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VHF interference

Old 10-02-2006, 09:49 AM
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Default VHF interference

Wanted to check and see how you'd troubleshoot this. I have read previous threads but have not resolved the issue yet.

Getting major interference on VHF from engine and Lowrance LCX-26. At first I thought it was the Lowrance causing the problems and have read where others had this issue. But this weekend I noticed with the engine off and other electronics off VHF worked great. So to determine what the problems may be I turned on one thing at a time:

1) Engine on idle and Lowrance off - I could hear the up and down engine "whine" through the VHF and had to turn squelch way up to elimnate noise.

2) Engine off and Lowrance on - major static. If unplug GPS module still getting noise, and if turn off transducer also still getting noise.

I noticed my power wire is on the fuse bus with everything else and had been wire-tied to other wires so I cut the VHF power wire loose and moved them away (not far as this is all under the console). Also put ferrite bead on power wire and on antennae wire (although on antennae wire all I had was the kind you wrap the wire around - less effective than the bead?). Ferrites did not seem to help much or certainly not enough. Unless I turn the squelch almost all the way up there is so much "noise" the scan feature will not work.

How do I determine if the "noise" is coming through the power wires or antennae wire? That would really help narrow down the potential solution?

I guess first thing would be to hook the power to one of my Trolling motor batteries and see what happens, at least that would isolate the VHF from other power souces? Does the VHF do anything if you disconnect the antennae?

Old 10-02-2006, 11:29 AM
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Default Re: VHF interference

Try disconnecting the antenna coax. (DO NOT TRANSMIT). If the noise goes away, then you know it is being pickup up by the antenna and not the power cable. If the noise stays, then it could be coming from the power cable or being radiated directly into the case of the radio.

1. What VHF do you have?
2. Did any of the noise change when you put on the ferrite beads?
3. Did any of the noise change when you separated the wires?
Old 10-02-2006, 11:37 AM
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Default Re: VHF interference

Ray53DSC I believe are the numbers.

I did not notice change with ferrite beads or wire relo. Could have helped some I suppose but certainly not enough.

Will try disconnecting antennae and see what happens.
Old 10-02-2006, 12:07 PM
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Default Re: VHF interference

I was having the same noise problem with my icom 302 VHF. Noise from the motor and Raymarine DS 500x was driving me crazy. I removed the antenna cable and the noise persisted so I knew it wasn't an antenna problem. I put a noise filter on the power wire between the fuse panel and the radio.............problem solved!

Here's the part I used.
http://www.crutchfield.com/S-bYTpdEm...lter&i=003S15A
Old 10-02-2006, 09:11 PM
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Default Re: VHF interference

As I expected, no simple solution yet for me.

Troubleshooting report: Turn Lowrance on and
1) If I unplug antennae noise goes away.
2) Shortened length of antennae wire and added a new Shakespeare connector (one that only requires pliers). This was hopefully to see if mine was a shielding issue from a poor connector job previously.
3) Connected power to my TM battery just to further show its an antennae wire problem and noise was exactly the same as when connected to fuse bus.
4) Added ferrite bead to antennae and saw no decrease in noise.

For whatever its worth some channels are much worse. I notice now that on Channel 22 I cannot turn squelch up high enough to eliminate the noise. On 16 it takes about 2/4 squelch. No idea what this means.

Another interesting note - I get the same noise with the GPS module not powered AND the transducer turned off.......thus its the actual Lowrance unit causing the issue. Plan to call Lowrance but as I said in first post, I also have some engine noise interference that I need to get rid of. I did not start engine tonight so its possible engine noise could be coming through power cable. First I plan to resolve this graph intereference somehow.

Suggestions?
Old 10-02-2006, 09:17 PM
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Default Re: VHF interference

My Raymarine was causing mot of the problem but the noise filter soved it.
Have you given a cheap noise filter a try like I posted above? If it doesn't work you're only out $13.
Old 10-02-2006, 09:58 PM
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Default Re: VHF interference

I have not yet but I though this was what the ferrite bead was supposed to do. But more importantly, you determined your was a problem in the power cord right? I cannot hook the part you suggested to the antennae wire. I am willing to try it for sure for $13 but since my noise goes away when I unplug antennae I don't think a solution on the power cord is the answer - but I don't know much!
Old 10-02-2006, 10:37 PM
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Default Re: VHF interference

You can try adding more the one ferrite beads on the coax. I would also try adding a bunch to the Lowrance unit as well. Ferrite beads are pretty cheap. Out some on every wire of the Lowrance. You may also try separating the antenna coax from ANY wires associated with the Lowrance.

Also, how old is the VHF?
Old 10-02-2006, 11:37 PM
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Default Re: VHF interference

I have corresonded with Lowrance--and their solution is that VhF and Lowrance LCX 26C need to have separate power supplies directly from the battery. The electronics need to come directly from a house bank, not the engine starting battery. The GPS and FF cables should not run parallel to the antenna of the VHF.

I had another Lowrance (3300 C which also has a 2000 NMEA antenna, and used it, away from all other VHF antennas-with no change of the interference). I did ferrite beads on everything and it helps. I also used separate power cables for VHF and Lowrance. There is evidence that Lowrance is not shielding the cables to the standards they should (only to CE min stds). (incidently I also put foil around the screen and LCX 26, with no affect. There are a number of sources of noise filters for 12 volts--basically a capacitor).

At this point, my noise level is tolerable--and most is comming from the sounder. I am considering wraping it with foil tape (as used for heating ducts) near the console and antennas.

It is a real problem which Lowrance engineers/administration has choosen to ignore. They did not return my second E mail--which had information about shielding which would have helped. If Lowrance does not wake up, it will damage a good reputation and decrease sales of a great product otherwise.
Old 10-03-2006, 08:50 AM
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Default RE: VHF interference

The VHF is about the age of the boat I suppose 2003/2004.

The antennae wire is on the right side of the console, the Lowrance is in the center of the console on top and the fuse bus is on the left side of the console. The antennae wire cannot be further from the Lowrance wires.

I'll give more ferrites a try but I cannot see where separating power supply would help. Also, I only haveone cranking/house battery (19' bay boat) and don't want anything else running directly off battery. Also since mine is antennae "noise" power supply configuration should not be an issue.

I think it has to do with the Lowrance shielding. Like I said I thought it would be the GPS module or transducer power maybe but "noise " is there even when I trun sonar feature of and unplug GPS module - its the actual Lowrance unit causing the problem.

There is not a ground issue perhaps? What about a way to better shield the antennae wire - some kind of sleeve? It only runs about 2-3' from the antennae to the radio.

Old 10-03-2006, 03:26 PM
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Default RE: VHF interference

Palmettores, I've had noise issues in two different ways. I'll relate the stories in the hope it may help you. The first one doesn't sound like what you are describing but the second one does.

1) I had situation with a VHF and a Garmin plotter unit but it resulted in a buzz on the power supply cable. The cause was the Garmin unit screen dimming. At Maximum and minimum backlight the buzz was subdued. I presume Garmin control the backlight by switching the power on and off for varied lengths of time (pulse width modulation). The solution was to fit suppressors in the form of inductor/capacitor networks to both the Garmin and the radio 12v supply.

2) After fitting a Navtex receiver, the VHF went ballistic and the squelch was near the top of the range just to silence the noise. My boat is fibreglass but the cabin is a metal frame clad with ply and fibreglass the metal frame bolts through the hull and connects with the sea to give a ship's ground. When the Navtex ground wire was disconnected from ship's ground the noise virtually stopped. It appears that the Navtex receiver is electrically noisy and connecting its ground (not battery negative) to the cabin frame (ship's ground) caused the frame to be a source of noise sufficient to transmit to the antenna. The antenna mounting bracket (plastic) is very close to the cabin frame so the distance from the frame to the antenna is short. Now, ship's ground should ground this noise but it didn't. The solution, in my case, was to leave the Navtex ground floating by not connecting it to anything.

To prevent galvanic corrosion, ship's ground is not connected to the battery negative.

To test whether the noise is being received by the antenna, whilst everything is running and noisy, unscrew the antenna screen connector. Pull it back to make sure it is not touching the radio so the screen connection is broken and if the noise stops you are indeed receiving the interference via the antenna. There is no need to fully remove the connector but doing so shouldn't do any harm to the VHF provided you don't press the TX button. You are unlikely to stop this level of noise by adding ferrites to your wiring.


One other thing that comes to mind is an earth loop. Your signal cable screening should all be connected to one single point if possible (star wiring) and it should only be connected at one end.

JW.

Old 10-03-2006, 07:24 PM
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Default Re: VHF interference

JW, you lost me a little. There seems to be no doubt my noise, at least from the Lowrance unit is coming thu the antennae (when unplug antennae noise goes away). I am unclear on what you are suggesting to do? I have one black and one red wire to atatch to fuse bus for both the VHF and Lowrance unit. There are several other color wires in the VHF harness but i assume they do other things not ground.

How do I make sure ground is good to the fuse bus?
Old 10-03-2006, 08:12 PM
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Default Re: VHF interference

Hi palmettores, I was avoiding suggesting what you do because I don't know your boat. I was rather hoping something I said rang a bell with you for your setup and was a help.

Your Lowrance will surely have a screen around it's cables, how have you connected this? Does the manual recommend a particular connecting point for the screen? It could be the opposite of my problem and the noisy Lowrance needs to be connected to a ground to sink the noise.

The black and red are just the power cables and I don't see them as the cause of your problem. If your antenna is receiving noise, something is transmitting that noise to the antenna not to the cables.

I wondered whether your boat had a metal frame holding a roof or was part of a cabin and perhaps the frame was being used as a negative rail to the battery. If your Lowrance is noisy as my Navtex is and you had the screen connected to battery -ve, it would effectively be connected to the frame. I'm just guessing possibilities, of course.

It might be a help for you to draw what you have connected to each other and look for earth loops, disconnections or odd connections in your screening.

JW.
Old 10-03-2006, 09:36 PM
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Default Re: VHF interference

JW, your thoughts have been helpful. My boat is a fairly simple 19' center console - no cabins, T-tops etc (do have a metal handrail around the windshield which is close to both the Lowrance and VHF antennae but not touching any of it).

All console electronics run off console fuse buss - standard switches, stereo, VHF, Lowrance LCX 26. VHF antennae bolted to side of console and antennae cord passes thru console wall and then to VHF radio.

As to "screen around Lowrance cables", there is a silver "shielding" wire that instructions said to connect with the black, negative wire which are both attached together to the negative bar of fuse buss. The power cable had raw ends which I put female connectors on to attach to fuse buss and the other end is a Lowarance connector to plug into the back of the unit.

I did read on raymarine website that you can attach a ground wire to one of the screws on the back of the VHF. It says to then attach to ships ground - where would this best be?
Old 10-03-2006, 10:19 PM
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Default Re: VHF interference

I also read on raymarine website that the VHF and antennae should be 3' or more apart. Mine are not, more like 2' at best.
Old 10-04-2006, 07:06 AM
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Default Re: VHF interference

A proper installation would have three connections. +ve and -ve battery connections and ship's ground. Ships ground is the connection which connects with the water. On a steel boat it is easy but on fibreglass boats not quite so simple. It is the connection to which all the screening should run so that interference collected by the screen (shield) will run to earth.

On leisure boats ship's ground often doesn't exist. If you are using outboard motors it's probable that the metal of the motor is connected to battery -ve. Since the engine is in the sea it can also serve as ship's ground and I would guess that's why Lowrance suggest connecting the screen to the -ve buss. It's effectiveness will depend on your whole boat wiring.

Now, presuming your situation is as described above. It is likely the VHF has a floating ground (shield) for the antenna. The case (shield) of the VHF can be connected to the -ve buss but I suspect it won't make any difference. You could also try connecting the shield of the VHF antenna to -ve. This may interfere with the range you can transmit because, ultimately, this connection is going into the sea via your engine and this will give your antenna a ground plane. Depending on the design of your antenna this could be good or bad. Either way, it will do no harm to the VHF.

If you have left a service length of cable for your VHF antenna, you could disconnect the mounting and try moving it away from the instruments. If this works, try connecting the hand rail to -ve. Also, try disconnecting the Lowrance shield from the -ve buss. An earth loop can be very noisy and it's simply an earth (shield) connection which is made twice. This can be done inadvertently. It may be worth leaving the shields of the Lowrance and the VHF disconnected from -ve and checking with a multimeter to see whether they are internally connected to -ve. I would expect them not to be.

If you are sure your Lowrance is the cause of the interference, it is transmitting to the antenna and that transmission should be prevented by the shielding of the Lowrance. So you have to identify how this can be. It could be a faulty Lowrance unit where the internal shielding is not sound.

Be methodical and don't do two things at once without doing them individually first.

All this is just info that may give you clues. If you know it already, just ignore me. There'll be nothing new in that.

If you solve it, let us know the solution.


JW.
Old 10-04-2006, 07:52 AM
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Default Re: VHF interference

Long shot, is your engine lowered into the sea while you are testing?
Old 10-04-2006, 09:16 AM
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Default Re: VHF interference

JW, Lots of things to check out. Last night in the shop the motor was not in the water of course. I guess then you are suggesting I do most of my trials in the water so that grounding situation is the same as when the boat is in operation?

Before I shortened my antennae cable I should have moved it away to see how it performed. I can probably go by a local electronics place and borrow an antennae and see what happens with one not connected to the boat.

I also want to check that handrail. The GPS module is mounted to it and the Lowrance unit is very close to it. It could be a problem.

I'll keep you posted.
Old 10-04-2006, 06:37 PM
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Default Re: VHF interference

If you're going to play with the antenna, do as I suggested and plug the connector into the VHF but don't allow the sheild to make a connection. Let me know if that stops the interference from the Lowrance.

JW.
Old 10-04-2006, 08:21 PM
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Default Re: VHF interference

palmettores
Most marine VHF antennas "like" to have 3 feet or more of cable to help provide a ground counterpoise. This provides a better impedance match between your antenna and radioo. Also helps keep the radiated power coming from the antenna, minimizing the RF on the coax shield (outside).

Ferrite beads help to further supress stray RF on the *outside* of the coax. ...Will not help if the interference is being radiated by poorly shielded unit - It is recieved by the antenna just like intended signals. If this is the case, the only solution is to stop it at the source.

To to further rule out ground loops, turn on you "noisemaker". Just touch the shell of the coax connector to the VHF antenna connection (chassis). Don't actually plug in. Try with system power first. No noise (as with total disconnection) - it is a radiated signal being recieved. Worke on the noisy unit. If there on system power, but not there on isolated battery, a ground loop. Is likely involved. A combination of Gloop and radiated is also possible.
From your diagnostics, the interference is coming from the antenna.

I suspect you have radiated interference. Lots of ferrite beads on every cable as it exits the offending unit can help. As someone said, if unit has a ground connection, try with and without (sometimes helpful for loops or radiated . If radiating that bad is typical, the manufacturer *should* offer a fix. Good Luck!

If all else fails, wrap the unit in copper screen

Woody
Noran - 24 Albemarle Exp

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