RF Interferencec

[timchapman]

Has anyone any knowledge or experience of fitting ferrite cores to power and RF cables to reduce interference. My Raymarine echosounder and Autopilot course computer generate a lot of noise on my radio, particularly longwave. I also suspect my E series and GPS do the same.

Is there a difference between ferrite cores, can you cause any harm/degradation by using the wrong one?

 

[Benbow]

Is there a difference between ferrite cores

Not really, just depends how thick the cable is that you are trying to thread round.

can you cause any harm/degradation by using the wrong one?

No.

Try these

from here

 

[savageseadog]

They are more effective if you put several turns round the ferrite instead of just passing the cable straight through, twice round = twice as effective. Put them as close to the unit that you are trying to protect/suppress as you can. It's also much more effective if both power cables are put through or round the same ferrite together.

 

[Benbow]

Indeed, get as many turns as you can. But ideally leave a gap between the in and outgoing wire to prevent direct coupling. Like this:

Sorry about terrible picture!
This is the same ferrite as I mentioned above.

 

[William_H]

Old computers are an excellent source of ferrite rings. Especially in the power supply and on the main board. Although you can buy them from usual electronic suppliers.
The ferrite increases the inductance of the cable. So more turns the better until the resistance of the wire starts dissipating power to your set. You can ether wrap the actual input wire around the ferrite or cut the wire and insert a heavy wire coil from a computer. Usually just the +ve wire needs it but -ve as well is ok and possibly necessary.
ferrite is however only one approach to interference problem and may or may not fix the problem. The ferrite is designed to stop interference coming along the power or other control cabes. Either going into the set or radiating from it.

It is probably woth adding a bypass capacitor to the power cable near the set. Again these can come from an old cop[uter power supply or mother board. They need to have a voltage rating more than 12 volts. (almost all fit this criteria) The larger tubular (often black) capacitors are "electrolytic" capacitors and have very large capacitance. (like 100ufd) (100 microfarads) . This large capacitance really smooths out large variations in power supply either from the sets demands or from variations coming in. However because of the convoluted construction of the capacitor they exhibit inductance them selves which means they are not so good at very fast changes. You need to fit in paralell a small ceramic capacitor of a valure about 1000 uufd 1000 picofarads. Anything from 100 to 100000 will do as long as it is physically tiny. Connect both capacitors in paralell and to a good earth ie the body of the set.

Interference is a process of doing different tricks until the problem is solved. You can easily isolate if it is interference coming on the power line by temporarily powering from a separate battery with short leads. If this fixes the problem then go the ferrite and capacitor route. Ferrite first thenm capacitor. Do this treatment on first the causing set then the receiving set.
If these fail then you might have to consider phyically separating the sets.
You may also need top add ferrites to cables to indicators etc. However don't put the capacitors on anything but battery feed wires.

olewill

 

[timchapman]

Excellent advice from all, thanks. I'll report back with results