VHF Interference

[Patrick]

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My Bayliner boat has a 110v/ 12v frig. When the frig is on the 12v side, my VHF radio has a loud buzz comming from it. I tried direct to the battery, no change. Went to the electronic store, they sold me a " choke"(2 half magnets that fold around the power wire.) No change either. Any suggestions???

Patrick

[SomeSailor]

Run down to your local Radio Shack. Grab a handfull of 0.1µF (micro-farad) 50V, non-polarized, ceramic capacitors. They're like $1.89 a dozen :)

Bare the power and ground leads for your VHF temporarily. Twist on one cap between the two (red and black).

Temporarily wiring a cap like this will dump any slight RF noise coming up the line from the fridge on the DC side. If that fixes it, wire it all in permanent.

If it doesn't... lemme know and we'll go at it from the other end.

http://www.iboatnw.com/gallery/data/media/26/RadioNoise.jpg

[Patrick]

Great Idea.... I'll give it a try, and let you know Thanks :>)

Patrick

[Pegasis]

If you can get to the refer motor, I think you would be better off installing those cap's closer to the source of the noise so the noise is in less of your electrical system.

At least this is my experiance from when I used to race electric RC cars. We placed caps on the motor connections and if this wasn't enough also the battery motor connector where it plugged into the speed control.

[SomeSailor]

It's just easier to get to the VHF wires, and electrically accomplishes the same thing. It passes any AC to ground as it might be coming up the power leads.

I actually suspect that the noise isn't from the DC motor so much as the power supply. These units step up the 12VDC to 18VAC while on battery power, and use a 15:1 transformer to bring the 120 down. If you're getting noise all of the sudden, it's likely the power supply filtering that's dead.

I'd try the simple stuff first. It's also possible you're picking it up through the receiver, but lets try this first.

[Patrick]

I installed the cap's you specified. One lead to positive one to negitave. no change. I know it's not comming through the antenna. It still does it after I unplug it.

I'll try the caps on the frig 12v leads next.

Now I have one cap on the 12 v leads supplying the frig. And one cap on the 12v leads to the vhf. NO CHANGE. still a loud humm, everytime the frig cycles on, while on the 12v side. It doesn't make any hummm while on the ac side. also this is the only electronic device it affects on board.

Patrick

[SomeSailor]

It could indeed be picking it up on the antenna side. Try a couple of filter caps on the DC input for the fridge as well.

[Patrick]

Two caps on the 12v input to the frig? On the same splice, or in two different locations?

Ps. Im going boating this evening. will pick up again Sun. eve when I return.

Thanks
Patrick

[SomeSailor]

Yes. The idea is a capacitor will conduct AC. You can then "short" this noise (AC) to ground and the DC is blocked by the caps. When you can find the source of the noise, you can shunt it to ground.

[Patrick]

One cap on frig 12v wires, one cap on 12v wires to vhf. Still no change. do I add more caps to same locations?

[SomeSailor]

OK... So you've placed caps on both the VHF power and fridge power and it's still there huh?

Let me confirm one more time... you get the noise anytime the fridge is on AC and this is both with the VHF antenna on or off?

If that's the case we can move on to the next process of elimination. To rule out the 12VDC side of you boat, you'll need to borrow a separate battery. The easiest way is to pull your car alongside and spool up a couple of wires twisted onto your cars (not running) battery and then up to the VHF power input. A pair of jumper cables will get you within a few feet of the radio.

Make sure you disconnect the boat's source. If the noise is NOT present when running the VHF on the car's battery... then we know for a fact you are still getting noise from the fridge through the boat's wiring.

This is a major turning point before going after the radio itself. Make sure the antenna is disconnected and see if it makes any difference during this test.

Lemme know what you find out...

[Patrick]

OK, here are a couple of facts. 1) the VHF gets a loud humm when the 12v dc side of the frig is running. The humm cycles on and off as the frig cycles. 2) the vhf humms with and without the antenna pluged in. (again, only when the frig is running dc.)

I have not tried the seperate battery yet. I'll give that atry and let you know.

Thanks for your efforts.

Patrick

[SomeSailor]

Well... that narrows it down to the DC side of things. A separate battery will rule out the radio itself, then we'll be able to figure out where to go next.

[Patrick]

Just finnished the seperate battery test. Hooked 12v jumper wires from my pick up the vhf radio. Turned on radio & 12 frig. Nothing, NO HUMM, not even a hiss. Tried it with and without the antenna pluged in. No humm. So I guess that is good news.

Pluged the radio back into the boat 12v supply. HUMMMMMMMMMMMMMM!!! very loud.

so what should I try next?

Patrick

[SomeSailor]

There are a couple of approaches then. The good news is it's not your radio filtering or picking it up in the IF stages.

The diodes really should have dumped it to ground. Are you sure you got 0.1µF (micro-farad) 50V, non-polarized, ceramic capacitors?

They have to be non-polarized.

You could buy a noise suppressor at most radio shacks, but it sounds like your fridge has a pretty serious problem in the DC-DC power supply. Aside from wiring it separately from the source, you're going to have to either eliminate the source, or figure out a way to get it all to ground through caps and/or diodes.

[3788sam]

Had a similar experience with a stereo amp.(a cheap one at that) After trying everything to get the hum out, including adding a filter and running the wires back to the 12v bus bar. The only thing that worked was pulling a new set of leads direct from the battery. Cause of my hum was the battery charger which is hooked up through my panel.

[SomeSailor]

Yeah... if there's enough of it it's hard to get rid of. That might be the best way is to isolate that one circuit off the mains. Taking the radio back to the batt swicth directly might help.

[heymagic]

Reading back through this thread...I believe on a conventional 2 way fridge that it really only runs on 12 volt ?? The AC side is cut to 12 v at the fridge. If that is true then the only difference between AC and DC to the fridge is the source of the 12v ( battery, charger or built in converter ). The business end is the same. The battery only would provide the least amount of voltage and the AC converter the most...as a rule. So does it make noise on 12 volt with the charger off ? Does it make noise without the engine running ? If it only makes noise with the battery alone, no alternator or charger , then there must be a low voltage issue causing the motor to do something wierd. Can you tell I'm not an electrical engineer ?? :argh What is the actual 12v vlotage at the refer?Gene

[Patrick]

The package reads" MD.1 .1uf 50V Monolitithic Ceramic Capacitor, CAPACITORS".

You said add two to one location, Is that two together at one splice or two at two different splices? Or does it matter. I have only tried one at the vhf and one at the frig.

Best as I can tell the frig is the ONLY thing that causes the humm. With everything else shut off except the frig it will himm. No charger, alt , blowers or pumps cause the humm. Just the frig.

[SomeSailor]

The idea is to drop the AC (the noise) from the DC wires... before they get to your radio. You'll need one on each wire... and another between the two to cover all the possibilities.

1 - from pos to ground
1 - from neg to ground
1 - from pos to neg

They're caps, so they'll be invisible to DC. They only pass AC.

[Patrick]

I added the cap's just like you picture.One between Positive & Negitive leads behine vhf. And One between Positive and negitive 12v wires to frig.

Is Negitive and Ground the same wire? What do you mean by " Neg. to ground"?

I hope I'm not sounding stupid about this whole thing. But I ran out of options to try.

Patrick

[SomeSailor]

Usually just the one should catch all the spikes, but sometimes (like on RC plane motors) you need to connect all three.

When I say "ground" I mean the chassis of the fridge or radio. You might want to do all of this with scrap wire to see if you can get it to quiet down before wiring anything permanent.

Getting the radio wired directly to the OTHER battery might help, and you could try that as a temporary solution. There are basically two approaches. Isolating the noise from the rest of the boats DC, or isolating the radio from the rest of the boats DC. I think the latter will be easier.

Did Genes ideas help? I'm curious about the charger part he mentioned.

[Patrick]

Sorry for the delay.... My boat has been parked, and I have been buried at work. As for the vhf noise, I think I will try some shielded wire to the radio, and wire it directly to the battery switch. See if that helps. That will still be another week till I can get to it. Thanks for the help. I'll post again after I try it!

Patrick