How to identify source of wireless interference?

[turbojimmy]

Okay, this is wacky. People think I'm crazy but I'm convinced that there is a random source of radio interference that jams my car remote and now is jamming my light in my garage.

Here's the deal. After installing an aftermarket remote starter in my car, I noticed that at certain times - and only when the car is parked in my driveway - that the remote ignores my commands. I can't unlock the doors and I can't start the car. I have to use the factory remote (which operates at a different frequency) to get into the car and disable the antitheft system. I've been living with it because it's more or less random.

The plot thickens....

I installed a Liftmaster 3800 garage door opener over the weekend. The light unit plugs into any outlet and receives the on/off commands wirelessly from the motor unit. It worked fine for days but now had stopped working. It stopped working the same day the aftermarket keyless entry stopped working on my car. I suspect they operate at around the same frequency.

I don't know what causes this interference and it comes and goes. It will be good for weeks, then stuff doesn't work for a few days, and then it works again.

I don't know exactly what frequency these things operate at. A quick google search of Code alarm systems makes me think they operate at 433 Mhz. I guess maybe the light in the garage is the same. It's also the same frequency at which my wireless thermometers operate. I pulled the batteries out of all of them but still cannot get my car nor the light in the garage to work.

Anyone have any idea what other household devices operate in the 400 Mhz range? This is driving me nutz.

Don't call me crazy,
Jim

 

[tomcatturbo]

You need a Spectrum Analyzer, with a directional Yagi Antenna. I do this stuff for a living with Cell Phone interference and Towers. It's not an easy thing to do, and requires some common sense along with some technical ability.

What you should do is try and find out what's the common frequency that's causing your grief. Find out what's the interfererer and if it was caused by you.

If your car remote operates on the same frequency range as your garage door opener, then let's just assume that. Unplug 1 or the other and make sure that equipment is operating fine without the other interfering. Once you've determined that, then plug the other in and see how the frequency interfering is causing you problems.

If this is the case, then change out the garage door opener once you've found out if it's on the same frequency range as your car alarm. Try and find out what frequency range it's on and get something that's perhaps shielded or known for being a better system.

It's a matter of isolation and may take a little time. Also, check into your cordless phones frequency as well and anything else with remotes...

 

[turbojimmy]

You need a Spectrum Analyzer, with a directional Yagi Antenna. I do this stuff for a living with Cell Phone interference and Towers. It's not an easy thing to do, and requires some common sense along with some technical ability.

What you should do is try and find out what's the common frequency that's causing your grief. Find out what's the interfererer and if it was caused by you.

If your car remote operates on the same frequency range as your garage door opener, then let's just assume that. Unplug 1 or the other and make sure that equipment is operating fine without the other interfering. Once you've determined that, then plug the other in and see how the frequency interfering is causing you problems.

If this is the case, then change out the garage door opener once you've found out if it's on the same frequency range as your car alarm. Try and find out what frequency range it's on and get something that's perhaps shielded or known for being a better system.

It's a matter of isolation and may take a little time. Also, check into your cordless phones frequency as well and anything else with remotes...

Thanks for the reply.

I've asked both the manufacturer of the opener and the alarm system what frequencies they operate at. The opener remote is 315 Mhz, but I think the wireless communication between the opener and the light fixture is different. I've always had the problem with the aftermarket alarm system. It's random so I've just lived with it. I don't think they're interfering with each other, but whatever was interfering with my car alarm is now affecting the light fixture.

I need to think about what other wireless things in my house use that frequency. My phones are 5.8Ghz so it can't be them. If memory serves, it only happens when it's cold out. I need to mull that piece of information over and see if I can make any sense of it.

Jim

 

[54Rich]

RF issues are hard to find and can come from anything. Without the proper tools, you won't see it so it's a matter of eliminating things as you go.

One of the biggest sources of interference is any electrical motor and if it has brushes it can create a mess. Don't worry about looking for specific things that operate on a certain Fq. Chances are that it's a broadband source. I've seen things like fan motors, buzzers, battery operated pencil sharpeners! One of the most common things are florescent light ballasts. What happens is the noise is across the spectrum and effectively raises the noise floor, your devices are low powered and have to be a certain level above the floor to operate. They get lost in the noise.

When you notice that this is happening, you start to shut things down and hope you can find it that way.

I chased a noise for a year, it would come through on the radio, intermittent just annoying. Then one day, I heard it and just happen to be standing by the refrigerator. The noise related to the cycle of the compressor. Turns out it was a defective thermostat in the fridge.

Another thing is that when you have two transmitt devices setting next to each other, the two Fq. mix and can create mulitpal fq. The effect is Heterodyning. Just an example, it can be almost anything that causes it.

Of course your house might be haunted

Rich

 

[wallyp]

Energy saving light bulbs emit a LOT of RF and infered signals,
using any???

 

[turbojimmy]

Energy saving light bulbs emit a LOT of RF and infered signals,
using any???

No, but here's some more data....

The aftermarket car alarm people confirmed today that the remote operates at 433 Mhz, which is the same as those popular weather stations (I have a few in my house, actually - two are transmitters). I'm pretty sure that the light fixture that is not functioning also operates at 433 Mhz. Again, they're not interfering with each other but the mystery interference is causing both the light and the car remote to not operate.

So I drove around my cul de sac a little. I could not get my remote to respond at all while in the cul de sac. It's only about 200 feet long. Toward the end of the cul de sac I was able to get the remote to lock the car but not unlock it. I left the cul de sac and about 50 feet away from the mouth of the cul de sac I was able to operate the remote for the car normally (lock, unlock, remote start). Back in the cul de sac again it ignored all my commands.

Here's a pic. Green = remote works; Red = remote doesn't work; Yellow = locked but wouldn't do anything else

I don't see a pattern yet, but the source is either my house or someone close to me.

Jim

So the source of the interference is either me or one of my neighbors. I'll have to ask them about wireless devices they may have. Since it's an unlicensed band I have no recourse (can't make them fix it) but I want to solve the puzzle.

Jim

 

[turbojimmy]

Okay - I verified that the light has to be 433 Mhz as well. When I put the light close to the motor it works like it should. The problem is that the receiver antenna on the light has to be almost touching the transmitter wire on the motor in order for it to work which defeats the purpose of having a remote-mounted, wireless light fixture. Regardless, I mounted the light close to the motor as possible the 6' power cord and then ran a piece of bell wire between from its antenna to the transmitter antenna. I know this goofs up the wavelengths of the signal but it's working for now (the bell wire is about 18" long).

I also finished my testing around the 'hood. I've narrowed it down to 2 of my neighbors. When I see them I'm going to ask them. It's a pretty strong signal to completely cancel out both my light signal and the car remote signal. The car remote will work, too, if I put the transmitter right on top of the antenna wire.

Jim

 

[54Rich]

Sounds like you could use some equipment to find it. Try here:

Spectrum Enforcement Division (I wonder if they carry badges )

EB - Spectrum Enforcement Division

Devices are not allowed to transmit unwanted Fq. I wouldn't spend a whole lot more time on it, when with the proper equipment, you could find it in a few minutes. Because it sounds like it's on all the time, should be an easy find.

If I lived close, I'd bring the Spectrun Annalyzer over (and a 12 pack)

Let us know what you find out.

Rich

 

[turbojimmy]

Sounds like you could use some equipment to find it. Try here:

Spectrum Enforcement Division (I wonder if they carry badges )

EB - Spectrum Enforcement Division

Devices are not allowed to transmit unwanted Fq. I wouldn't spend a whole lot more time on it, when with the proper equipment, you could find it in a few minutes. Because it sounds like it's on all the time, should be an easy find.

If I lived close, I'd bring the Spectrun Annalyzer over (and a 12 pack)

Let us know what you find out.

Rich

Thanks - I sent an e-mail to them. I'm not sure I can do anything about it since it's an unlicensed band. But to your point (and I pointed it out in my e-mail) this transmission is constant. The devices that are designed to operate at 433 Mhz typically send short bursts of data at regular intervals (wireless thermometers, for example).

A spectrum analyzer and a 12-pack sounds good. I wish I had one or both right now actually.

I'm glad I got the garage light working. It's not where I want it, but at least I don't have to fumble around in the dark anymore.

Jim

EDIT: The interference is gone now. I just walked to my bedroom window to see if I could lock the car because I forgot to when I got home tonight. Horn honked, lights flashed. It's weird that it was Monday through Friday this week. If history is any indication of the future, the problem won't occur again for another month or two.

 

[Slapshot351]

So turbo jimmy, did you ever solve the problem ?? I'm having the same problems!!

 

[garyk1970]

microwave ovens have been known to cause this??

 

[turbojimmy]

So turbo jimmy, did you ever solve the problem ?? I'm having the same problems!!

Eventually it stopped on its own. Not sure why. I sold the house over a year ago, so I don't know if it ever came back.

Jim

 

[Slapshot351]

Ok, well thanks for the reply. I turned the main off to my house and still have the problem. So I know it's not me. Hopefully it will go away for me too. Thanks again.

 

[garyk1970]

haha...i didnt notice how old this thread was....