FM radio interference

snipez999 · Post by **snipez999** » Tue Jan 24, 2012 11:12 pm

So I have the BMW Individual audio and DAB radio upgrades but still find that switching the rear demister on causes radio interference when it is receiving an FM signal (ie. when the DAB autoswitches or when you are listening to 'pure' FM).
Took it in to dealer, said nothing wrong. I insisted, citing said upgrades. They re-booked car and got senior engineer to take a look. result is one replacement rear screen on warranty.
Google tells me this was a problem for the E46 too. Lessons not learned then.....

X5Sport · Post by **X5Sport** » Wed Jan 25, 2012 1:01 pm

Mixing RF (AC) signals and DC on the same wiring is often problematic and I suspect that the isolation circuit or filter wasn't working as well as it should have been. You can also get bad elements on the network that cause some problems. It will be an issue for any manufacturer trying to run RF and DC on identical wiring.

The Dealer really should have just changed either the screen or the filtering circuitry rather than walked away - or tried to.

When I was working on covert police vehicles thirty years ago, keeping the on board domestic and police comms systems apart was tricky, add in the need to keep the rear screen functioning too and we used to have some real challenges. The heater DC could fry the radios and the high power RF could fry the domestic kit. We took great pride in being able to turn just about anything into an aerial. A clever piece of circuitry called a multiport isolator did the trick, but a change in the electronic performance of any one of the items would change the 'reactance' of the whole network and it could all need resetting or rebuilding.

Rusty · Post by **Rusty** » Wed Jan 25, 2012 8:00 pm

[quote=""X5Sport""]Mixing RF (AC) signals and DC on the same wiring is often problematic and I suspect that the isolation circuit or filter wasn't working as well as it should have been. You can also get bad elements on the network that cause some problems. It will be an issue for any manufacturer trying to run RF and DC on identical wiring.

The Dealer really should have just changed either the screen or the filtering circuitry rather than walked away - or tried to.

When I was working on covert police vehicles thirty years ago, keeping the on board domestic and police comms systems apart was tricky, add in the need to keep the rear screen functioning too and we used to have some real challenges. The heater DC could fry the radios and the high power RF could fry the domestic kit. We took great pride in being able to turn just about anything into an aerial. A clever piece of circuitry called a multiport isolator did the trick, but a change in the electronic performance of any one of the items would change the 'reactance' of the whole network and it could all need resetting or rebuilding.[/quote]

Bloody Hell Harry (as my boys like to quote from Harry Potter)
All sounds a bit technical to me

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X5Sport · Post by **X5Sport** » Wed Jan 25, 2012 8:35 pm

You're not wrong! Sometimes VERY technical.

snipez999 · Post by **snipez999** » Wed Jan 25, 2012 10:49 pm

Booked in for later in Feb due to work schedules.

Have also got a replacement set of BMW Performance rear window fins sorted FOC for if they cannot re-use the existing ones (which I had bonded on after the shitty original glue stuff failed)

snipez999 · Post by **snipez999** » Fri Feb 24, 2012 8:56 pm

All sorted, new rear window and performance fins fitted FOC as anticipated. Result

X5Sport · Post by **X5Sport** » Sat Feb 25, 2012 10:49 am

Glad you finally got it sorted.....

Does that mean avoiding the non-OEM fins that are about these days too? How do they affect the airflow over the rear screen when clearing water whilst driving? I still don't know why there is no rear wiper on the X6, as it could do with one!

snipez999 · Post by **snipez999** » Sat Feb 25, 2012 3:25 pm

I got on fine with my Chinese ones, but the originals do seem slightly higher-sided. They do actually help to aid airflow across the rear window as you can clearly see the slipstreaming effect when driving. They do a great job, along with my ACS whalefin and Hamann rooftop spoilers, of taking away the dreadful pillbox looking back end of the car.

Will probably go with another similar set up on my M50d or 6M. I have decided to trial them back to back to see which I fancy. Roll on June... Though Marrakech brown exterior with cream interior might be too much of an acquired taste?!?

X5Sport · Post by **X5Sport** » Sat Feb 25, 2012 3:49 pm

Thanks for that. Must admit that I'm not sure about that metallic brown either - but only seen pictures and not a real one!!

Be a while before an updated version appears in my garage now though. Too much going on at home and work. Not driven since Xmas and won't get the OK until after the major neck surgery in three weeks time to solve this left arm nerve problem caused by a failed disk, and if all the post-op tests come back as OK a month after. Not looking forward to it, but it does need sorting out so no real choice...

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