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Radio White Noise after 20 minutes

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Post by pads Tue Sep 27, 2022 3:07 am

We have a problem with our radio whilst driving. The m/h is an AutoSleeper Broadway Duo 2016, but I think it is a FIAT issue Ducatto automatic).
It has been there since day one, but FIAT & AutoSleeper have blamed each other, and now I am fed up and need a solution.

The problem -

After about 20-30 minutes driving, the radio signal (FM and DAB) starts to develop 'white noise' which increases quickly to a level where listening is impossible.

This does not affect music played from my iPod through the 'radio'.

So what have I tried -

  • Turned the radio off and on - noise still there.
  • Pulled in and turned vehicle engine off (key out) and back on again (not started) - noise still there.
  • Changed the aerials FM & DAB to screen ones - noise still there.
  • Replaced the radio (on a temporary basis) with a JVC one (from previous vehicle) - noise still there.
  • fitted noise supressor to radio feed - no change
  • fitted ferrite filters to vehicle and leisure battery feeds - no change.


It does not happen when parked up and listening to radio (engine obviously off)

The problem only goes if the vehicle engine has been stopped for some time.

Any suggestions would be appreciated

Peter
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Post by v8oholic Tue Sep 27, 2022 7:58 am

It seems like you've covered all the obvious areas. The only things that spring to mind are if the radio output goes into a separate amplifier before going to the speakers, and it has a fault. Or perhaps, assuming that when you tried a different radio and the same thing happened you used all the same wiring, maybe the radio's earth connection is imperfect and failing once it heats up.
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Post by FreelanderUK Tue Sep 27, 2022 10:19 am

Try fitting a different earth wire, as mentioned by v8oholic some radios have a separate amp which could have a dry joint in the solder and as warms breaks the contact,  you could also try just plugging in the speakers to the radio and use a new live and earth feed straight to the battery

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Post by pads Tue Sep 27, 2022 5:02 pm

Thanks for your thoughts.
Just to say there is no seperate amplifier.
So as you say it could be the earth connection.
I'll try a seperate earth connection.
Peter
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Post by babian Wed Sep 28, 2022 7:04 am

Have you taken a portable FM , Dab radio with you (battery operated) ?
This would allow you to use  that to see if the vehicle/habitation area was causing an interference (bad relay , warm contact etc) with the radio signal/reception. 
When the head unit starts doing its "thing", turn it's volume down then turn on the portable battery one to listen if that's clear or not.
As you have said radio head unit is OK if engine not running.
Tracking the wiring fault could be long winded. Am I correct in thinking in the old days if a car had a bad ignition fault , contact breakers etc, as it passed your  house, the radio went funny and the old b/w TV ?

Good luck with your problem here
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Post by rgermain Wed Sep 28, 2022 8:37 am

Sorry cannot help, have never tried to turn our radio on after 6.5 years. Same in the car, never listen to radio when driving, well since I was a teenager.

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Post by FreelanderUK Wed Sep 28, 2022 8:56 am

rgermain wrote:Sorry cannot help, have never tried to turn our radio on after 6.5 years. Same in the car, never listen to radio when driving, well since I was a teenager.

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You don’t know what your missing , arguing with some of the people who call in on Radio 2 Jeremy Vine show and they can’t even hear you 🤣🤣🤣🤣

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Post by rgermain Wed Sep 28, 2022 9:55 am

FreelanderUK wrote:
rgermain wrote:Sorry cannot help, have never tried to turn our radio on after 6.5 years. Same in the car, never listen to radio when driving, well since I was a teenager.

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You don’t know what your missing , arguing with some of the people who call in on Radio 2 Jeremy Vine show and they can’t even hear you 🤣🤣🤣🤣
I would never listen to Jeremy Vine since he took the cyclist stance, anyway what is Radio 2, Gold Radio is the only one for me.
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Post by Peter Brown Fri Oct 07, 2022 2:36 pm

pads wrote:Thanks for your thoughts.
Just to say there is no seperate amplifier.
So as you say it could be the earth connection.
I'll try a seperate earth connection.
Peter

Sorry to come in late on this but we've been away.

Your description of the symptoms is comprehensive and facilitate an objective comment of the fault.

The problem only occurs after the engine has been running for some time and terminates after the engine has been off for a period of time. The delta in this circumstance is heat from the engine having effect on a component. The resistance of an electrical conductor increases with heat; if you have a poor connection in the 12v supply OR chassis connection to the radio that is located in the proximity of the engine generated heat then as it warms up the supply voltage to the radio will be reduced possibly to a level where the radio is still operating but the selectivity (ability to tune into a specific frequency) will be impaired.

On your particular vehicle I can't think of a component/connection in the 12v supply that would be under influence of engine heat so would start by looking at the bonding from the engine to the chassis.

It will be nice to hear how you get (got) on.
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Post by pads Fri Oct 07, 2022 3:11 pm

Thank you Peter for that information.
I have not had chance to do anything about it since we were last away.
However I will try a seperate ground to the radio. I assume that I should diconnect the existing ground cable to prevent 'earth loops'.

Thank you
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Post by Peter Brown Fri Oct 07, 2022 3:19 pm

Sounds like you know what you are doing pads. You will probably have chassis connections via the supply, aerial and physical installation, chassis connections to the engine block are most likely the cause as that is where it will be hottest.
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Post by Eltel Sat Oct 08, 2022 11:12 pm

As a matter of interest does it happed when you are using a usb socket for charging a device ?
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Post by pads Sun Oct 09, 2022 12:58 am

In reply to the USB question. I nearly always have the sat-nav plugged into a USB port. So it would be on from the start of the journey.

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Post by Roopert Sun Oct 09, 2022 10:54 am

If you haven't already tried, I would definitely try unplugging that once the noise starts. One possible mechanism is that the satnav's internal batteries are charging for the first 20 mins or so, and then the charging mode changes when the battery is fully charged.

Similarly, if you plug in phones to charge while driving, the chargers used for that can also be very electrically noisy.
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Post by pads Tue Nov 01, 2022 12:57 pm

Thank you Roopert

We have just had a chance to test your suggestion (been away for a few days)

It turned out to be the satnav charging system. I unplugged the satnav at the device end (not vehicle) and the noise stopped. Checked a few times to ensure it was not coincidence.

I tried putting a couple of ferrite cores on the feed cable, but this has not helped.

Do you have any suggestions - other than replace the satnav!

Thank you
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Post by Roopert Tue Nov 01, 2022 6:07 pm

It will depend on the make/model, but typically in that situation the problem will be with the 12V -> 5V converter that is (usually) built into the USB socket. These are built down to the lowest possible cost, and typically the first "unnecessary" components that the manufacturers decide to discard are those that limit EMI (which is what you are hearing).

Most big-name satnavs are very carefully designed with respect to EMI - not least because the satnav is trying to pick up extremely low-level radio signals from a long, long way away.

So, I would try replacing the 12V -> USB converter first.
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