The 433Mhz frequency and interference

[Tyler J. Thomas]

Haven't seen much activity on this sub-forum in a while so I figured I'd get a discussion going on an issue I recently had.

We had a wireless activator, the fancy-smancy industry term for a handicap button, on campus stop working. It didn't stop altogether, no it would still work after about 8-9 presses. I started my way from most likely and worked to least likely (or so I presume) to solve the issue. New battery? Nope. New transmitter? Nope. New receiver? Nope. Turns out it wasn't working reliably anymore because of interference. Huh? Really? Okay, I guess.

I usually don't question tech support when they tell me such things. They're the ones that know their product like the back of their hands. But yes, they were absolutely right. I switched to a product on a frequency that was much less utilized and the problem was solved. I had never heard of this particular problem before. I have heard and seen wireless gateways used on wireless access control systems experiencing interference issues but that was only because of physical sources, eg. CMU walls and steel frames.

Apparently 433Mhz, the frequency the original transmitter/receiver operated on, is a very popular radio frequency.

So, anyone else ever dealt with something similar? I know a lot of you work or have backgrounds in IT so I would guess this is a very, again I guess, common problem you encounter. What are your solutions? Repeaters? I have no idea what in the building is now utilizing 433Mhz so much that it causes interference, what else utilizes 433Mhz?

[RumballSolutions]

Many automotive, garage and consumer remotes work on 433Mhz. You may find that proximity to a large car park with numerous smart entry vehicles may be your culprit.

[MatrixBlackRock]

I have no idea what in the building is now utilizing 433Mhz so much that it causes interference, what else utilizes 433Mhz?

433 MHz is in the middle of the 70 cm Amateur Radio band, it is primary allocated to Amateur Radio and is a secondary allocated to radio location both of which are authorized to use a significant amount of transmitter power, up to 1 Kw for Amateur Radio.

Any unlicensed users of 433 MHz are required to not interfere with licensed users and must tolerate any interference created by licensed users, even interference which causes a malfunction or non-operation of the unlicensed device and to add to the mix 433 is also popular with model airplane/drone operators for long range (LRS) FPV control.

As such, my advice would be to avoid 433 MHz altogether and stick with 315 - 318 MHz.

Wayne
WT4FEC

[cledry]

I have had issues with fluorescent light ballasts causing greatly reduced range on remotes as well as issues from battery chargers for electric forklifts.

[cledry]

BTW I looked into fluorescent lights interfering with remotes for locks and in theory the RFI should be in the AM range. We thought possibly it was loose bulbs but that didn't solve the issue. If we shut down the lights near the receiver however the range returned. In the end we moved the receiver.

[MatrixBlackRock]

I have had issues with fluorescent light ballasts causing greatly reduced range on remotes as well as issues from battery chargers for electric forklifts.

That is because they both use switching power supplies, internally switchers are high frequency and being on/off switched are square wave devices and square waves, by their nature, are rich in harmonics, therefore they can interfere with signals well above their switching rate.

Wayne

[Tyler J. Thomas]

I have had issues with fluorescent light ballasts causing greatly reduced range on remotes as well as issues from battery chargers for electric forklifts.

That is because they both use switching power supplies, internally switchers are high frequency and being on/off switched are square wave devices and square waves, by their nature, are rich in harmonics, therefore they can interfere with signals well above their switching rate.

Wayne

Could it have been caused by something not on the same frequency? In other words, if the RF signal was strong enough, regardless of frequency, could it still interfere with my device?

The new transmitter/receiver are on 900Mhz.

[MatrixBlackRock]

Could it have been caused by something not on the same frequency? In other words, if the RF signal was strong enough, regardless of frequency, could it still interfere with my device?

Absolutely, that is known as swamping the receiver, it's like trying to listen to a whisper at a rock concert.

The new transmitter/receiver are on 900Mhz.

918 by any chance?

Wayne

[dontlook]

As Homer Simpson said radio waves, "the cause of and solution to all of mans problems", no wait that was about beer.
Haven't seen this specific issue, but I've heard a lot of stories about 2.5 Ghz and 5Ghz interference. Had some experience tracking devices with tools, its not fun until the end.

Everything folks have said would lend me to agree with avoiding that frequency, there seems to be too many possible talkers and too much variety in protocol. You can sometimes find specialized devices for looking at signal strength and play hot and cold to find the interferers, but they need to be actively transmitting.

There are other devices and open source software that can be used to do similar things. They are often referred to as software defined radio dongles. It may be hard(er) to identify that the creating the signal you are measuring is always the same device.

The HAK.5 guys have done a lot with these dongles in general and explained some of the tools if you want to go deeper in to this.
http://www.hak5.org/tag/rtl-sdr

[Tyler J. Thomas]

Could it have been caused by something not on the same frequency? In other words, if the RF signal was strong enough, regardless of frequency, could it still interfere with my device?

Absolutely, that is known as swamping the receiver, it's like trying to listen to a whisper at a rock concert.

The new transmitter/receiver are on 900Mhz.

918 by any chance?

Wayne

I will check into the actual frequency and get back with you. Love that analogy btw.

As Homer Simpson said radio waves, "the cause of and solution to all of mans problems", no wait that was about beer.
Haven't seen this specific issue, but I've heard a lot of stories about 2.5 Ghz and 5Ghz interference. Had some experience tracking devices with tools, its not fun until the end.

Everything folks have said would lend me to agree with avoiding that frequency, there seems to be too many possible talkers and too much variety in protocol. You can sometimes find specialized devices for looking at signal strength and play hot and cold to find the interferers, but they need to be actively transmitting.

There are other devices and open source software that can be used to do similar things. They are often referred to as software defined radio dongles. It may be hard(er) to identify that the creating the signal you are measuring is always the same device.

The HAK.5 guys have done a lot with these dongles in general and explained some of the tools if you want to go deeper in to this.
http://www.hak5.org/tag/rtl-sdr

Who typically uses these tools? Network admins and engineers? I presume they're costly?

[Squelchtone]

download the sdr# freeware, and buy a $25 dollar USB RTL-SDR dongle here: https://www.amazon.com/RTL-SDR-Blog-RTL ... B011HVUEME . I use mine to listen to digital police transmissions. What you would do it plug it in, install the software, configure your sound card a little and then tune into 433.0000 Mhz and listen to see what's on that freq, plus you could see any adjacent RF causing the inteference, the wave form diagrams and water falls make it easy to spot things that should not be there, and walking around with a laptop and this usb dongle and antenna you can fox hunt around the facility to see where the interference is weakest or strongest and ID the thing causing the issue. it could be a break room microwave, it could be a ballast in a drop ceiling light, or even a wall wart transformer such as the 24VAC kind that power cctv cameras.

example of some radio activity at 99.1000 MHz (a local radio station 99.1 FM) and some noise at 99.4 and another radio station at 99.7000 MHz.


You would tune your software to 433.0000 and see if there was anything bleeding over from near by freqs, and you can do things like turn off lights and motors and turn them on to see if they cause any spikes or noise on or near 433 MHz. you can also trip alarms and motions to see what their transmissions look like, and if their peaks are small, you can zoom in using the software, basically changing the scale of the on screen graph.

Squelchtone

[dontlook]

Squelch is clearly more prepared for this than I am. I would really watch through some Youtube videos on it get an idea for things like the noise floor.
The other issue is you may have multiple devices, moving, transmitting at unknown intervals causing this. However if it is every 8-9 presses maybe it is more consistent and stable than a car remote or other transient device.

The fancier stuff made by Fluke and Co are probably owned only by high end radio technicians whom specialize in this but the SDR community is gaining popularity. The RTL SDR is a good start if it supports the frequencies you need, other devices are HackRF One or for 2.5 & 5 Ghz WiSpy.

As with everything else, practice a bit, do your YouTube watching/reading, run it on some knowns to understand what to expect, and then off to the real world.

[Tyler J. Thomas]

So basically it can be used as a spectrum analyzer?

[Squelchtone]

So basically it can be used as a spectrum analyzer?

well, it's a software defined radio (sdr) where you tune the frequency using the SDR# software which tells the electronics in the RTL-SDR usb dongle what frequency to tune into, so it's more of a radio that listens to a single frequency and a specific mode, but some people have made spectrum analyzer software that works using the usb dongle: http://www.rtl-sdr.com/rtl-sdr-spectrum-analyzer/ but I guess its fair enough to say it's a poor mans spectrum analyzer

as dontlook mentioned, things like the noise floor become important, and calibrating the baselines for everything so you arent looking at random noise thinking it is some sort of nearby signal. even the laptop the dongle is plugged into is going to create noise and birdies which are signals that the usb dongle generates itself in order to work, things like the Clock signal, and oscillators, will show up in multiples across the spectrum, as long as you know they exist you can spot them easily and say, nope, that's a known signal the usb dongle makes, or my laptop's motherboard or wifi card make, and not the cause of my interference.

[jeffmoss26]

Isn't 433MHz a public safety band? My suburb's Police and Fire have not switched to Project 25 and they are still using frequencies around that range.