Radio Interference - how can I track down the source?

[London GT3]

About six weeks ago I started having trouble with operating our front gate with the clickers and opening/locking cars with the remote key fobs (not all cars but some worse than others). The gate clickers won't work unless they are right on top of the receiver. The car clickers are a bit mixed but many wont work unless they are right close up on the cars. Some don't work at all. Others work fine. Neighbours have reported problems locking cars in the vicinity.

I have renewed the batteries in all the gate clickers. The gate maintenance company has been out to the gate and they are baffled.

Something is interfering with the signals. I have isolated everything in my house so I know it doesn't emanate from there. There are lots of other houses around so I am guessing that one of them has installed something new that may be the cause. However, if I can't identify where it is coming from, I am at a loss to do anything about it.

Is there a piece of equipment that would be able to detect a strong radio signal in the area and give some idea of the direction from which it is coming?

Thanks.

[TonyRPH]

You would need an RF Spectrum Analyser (and a knowledgeable bod to drive it).

I live near an airport (about 2 miles as the crow flies) and although I've not had interference issues with car fobs etc. I do get a lot of static noise on the FM band.

However... If I park close to the airport - the car fob does become erratic (particularly with an Audi I once owned), and often won't work at all.

So do you live near an airport? (near enough for interference that is ~ 1 - 2 mile radius I'd say).

Incidentally - if it's something a neighbour has installed, I would be surprised - unless it's a really dodgy piece of kit that is transmitting constantly (rather than on demand as a key fob for example).

EDIT: fixed spelling.

Edited by TonyRPH on Monday 14th March 15:25

[nyt]

Common causes are airports (as above) or coastal radar installations.

Do you know what frequency the key fobs use?

Regarding detection: You could perhaps try a cheap software defined radio and a laptop (about 9 quid from amazon for the hardware, software free) and see if that gives you any clues - but without expensive directional equipment I think you're out of luck. But you'd need to know what frequency to look at and what the SDR covers.

How far is the nearest house? Is the interference there late at night. Cheaper LED transformers can sometimes interfere with *some* frequencies so checking at say 1am should eliminate those (and most other domestic sources) as a cause.


It does seem way more likely that it's a faulty connection caused by cold/damp than a new interference source.

Links for SDR:

http://www.amazon.co.uk/gp/product/B009VBUYA0?psc=...

http://www.rtl-sdr.com/about-rtl-sdr/

Edited by nyt on Monday 14th March 14:52

[steve_bmw]

If I park my car outside our local corner shop the keyfob won't lock the car, it's fine everywhere else.
They have 2 large satellite dishes on the roof, but I doubt it's anything to do with those?

[jjones]

Have you fitted a USB phone adapter to your car, these can piss about with noise into your cars wiring, not sure if this would be able to affect gate fobs though.

[Spare tyre]

Any 2.4ghz tv senders in the house?

Any new wifi?

[London GT3]

I'll disconnect all the WiFi at the weekend but I don't think that is the problem. I have switched everything off at the mains and the cars still won't lock/unlock.

[megaphone]

Anyone had any wireless CCTV fitted? As above video senders on 2.4Ghz or 5Ghz can be a PITA.

[Zad]

It will probably be a 433 MHz, unlicensed ISM (Industrial, Scientific, Medical) band system. That basically gets used by every cheap bit of radio controlled gear around. I have known old satellite dishes go faulty and the LNA mounted in front of the dish starts to oscillate. Close enough and "loud" enough to cause problems with car locking, alarms and all sorts of stuff.

Ideally you need a radio scanner and directional antenna. As mentioned above though, SDR radio receivers can be had cheaply, if you don't mind the faff.

[Andehh]

Just to add here, my flat mate's vauxhall astra's remote central locking was 100% blocked by my marmatek ir remote sender pyramids. Basically a device which let me use my sky remote upstairs to control the sky box downstairs, as the sky box was split between both tvs.

Never woulda guessed it myself, and it took us ages to track down why his remote fob only failed when parked on our driveway. Both must have used a very similar frequency, and the plugged in marmatek pyramid just drowned that frequency out in a 20m radius.

[TonyRPH]

As above - the key fob most likely operates on 433Mhz (LPD433) - Wikipedia article about this here.

WikiPedia said:

There is significant scope for interference however, both on frequency and on adjacent frequencies, as the band is far from free. The frequencies from 430 to 440 MHz are allocated on a secondary basis to licensed radio amateurs who are allowed to use up to 40 W (16 dBW) between 430 and 432 MHz and 400 W (26 dBW) between 432 and 440 MHz. Channels 1 to 14 are UK Amateur repeater outputs and channels 62 to 69 are UK Amateur repeater inputs. This band is shared on a secondary basis for both licensed and licence exempt users, with the primary user being the Ministry of Defence.

EDIT: The first harmonic of 433Mhz is 866Mhz - this (just) falls outside one of the 4G network (791Mhz - 862Mhz) band allocations - any mobile phone towers near you OP?

Edited by TonyRPH on Wednesday 16th March 09:50