Thread: Defender (Puma) radio interference

I have no idea but could only be the alternator, couldn't it? Had it full of mud?

Try a snubber on it, cap to ground and see if that helps.

Hi patto1

Before you start fitting noise suppression components on your vehicle, I would try and find the source of this noise.
A fairly easy way of doing this is, grab hold of a pocket AM radio ( that works ), then turn it off the stations into a quiet part of it's AM band .

Turn the volume up until you can just hear the hash noise in the radio then ease it back a little on the volume until its a bit quieter.
With this set, start the Land Rover and turning around the radio about itself you will find that the noise the Land Rover makes in the radio will vary in strength, walking around the vehicle you can then use this effect to pin point the nosiest parts, if the noise coming from the radio is too loud, reduce the radios volume until it is usable and continue working.

Take particular note whether it is the wires, for example: that are leading into a computer or the say, wiring feeding the injectors.
Other noise sources can be voltage regulators or the alternator, etc.

Let us know asap on this thread then we may be able to offer some suggestions as to how to help.
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This is not unique to the Puma as my Td5 causes the same interference with the HF. I believe other electronically controlled diesels do similar things

If you haven't found the source yet, maybe try this.....

Long story-made short, a patient I worked with, worked as a profession doing just this, finding and repairing the interference grounding issues on vehichles. By chance he mentioned that they usually started with the exhaust system. Since the exhaust system is attached by rubber (insulation) hangers in all places except where it runs from the exhaust manifold, it can actually act as an extra antenna. They would ground the tailpipe back to the chassis with a small piece of wire to see if that stops it.

Hope this helps, I'm just the messenger.

Hi All

I agree with the grounding of panels to quieten RFI ( radio frequency interference ) especially the bonnet or doors.

Using capacitors, ( they stop direct currents and pass alternating currents, ) are sometimes a better way to go, I say this, as earthing a exhaust pipe to the chassis using a earth strap, could cause some weird fault, if the vehicle's earth bond between the chassis and motor was to come a bit resistive in it's joints.

I have seen RFI in a ( EFI ? not sure if this is the correct description for this truck ) Mack truck become worse when they tried to quieten the RFI.
I didn't agree at all with the other technicians 'fix', He desensitised the VHF two way radio by internally adjusting the squelch setting, this reduced it's range considerably!
Shielding wrapped around the wiring loam and then grounded at the best distance from the noise source would have been the best solution to this RFI problem.
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Shielding wrapped around the wiring loam

For peat's sake, that's very earthy . . . sorry, spellcheck off . . . anyway, I've read a lot about this over the years, but do you know - radio types never really explain anything!

So what would you use as shielding? For instance, if I started shielding my distributor-to-coil wiring, (the low tension wires, that is), what would be the best stuff to use?

And what would you use as a capacitor? I notice the one next to the electric fuel pump on my carbie Rangie looks a lot like the condensor from a points distributor. Would a condensor, (easy to buy and cheap), do the job or is it more specialised than that?

And something else I read the other day said that braided copper is best for grounding body panels as the RFI travels on the outside of a cable. Is this right? And it sounds like ideally you need one of these straps for every door and the bonnet of a vehicle?

(And pardon the partial hijack, though it is on topic at least.)

This may give some ideas

Common rail diesel* Interference suppression

Martyn

Hi Martyn

I have just seen your posting. That is a well thought out explanation of how to systematically work the problem of RFI.
I had already drafted this posting but had a lot to delete and add still so I hope no one takes an exception as I didn't have time to rework it.
Here is my post anyway.

Originally Posted by Davo

For peat's sake, that's very earthy . . . sorry, spellcheck off . . . anyway, I've read a lot about this over the years, but do you know - radio types never really explain anything!

Hi Davo

I wonder sometimes if the best way is not to explain ????

For instance, how do you explain the damage to coax I have seen, that was caused by a lighting strike?
The coax was cut into 2 metre lengths between the TV aerial and the house !
The reason this damage was caused in the first place was the lack of a suitable earth and lightning rod at the aerial mast.

How to explain the couple of dozen cuts caused by the intense heat ( think, lots of power in Mega Watts ), can also be used to think about where the earthing on vehicle shielding should be.
The distance between the cuts in the coax is the clue and knowing that duration or pulse of a bolt of a lightning only exists for a certain time, sets up what is called a standing wave. But I am not going to write up a thesis on standing waves from Lightning strike, from a four year course at university and post it here on this forum. So for those that what to know more, I suggest that you read up in theory books designed for training radio technicians.

So what would you use as shielding? For instance, if I started shielding my distributor-to-coil wiring, (the low tension wires, that is), what would be the best stuff to use?

Is it the low tension wire the one that is causing you trouble?
If you need to, I would use what ever is at hand, if you work for a multinational manufacturing plant, the job would get exactly what is required. Out in the scrub you could try stripping the inner out of some large coax and use the sheath and the braid sliding that over the wire radiating the electrical noise. A bit of knowledge of antenna theory is also handy at this point, so the earth can then be attached to the improvised shield, where it would be the most effective.

And what would you use as a capacitor? I notice the one next to the electric fuel pump on my carbie Rangie looks a lot like the condensor from a points distributor. Would a condensor, (easy to buy and cheap), do the job or is it more specialised than that?

have a look for a impedance chart for capacitors and choose the size from that. you will need to know the frequency band that the noise is a problem in. A previous posting I did warn not to try adding on capacitors haphazardly on, especially electronic devices such as car computers that have pulsed information on those wires.

And something else I read the other day said that braided copper is best for grounding body panels And it sounds like ideally you need one of these straps for every door and the bonnet of a vehicle?

Yes, try a clip lead first and if it does make an improvement then go to something like those grounding straps for the mechanically longer life they can deliver and do try one panel at a time.

RFI travels on the outside of a cable. Is this right?

As a rule of thumb, HF travels through the conductor and signals in the UHF range travel on the surface of a transmission line or aerial element.

(And pardon the partial hijack, though it is on topic at least.)

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