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white noise
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recoil
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Joined: Sep 26, 2005
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PostPosted: Fri Oct 28, 2005 6:35 pm    Post subject: white noise Reply with quote

I have a HP Ipaq RX3715, I have got tomtom5 on it, and a 1gb SD card. Playing MP3's and tomtom is not a problem but for the GPS reciver to work it has to be plugged into the fag lighter. As soon as I plug it in the the fag lighter I get a very high pitch screech
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mikealder
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PostPosted: Sat Oct 29, 2005 1:38 pm    Post subject: Reply with quote

Does it wine with the engine off? if it only does this with the engine running then it probably a faulty supression unit on the alternator, it could be elsewhere, ignition etc. As another test try the set-up in a mates car - does it behave the same way then? - Mike
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Gerco
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Joined: Nov 22, 2004
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PostPosted: Sat Oct 29, 2005 2:08 pm    Post subject: Reply with quote

This kind of noise mostly produced by the switched power supply.
Mostly no chance to avoid/repair/alter.
Poor PCB design and no or wrong shielding.
Please ask supplier for replacement.
A friend of mine did like this and ... the second one was poorer than first one.
Third one was better, but still noisy.

Good luck

Gerco
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recoil
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PostPosted: Sat Oct 29, 2005 3:15 pm    Post subject: Reply with quote

It does it with engin off aswell, would it be the fag lighter part thats not good, or the cradle.

if its the fag lighter part would hard wiring it in and not using the fag socket make a difference
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mikealder
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PostPosted: Sat Oct 29, 2005 5:41 pm    Post subject: Reply with quote

As it does it with the engine off it must be the addaptor you are using to power the PDA, try another one get one that is capable of at least 850mA - the noise will be caused by the regulator chip in the plug - Cheers Mike
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recoil
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PostPosted: Sat Oct 29, 2005 8:23 pm    Post subject: Reply with quote

thx for your replies, I have just tryed again, plugged it into car stereo and screeches, remove from fag lighter fine.

tryed it with headphones, ablosutle fine using the same cradle and adapter

So I dont think it can be the adapter, the wife said could it be that the fag lighter and stereo are drawing power from the same circuit (dunno if they do just a thought)
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mikealder
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PostPosted: Sat Oct 29, 2005 10:10 pm    Post subject: Reply with quote

It could be RF emmisions from the PDA that are interfering with the radio, or are you playing the audio from the pda through the car radio via a transmitter? - try moving the PDA further away from the radio set if this improves the situation then its the PDA emitting RF noise (probably from the screen PSU) - Mike
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Gerco
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PostPosted: Sat Oct 29, 2005 10:43 pm    Post subject: Reply with quote

This RF noise is coupled into the environment AND into the cable.
So placing the power supply further will not help.
You need to open the supply and add one coil (L/C pi filter) EACH, in every cable, this will only remove/stop the coupling into the cable from the PCB.
This will NOT eleminated the coupling of the RF noise behind.
The stray field you cannot change/alter/remove.
The best fing is to replace the power supply by a DIFFERENT manufacturer.

Gerco
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recoil
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PostPosted: Sun Oct 30, 2005 12:01 am    Post subject: Reply with quote

Gerco wrote:
This RF noise is coupled into the environment AND into the cable.
So placing the power supply further will not help.
You need to open the supply and add one coil (L/C pi filter) EACH, in every cable, this will only remove/stop the coupling into the cable from the PCB.
This will NOT eleminated the coupling of the RF noise behind.
The stray field you cannot change/alter/remove.
The best fing is to replace the power supply by a DIFFERENT manufacturer.

Gerco


I understand what your saying, but I dont understand why, the Ipaq is in the cradle and conected to the car stereo witout the fag lighter and it plays fine, pluf the fag lighter in and it schreeches.

But when I tryed a pair of headphones there was no scheeching, even with the stereo turned on.

I dont understand how RF would have anything to do with it, surley if it was RF the noise would be there even with headphones on
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Dilemma
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PostPosted: Sun Oct 30, 2005 12:17 am    Post subject: Reply with quote

How is the PDA connected to the car stereo?
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recoil
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PostPosted: Sun Oct 30, 2005 12:29 am    Post subject: Reply with quote

I have a kenwood headunit, I got a wire from ebay that connects to the multichanger plug and gives you two phone inputs
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Dilemma
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PostPosted: Sun Oct 30, 2005 12:45 am    Post subject: Reply with quote

I presume that the head unit is mounted in the dash and you are using your PDA in place of the CD changer?

If so I very much suspect that you have an impedance problem, as the CD changer will be expecting a loaded circuit, whereas your PDA's jack plug will only be expecting standard unloaded headphone impedance.

I use one of the wireless transmitters (they have close peg type clip which fits around your PDA) and then reclaim your CD changer input. They work by tuning your stereo into a preset frequency, and the output of the PDA is then amplified and played through your car stereo. Have look on eBay, they go under the name of "car baby", and believe it or not only cost around a quid plus P&P.
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recoil
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PostPosted: Sun Oct 30, 2005 7:13 pm    Post subject: Reply with quote

OK new info, I tryed a new Ipaq coz the internal speaker had stopped working

I plugged it into the stereo and it was fine, plugged it into the fag lighter it was fine turned the engine over and it started to schreech, the screech was linked to the engine when I reved the pitch changed. I had the same prob ages ago, I installed an amp, I got the same noise where the pitch changed I didnt sort it our though I sold the car.

Someone must know the prob, it sounds like some kind of supressor.

Please someone help
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mikealder
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PostPosted: Sun Oct 30, 2005 8:32 pm    Post subject: Reply with quote

Recoil, you need a suppressor fitted to the alternator on the car, that is where the electrical noise is coming from - they are avail from Halfords or any good auto electrician, the alternator probably has one fitted but it may have broken, they let go after a while, alternatively you could fit a small capacitor across the fag lighter socket try part number SC87U only cost 34 pence from Maplin - Mike
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recoil
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PostPosted: Sun Oct 30, 2005 9:50 pm    Post subject: Reply with quote

call me stupid, but im assuming I put the cap in line with the power wire, or do you get two and put one in line with the earth, also I want to hardwire it in, so icould conect it to the adapter wires couldnt I?
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