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interference on medium wave

Hi, ford mondeo 1998, mk2 with fitted radio. Previously had a tomtom pda and bluetooth gps navigation device, mounted on the windshield and charged by the cig lighter. Cable would come from the lighter to the mount (pda would sit in the mount and be charged) and the tomtom would be charged off a cable coming from the mount.

This generally worked ok. I like to listen to bbcr5 (693mhz) and talk sport (1071mhz). What i found was bbcr5 performed fine, but I would get some slight interference on talksport when the pda was switched on.

I have just bought a new pda which is a phone plus pda(xda exec), I have fitted a mount for this, the power cable is a single cable coming from the lighter, which (y) splits into two, one cable plugs into the pda the other into the tomtom gps reciever.

I now find intolerable interference on the medium wave. If the tomtom reciever is on, and the pda is on, no problem, however, if the tomtom reciever charger is plugged in, i get a high level of hiss, and if the pda is plugged in i get nothing more then high pitch whinning noises through the radio. Sometimes the noise can reduce and the radio is listenable, but mostly not.

I have tried repositioning the cables, it makes no difference.

Question is, does it sound like the charger cable itself is poorly insulated, and thats why I am getting the interference? If so, I am having trouble locating an alternative cable, would wrapping the cable in insulation tape or any other material reduce the interference??

thanks

Gaz

Reply to
Gaz
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No. Insulation tape won't shield interference otherwise radios with plastic cases wouldn't work. What you need is to screen the cable. You could try some aluminium tape especially if you attach a ground wire to the tape and earth it to the car.

Reply to
Malc

Thanks for the advice. Normally charger cables arent earthed though, are they?

You reckon this would sort the problem out?

Gaz

Reply to
Gaz

I have some silver coloured duck tape, would that contain aluminium?

Gaz

Reply to
Gaz

I get this interference now in my Mk3 Golf and I dont have a PDA or GPS running. If anyone knows what causes this please let me know. Years ago, I had the same sort of thing on a Mini and it seemed to originate from the voltage regular device that powered the fuel gauge. The car is now about 5 or 6 years old and it never did this when new for the first couple of years. It sounds like an interfering signal, that heterodynes with the 909 or 693 signals. Turning on the heated rear window or headlights sometimes shifts it for a bit, then it drifts back. VHF reception is good - thank goodness. I believe VW's have an inline aerial amp somewhere could this faullty and dropping the signal strenght? I've never found out if I have one or where it is located yet.

Reply to
Peter

The trouble with some high frequency interference, is that it is carried down the cable, try getting a ferrite ring and putting a coil thru a ferrite ring, if you have less/no problem on FM check the radio aerial earth, If you have the radio on an am station and touch the aerial, if the signal gets dramatically better you have a problem with the aerial! What you need is the radio signal to be stronger than the interference!!! and I don't think your ducktape will help, sorry.....

I have a similar problem with my GPS unit but it doesn't become unbearable till I have a weak signal on AM, which to be honest when FM fades out it's just when I need it!!

Most electronic equipment puts out RF interference but most car radios are made to a price and that price doesn't include rf surpression.. Many years ago my first laptop was an amstrad PPC it had come from the swedish market and was totally screened, the UK versions weren't!!

Des

Reply to
Des

Possibly if it's running of the car as one side may be connected to the -ve on the battery. What I'm proposing is an extra layer of screening around the cable and maybe the charger (leaving vents open).

It's worth a go as it'll only cost a small amount. Also what Des said is good advice too. Add a couple of ferrite beads and maybe a suppression capacitor.

Reply to
Malc

Use a pocket transistor radio to hunt down the source of the interference. Hover it in the engine bay, the bulkhead, and in your case, also along the fuel line to the tank. You might strike lucky!

I have no recollection of doing anything to the fuel gauge or the pump in my Mini (a van it was, so a good booming base!). The rudimentary AM radio, a

3" dial affair placed on top of the shelf with an extensible manual aerial in the wing (through an ugly 1" drilled hole) eventually worked OK without interference, as I recall.
Reply to
Lin Chung

Does that car have the radion antennae built into the windscreen? If it does, you'll probably find it immpossible to remove the interference without installing an external aerial.

JOhn

Reply to
John

But the problem is entirely down to the charger cable, which is essentially, a cig lighter adaptor to a miniusb, and a tomtom connecter. The charger cable is poorly made.

If I use another solution (to clumsy to be permanent, but shows it works), such as an arkon powered mount, it delivers the same power, to both the xda exec pda and the tomtom, with no such interference.

I am going to try out the ferrite ring solution tomorrow...............

gaz

Reply to
Gaz

You didn't answer my question. Is the aerial built into the windscreen. If it is and its transmitting interference all around the dash then you'll find it very hard to eliminate. I've a lot of experience with problems like this going back to the days before FM was common and if the interference is being picked up through the aerial you won't eliminate it. Depending on how fussy you are you might get it to an acceptabe level.

John

Reply to
John

Dont think so, it is mounted on the roof of the car.

If

Uhm, as I said, I ahve all kinds of electrical gizmos in the car, different trackers etc, it is only this one charger cable which causes this big problem. I tried the suggestion with the ferrite rings, even tried two in succession, didnt make a jot of difference......

Gaz

Reply to
Gaz

If it's just a straight power cable it can't generate any interference.. There must be some switching device that drops the voltage. What is the input voltage for the two devices. If the charger is switching at a frequency that is being picked up by the radio then putting ferrite rings on it won't make any difference.

JOhn

Reply to
John

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