equiptment that you suspect is radiating.
If you look on your computer they use them on the power cord or on the monitor cable.
Not sure if they have them at radio shack, but they should have them at an electronics supply house.
Good luck
Treypescatorie

 

[seaslug44]

Treypescatorie, always wondered what those bulbs were on the power cord. Do you think they will diminish the transmitting signals?

 

[treypescatorie]

Doctorfish,
The ferrites do not affect the transmitted signal. They are used to filter out any unwanted signals that are emitted from wires/cables thru out the system. Some times the wires or cables act like antennas and pick up noise or other un wanted signals and re transmit them.
If I had an EMI problem I would:
1) Keep my cables as short as possible.
2)Try re routing them.
3)Try shielding
4) Try the clip on ferrites.(use them on wires/cables as the exit the fish finder/vhf or other equiptment you suspect might be causing the problem.

PS Its not a guarantee that ferrites will solve the problem.

 

[Skid Row]

I see that I am not alone with this problem. I thought it was just me.

To answer some of your replies, I am using a raytheon L470 fish finder and a uniden mc535 VHF.

When I started rewiring them both, I tried each unit directly to the battery. When I rerouted the wires, cables (transducer & antenna) I made sure they were not touching anything. My antenna is about 3' from my vhf and my FF is about 2' from the vhf.

When I put on both units at the same time nothing happens to the ff just the vhf, I get beeps like morse code only a little slower ( I guess sound wave echoes) coming out of my vhf and can not here anything else but static.

All of your replies above made alot of sense (Thanks) and I will follow through with each and every one. If any one has anymore ideas or suggestions please bring them on, thanks again.

 

[622073]

Hi, have the same problem with a twist... Last year I had an 8' ant and had no problem, this year, changed only the ant (still using the same Standard Horizon VHF and Ray FF L375) Now I have the problem... Equipment wiring is in the same location. The only thing that's changed is that the coax on the antenna is longer (3') as they recomended, the other was 18" (about a full wave for the frequency we're working on) So, going to change back to 18" (hopefully that'll stop the harmonics from getting into the radio.)

I have a suggestion though... Turn the squelch down and scan for the frequency that you hear the tones on best, then move you wiring around to different locations. I've found that if I move my coax 2" to the left here... the interference goes away, or move it 2" there, and it goes away... Also, My FF is mounted 3" behind my radio. Like I say, probably your antenna or coax in right in the field created by the FF... Cheapest solution is to just move the wiring around to a different location... also try to shorten the power leads (everything is tied together on mine, no problems with the other antenna) the power leads can act like antennas... Last year I was in my tin boat in Smithtown Bay listening to conversations in the Great South Bay... New antenna (coax length, or height of the antenna load coil (top) seems to be the problem), now I'm lucky if I hear CT...

Hope it helps some...
If I confused more than helped... just post a question..

Richie (N2NIT - also a Ham Operator)