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MG MGF Technical - Did Mobile phone cause this problem??

Today my car was parked all day at work, every hour or so i heard an alarm which sounded like my MGF, i looked out of the window and the lights were not flashing, so i assumed it was not my car. The alarm only sounded for about 30 seconds, so i didn't have time to get to it before it stopped.
When i got home today, after it had been parked outside my house i heard the alarm again, so this time i went to check it but by the time i had got outside it had stopped. So i checked it over for open windows or doors ajar etc, but nothing seemed wrong with it. Then i realised that i had left my orange mobile phone in the car all day.
Could this be setting off my alarm somehow?
I have removed the phone and it hasn't gone off for the past hour!! (keeping my fingers crossed), has anyone else had this problem? or should i be looking for something else?
Mike

We have the same problem. Took several false alarms to realise the problem.
It appears to be only the orange network which sets it off.
Graham

Thanks for confirming this Graham, i wonder if it only affects MGF's? Has anyone experienced the same problem with any other cars?
Mike

Conversley, I leave my mobile (Orange)in the car sometimes and the alarm doen't go off. So even if it is a 'problem' it surely must be the settings on the alarm - sensitivity?
Chris


Hi all,
a bit technical but here is the reason for the alarm to go off; The alarm itself is a 2,4GHz doppler module of very high sensitivity. Normally such a module would only be affected by a phone having a Blue Tooth /Wireless LAN -module. So an ordinary mobile phone should NOT make the alarm go off... But as usual there is a small thing that makes this happen and that is bad (or nearly non-existing) de-coupling of the attached cables to the alarm. Unfortunatly the cables feeding the alarm and giving signals back to the main unit is so badly screened/de-coupled that this is the point where the "roaming" signal from the mobile phone enters and sets of the alarm !
I had an old alarm unit in the lab for measurements as well as I took it apart just to find out why it was so sensitive to out of band signals. The cure for this is to put some ferrite beads on the cables before they enter the unit. After this modification only signals entering the correct way thru the slot antenna at the front of the unit will trigger the alarm ...
Funny that this hasnīt been corrected on newer cars as this must be a known problem .

Regards , Carl.
Carl

I believe you have to double-lock the car, activating the volumetric sensor, for the phone thing to cause problems. This is a vague memory of others' posts from the past though, as I've never encountered the problem.

E
Ed Clarke

It is not just Orange phones that do this - I've left my One2One phone in the car one evening, and was alarmed (oops, sorry, no pun intended) to hear that the alarm was being tripped once about every hour... It was only when I realised that I didn't have my phone in my pocket did I realise what was happening!

Carl, a quick - and very naive - question about the ferrite bead mod of yours. Are we talking about steel ball bearings here or something more sophisticated???

Cheers
Rob Bell


Hi Rob,
the ferrite beads are commonly avaible at any electronic parts supplyer. Farnell have them as "tubular cable shields" or EMI sleeve for a few p each. Also the "hinged clamp cores" are very effective but a bit more expensive at around 2 pounds each. One of these will clamp over the cables and should be set as close to the alarm unit as possible.You will probably see similare thingies at the cable ends of computer hardware as USB cables ,monitors etc. Might do some pictures etc. when autum comes and send to Dieter for his site. IMO this should have been done at the assembly of the unit at really no cost at all...
BUT,this modification is fine for out of band signals as normal mobile phones etc. but will NOT stop any inteference comming in the "legal" way via the alarm units antenna. And here we have a variety of sources as nearby microwave owens, Blue-Tooth, Wireless LAN etc. And they do get more and more gadgets into this 2,4 GHz band by the day !!
So a freq. band that was almost totally free from inteference in the early 90's when the "F" was developed is really cramped with all kind of interfering sources today !
The old ultrasonic alarm system wasnīt that bad after all... Only that the visible transducers in the dash collected dust and was difficult to clean ;)

Regards , Carl.
Carl

This thread was discussed between 27/05/2002 and 28/05/2002

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