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P38 Becm permanently 'awake', Tracking RF sources?


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Just spent  a couple  of hours yesterday and today going through both fuse boxes looking for a spurious current draw, as the battery seems recently short lived without the charger connected (vehicle sorned for Covid still), finally got the rear parcel shelf support off its clips and examined the RF receiver. To my surprise it is the first generation on a 2001 car, anyway.... unplugged the aerial and all is well. Current draw drops from about 0.55Amps to .03 or 4 when the Becm goes to sleep which I think is pretty normal.

I just wondered whether there is a (relatively cheap/simple) way to locate which RF and where from is the likely culprit? Any thoughts?

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I don't have any way of finding interference sources, but recalling reported experiences from 2 decades ago, culprits could be defined as 'any' domestic wireless apperatus, EXCLUDING WiFi and Bluetooth.
In the UK this leaves wireless doorbells, wireless baby alarms, wireless external weather stations (that reported to an internal base station), and remote garage door openers. Also indicted as 'electrically noisy' were wireless keyboards, used with PCs, and cash tills that reported overnight so stock could be reordered while the shop was closed. Railway stations on electrified lines were also a cause of problems, mainly for the very strong electrical signal cloud that occured when trains accelerated away from rest.
The cash tills and railway stations normally made their presence felt when a car was parked nearby but would not restart.
I understand wireless masts (not mobile phone masts) could also overwhelm the weak signal from a key fob, preventing the car from starting.

The other point of interest from when I changed my alarm receiver, after parking too close to Milton Keynes railway station, was that once out of the box I could not tell the difference between the old and new reciever. I did look specifically, but as I say, this would be around year 2000. The 'improved' receiver at that time was not listed in the parts list, that only had interim models, the very latest was only in the Technical Service Bulletin.

Regards.

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ISTR that one former member of this forum found that his house wifi was the source keeping his P38 awake at night, and that the receiver change was the fix.

If it's happening at home, flip the big switch on your house long enough to prove if it's something of yours, or your neighbours. If you know it's something of yours you can try invidual circuits, then individual items until you track it down.

But the if fix is going to be to change the receiver anyway, you might as well do that first.

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30 minutes ago, TSD said:

ISTR that one former member of this forum found that his house wifi was the source keeping his P38 awake at night, and that the receiver change was the fix. ...

Just look at the frequencies involved, both for domestic wireless items I've listed and the remote control keyfob.
Then compare them with the frequencies used for WiFi.

Wikipedia seems a resource with common standards, frequently peer reviewed.

Regards.

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6 hours ago, David Sparkes said:

I could not tell the difference between the old and new reciever.

Fairly straightforward now, some body I found on the tube had documented the differences, different colour stickers and when you open the box, the differences on the circuit board are immediately obvoius.

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We are fairly out in the sticks so some of the suggestions are less likely,... switching off the whole house seems drastic but would be a good start, also hadn't considered it but we do have a newish Aldi weather station, now that might get its batteries pulled for a it tomorrow as well. I suppose what was in my mind was a low cost spectrum analyser of some sort to direction find likely culprits but it makes sense to exclude the obvious and easy first. 

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I found that the BECM-equivalent [alarm/immobilizer] on my 90TD5 was being kept 'awake' by the thing-on-the-central-heating-oil-tank-that-reports-the-oil-level-to-the-display-in-the-house.

This was sending a reading every 10 minutes or so - and with my Defender parked only a few feet away it couldn't help but hear it!

The usual frequencies for the remotes are around 418, 433-434 or 868MHz. An old-style "Scanner" receiver (generally obsolete now the police/ambulance/fire-brigade have all gone digital) is a useful tool to investigate these kinds of problems.

I got round the problem by not replacing the battery on the in-tank sender bit and now just use the tank's external sight-gauge.

Edited by Tanuki
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