The noise is driving me mad

[john_travers]

VHF on. Engine off. Instruments off. No noise on the VHF.
Engine off. Instruments on. No noise straight away but over time noise occurs to the point where the squelch control has to be turned so high it effectively suppresses all signals. Noise worst on Ch16.
Engine on. Instruments on. Same problem but worse!
Previous threads mention direct connection of VHF to battery and use of ferrites.
What is a ferrite and where do you put it?


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[bedouin]

What sort of "noise" are you experiencing?

A ferrite is a device that is clamped round a lead, making it into an inductor. This helps prevent high frequency signals being transmitted into the equipment along the wires.

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[Birdseye]

I suppose that its stating the obvious to say you are getting interference from the instruments and engine.

Could be any of three problems - the radio, the aerial, or the power feed. Try a process of elimination. If you can get your hands on somebodies emergency vhf aerial, connect that up and see if that makes a difference. If it does, then you have isolated the problem to the aerial. See if you can borrow someone elses radio and plug that in - if that works, then you have a radio problem / weakness. Finally, try lugging a seperate 12 v battery on boardand connecting that to the vhf only.

If it is the aerial, then the first step is to make sure the aerial connections for the co ax braid are good. Do you have an anenometer? If you do, does switching that off make a difference? ie is there a problem with parallel cable runs up the mast? Aerials dont last forever, and if there is no obvious problem at the connectors, I would simply replace the aerial.

Turning to the power supply, again the first check is the connections, not just at the radio but going right back to the battery ie inc any in line fuses. Assuming these are good, then try some ferrites. These are simply little tubes of iron oxide and resin which turn the feed wires into an inductor making it more difficult for alt current to pass along the wires. You can buy them very cheaply at Maplins, where they are sold for reducing TV interference. You just clip them round the power supply wires, and you can put them round the aerial coax too.

If its the radio, then its off to the repairer to get that tested.



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[poggy]

Hi,

As it takes some time for the noise to appear, it could also be the instruments that could be at fault. Heating of components can cause this problem so as the instruments are left to "warm" up the noise is caused. The other alternative is that this is normal behaviour for the instruments, but the radio has a fault which prevents it from filtering it.

The ferrites are good if you believe it is a problem from the power source, but if it is a radiated problem from the instruments they will not normally help as you can't put them on the aerial. If you do use ferrites use them closer to the radio end then the battery, but in all honesty it will be masking a problem as you shouldn't need them.

If you have a hand held, does it suffer from the same problem if you put it in a similar position and if not try the 12V charging/adapter lead and see if it does it.

Good luck.

Poggy






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[webcraft]

My (new) McMurdo DSC VHF set makes a loud clicking on dual watch as it switches from one frequency to the other. Previous (non-DSC) VHFs I have used have either not done this or I have not noticed it. Does anyone else get a clicking like this on dual watch?

- Nick


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[david_bagshaw]

Sounds as if it might be the voltage stabalising circuits in your Instruments is poor or failing, as this often gives out a squealk of its own. Have a similar problem if the hand held vhf is left near the handheld garmin, only when the garmin screen has its light on.

would definately try the use a seperate battery / supply as suggested earlier, otherwise it is something in the set it self.

<hr width=100% size=1>David
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