Hunting down rogue high powered 433Mhz transmitter? - Page 1
Forum section: electronics / projects

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 09:07:15 am
content: G'day All, Im having a really really annoying RF interference issue, just for background at our house we have 2 systems using the 433Mhz frequency range:* remote Garage door opener (Steel-line BOL4)* CurrenCost EnviR Home energy monitoring systemMy Garage door remotes get knocked out for several hours at a time at random times of the day, several times a week. It happens most often in the evenings and completely blocks our use of the Garage door remotes, even standing a metre away from the door results in nothing happening. I even had a brand new control board with new remotes installed at a cost of $200 to try a slightly different part of the 433mhz frequency band (it improved a bit).My CurrentCost Envir also uses the 433Mhz spectrum - this is a home energy monitoring device and my system loses around 15 minutes of data at random times almost every second day of the week. I know it's radio interference as the energy display in the house shows it has lost signal completely despite normally showing full signal strength. I also log the data to my server & PVOutput and get email alerts when it hasn't received data for more than 15 minutes.I've tested the two systems separately while both systems have stopped working - I powered the other off to ensure each wasn't interfering with the other and they weren't. The door still failed to work and the monitoring system failed to receive data.I believe someone nearby is using something that is outputting significantly more than 25 mW of power to knock out two systems like this. Im guessing it's some sort of Wun Hung Low non-aussie RF compliant baby monitor or something that's blasting out it's PoS signal at significantly more than the allowed 25 mW. I've lodged a complaint with ACMA but considering neither of my neighbours has a remote garage door or similar energy monitoring system, I doubt they'll investigate.Soooooo, the real reason for this post- I was wondering if any RF guru's could point me in the right direction to build a Radio Direction finding device. Im probably a bit above beginner level with electronics and can prototype and make simple vera board projects etc, I just lack any useful RF knowledge but happy to learn. Then I can find the pricks stuffing up my garage door etc and tell them to bin the PoS before I report them direct to ACMA for operating an illegal RF device.

author: Dubbie
author_rank: Unknown
timestamp: December 20, 2016, 09:26:40 am
content: You might be surprised. Often they are quite keen to come and poke around with their spectrum analyser.Sent from my phone using Tapatalk

author: nfmax
author_rank: Super Contributor
timestamp: December 20, 2016, 09:29:30 am
content: You are clearly missing the point here - obviously youneedto buy yourself a spectrum analyser! What sort of a nerd do you call yourself?

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 09:29:53 am
content: Quote from: Dubbie on December 20, 2016, 09:26:40 amI put n.a. In their neighbors info page which is why I'm not confident they'll investigate.

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 09:31:32 am
content: Quote from: nfmax on December 20, 2016, 09:29:30 amLol, yeah trust me I want one, I might buy one of those single board jobs from flea bay and use that to get started. I'd love a Rigol but can't justify $400 atm.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 20, 2016, 09:41:18 am
content: I bought myself a RF Explorer to track down WiFi interference. Since it arrived, the interference has stopped. 10/10 would recommend.It's not that expensive. I bought a 3G combo from ebay (15-2700 and 200-900 Mhz-ish or something alike).I've so far used it for a few hours on friday night to see which wifi channels was least used. And I've determined that superheterodyne receivers are evil.

author: Muttley Snickers
author_rank: Unknown
timestamp: December 20, 2016, 09:43:26 am
content: Do you have access to a scanner/ receiver ?.You are welcome to borrow one of mine if you happened to be located in Victoria, I also have a couple of field strengh meters but from memory the upper VHF range is 300 MHz and the lower UHF range is 470 MHz so they excludes the specific frequently you are hunting.

author: jeroen79
author_rank: Frequent Contributor
timestamp: December 20, 2016, 09:56:45 am
content: Apart from a receiver that can indicate signal strength you would need a directional antenna.Then triangulate the source from several positions.

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 10:11:00 am
content: Quote from: Jeroen3 on December 20, 2016, 09:41:18 amNice, I'll have a look and see what I can find. I've never had an issue with Wi-Fi scanning as I use Wi-Fi Explorer on my wife's Mac Book Pro - it's excellent.

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 10:12:52 am
content: Quote from: Muttley Snickers on December 20, 2016, 09:43:26 amI'm out east in Kilsyth - thanks for the offer but I think your scanner skips the frequencies I need.

author: tggzzz
author_rank: Super Contributor
timestamp: December 20, 2016, 10:17:39 am
content: Consider using an $15 RTLSDR dongle plus a laptop and antenna. It should point you in the right direction, ho ho.

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 10:22:43 am
content: Quote from: jeroen79 on December 20, 2016, 09:56:45 amYep I'm familiar with the general concept of radio direction finding (watched too many WW2 docs), just not the the equipment requirements.

author: Psi
author_rank: Super Contributor
timestamp: December 20, 2016, 10:29:36 am
content: any radio controlled planes flown nearby?433mhz is common for the radio link for long range flights. Power is usually up to 0.5WBut yeah, get a cheap USB spectrum analyser and make a directional antenna. Have some fun tracking it down

author: Muttley Snickers
author_rank: Unknown
timestamp: December 20, 2016, 10:30:40 am
content: The scanners I have do receive 433 MHz, the field strength meters I have dont although a little Emitor Digiair does specify 47 - 862 MHz but I've just had to put in on charge to check, pretty sure that one skips also.Put the kettle on, I'm working in Kilsyth either Thursday or the day after boxing day, just waiting on a meter to turn up then I should be good to go.

author: Psi
author_rank: Super Contributor
timestamp: December 20, 2016, 10:35:26 am
content: with a SDR usb receiver you could have a look what the traffic is.If its simple analog audio from a baby monitor you can listen in

author: Muttley Snickers
author_rank: Unknown
timestamp: December 20, 2016, 11:00:25 am
content: wilfred is right, a soft approach first up is always the best method and if that doesn't work then go hammer and tongs, also some wireless security alarm systems do use 433 MHz as well so that is another source to consider.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 20, 2016, 11:02:39 am
content: Quote from: djos on December 20, 2016, 10:11:00 amYou'll only see legitimate 802.11. And not bluetooth or other 2.4 GHz users. Such as wireless headphones or speakers. This mistake is often made though.

author: Psi
author_rank: Super Contributor
timestamp: December 20, 2016, 11:37:08 am
content: Do you have a smart power meter on your house?I think some types use a mesh network, probably 433mhz.It could be the time of the day when they all do their data dump. It would explain why your 433 mhz devices are so completely jammed if every smart meter in the street is taking on a mesh network for 15min a day.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 20, 2016, 12:10:04 pm
content: Definitely set up a cheap RTL-SDR system - even without direction finding this should tell you a lot about the source - type of modulation, exact frequency etc. Also logging times it's active may give you some significant cluesAt 433 you could maybe use a TV yagi antenna for direction findingWhoever regulates radio spectrum in your country may have some duty to investigate this sort of thing. Although 433 is unlicensed there are restrictions on things like duty cycle etc.

author: spudboy488
author_rank: Regular Contributor
timestamp: December 20, 2016, 12:24:31 pm
content: Contact a local amateur radio club and see if they want to try a fox hunt to help find the source. They will have directional antennas that would really help locate the source. Spectrum analyzers alone are OK but without a directional antenna, you would be a bit aimless as you walk around looking for peaks.

author: Bud
author_rank: Super Contributor
timestamp: December 20, 2016, 02:17:13 pm
content: If it is possible to hack into the receiver or between the receiver and antenna, try a bandpass filter.

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2016, 02:24:43 pm
content: Why don't you pick up a $15 RTLSDR on ebay and try that first? It will likely show you the problem or make it easier to find. An RTLSDR makes a fine 433 MHz receiver. You could also use it to listen to FM radio, and hundreds of other things.No need to spend a lot of money on one with all the extras. Go to YouTube and plug in "rtl2832 + R820t" There are instructions athttp://osmocom.org/projects/sdr/wiki/Rtl-sdr

author: LaserSteve
author_rank: Super Contributor
timestamp: December 20, 2016, 03:15:09 pm
content: You might need to know who your RF neighbors are...http://www.wia.org.au/members/bandplans/data/documents/Australian%20Band%20Plan%2070cm%20150729.pdfYour in a shared band, with two services having a higher priority then you,One is mil RADAR...Steve

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 09:04:57 pm
content: Quote from: tggzzz on December 20, 2016, 10:17:39 amThanks much appreciated.

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 09:08:06 pm
content: Quote from: Muttley Snickers on December 20, 2016, 10:30:40 amI'm off to Adelaide tomorrow for 2 weeks, can I give you a pm when I'm back?

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 09:13:33 pm
content: Quote from: wilfred on December 20, 2016, 10:45:43 amYeah, I'm just grumpy after putting up with this for over 6 months and spending $200 on a new garage door control board and another $110 on a Wemo maker as a backup solution to when the door isn't working. So my wife and I can get in and out of the garage.

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 09:15:29 pm
content: Quote from: Psi on December 20, 2016, 11:37:08 amYes we do, I think the Victorian ones either use 3G or WiMax tho?

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 09:16:40 pm
content: Quote from: cdev on December 20, 2016, 02:24:43 pmCheers, I'll definitely do this.

author: Muttley Snickers
author_rank: Unknown
timestamp: December 20, 2016, 09:33:10 pm
content: No problem here and I hope you can locate the issue, I was serious about having to head over to a plant in Canterbury Road over the next few days though and good start with these intermittent occurrences is to start a log file or list by recording the time, date and duration if possible if you intend to ferret it out yourself, these can be intriguing at times so you might need to put your Miss Marple hat on and Communications Systems Interference or CSI Kilsyth as we like to call it could be quite a story to tell in the future.

author: djos
author_rank: Unknown
timestamp: December 20, 2016, 09:40:01 pm
content: Quote from: Muttley Snickers on December 20, 2016, 09:33:10 pmCheers, I enjoy problem solving but needed some help on the hardware side, thanks to all for the help, it's much appreciated.

author: David_AVD
author_rank: Super Contributor
timestamp: December 20, 2016, 09:53:23 pm
content: Is there a particular model of RTLSDR that's better, but still on the cheaper side? There are quite a few on eBay to choose from.I was thinking of getting one, but not fond of the old "PAL" antenna connector. SMA would suit the 433MHz leads and antennas I already have.

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2016, 09:59:35 pm
content: The rtl_power command line program that comes with the drivers from osmocom can be scripted to scan any arbitrary frequency band and write its output to a csv file which you can then visualize in the time dimension. This can be very useful for clues as to when the transmissions are occurring (because you could never monitor the whole frequency spectrum by hand, yourself.)Also, if you look around, the US government (and I am sure some others do too) has a number of publications written for scientists and the military on finding the sources of RFI. Also, Youtube user SM5BSZ has several videos on the self-construction and use of small electrical and magnetic field probes to locate EMI. He's very knowledgeable and these videos contain a wealth of information. He is the author of a SDR program which can be used with the dongles. Another, newer program which many people use is CubicSDR.

author: daveshah
author_rank: Unknown
timestamp: December 20, 2016, 10:03:22 pm
content: Quote from: David_AVD on December 20, 2016, 09:53:23 pmI don't think there are massive performance differences between any of the cheap ones with a R820T. None that I know of have SMA connectors but there are some cheap MCX (which is common on them) to SMA adapters on eBay.

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2016, 10:10:02 pm
content: I have no personal experience with it but there is a blog the "RTLSDR blog" that sells a significantly upgraded dongle for around $25 (from memory so may be wrong) which has an SMA and a 1ppm TCXO as well as a metal case. Also, I think it may have a jumper or some way to provide low voltage DC on the antenna wire which is very useful if you want to use an antenna-mounted LNA. (a built in ghetto style bias-tee)Thats probably the one to get if you want to spend a bit more.

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2016, 10:19:53 pm
content: Its a real PITA to replace a Beiling Lee/PAL connector with an SMA with just a soldering iron but easy with a hot air gun/pencil if you have one.

author: vk6zgo
author_rank: Super Contributor
timestamp: December 20, 2016, 11:42:11 pm
content: Quote from: LaserSteve on December 20, 2016, 03:15:09 pmAs Steve points out,you are in asharedband.To make matters worse,you are "at the bottom of the food chain",& can havenoexpectation of immunity from interference.Amateur Radio Operators,although the "Secondary Service" on this band,are quite within their rights to use 400w PEP,& various modes.The Primary Services of Radiolocation,& Point to Point Services,although rarely seen,may use considerably more power.Low Interference Potential Devices (LIPDS),such as your gadgets are allowed on 433MHz because they supposedly are unlikely to cause interference to the Primary & Secondary Services.(Google for LIPDs)Unfortunately,due to their proliferation,they do cause interference,both to other services & between themselves.The receivers used in LIPDs aren't very good,either,so they may receive strong signals from adjacent bands.(military,etc,just below 430MHz)We had a proper allocation for remotes,etc at 315MHz,but the few remaining EEs in ACMA got "rolled" by the "suits",so importers could bring in cheap 433MHz crap.

author: djos
author_rank: Unknown
timestamp: December 21, 2016, 01:02:13 am
content: Quote from: wilfred on December 20, 2016, 10:32:38 pmI doubt it, I'd notice that!Nothing using 433 Mhz, no.

author: Jay1011
author_rank: Contributor
timestamp: December 21, 2016, 02:27:17 am
content: Also consider LED bulbs, those in your own house as well as perhaps ones your neighbors may have installed in nearby locations.The cheap LED bulbs -- as well as some not-so-cheap ones -- are well-known for spewing all over the spectrum and interfering with garage door remotes and the like. I had that experience myself, actually. LED bulb from a company called HyperIkon (US brand name) rendered my garage door opener completely nonfunctional when the bulb was on. When the bulb was off, all worked fine. I switched to a Philips brand bulb and no more problems bulb on or off.

author: djos
author_rank: Unknown
timestamp: December 21, 2016, 02:30:19 am
content: Quote from: Jay1011 on December 21, 2016, 02:27:17 amI've come home to a powered down house many times to find my Garage door wont respond so Im fairly confident my LED's aren't the cause. Like you Im running Philips LED's in the entire house without issues.

author: Muttley Snickers
author_rank: Unknown
timestamp: December 21, 2016, 02:50:26 am
content: For the garage door reliability you can always connect a completely different remote control and receiver card operating on another frequency altogether should the current issue not be identified, you simply wire the momentary dry contacts from the new receiver to the terminal input on the door motor controller where a fixed button would normally be wired in. Ideally this should be powered from a separate backed up supply but your door wont open anyway if the power is out so it's optional really. This won't help with the energy monitoring system though as you well know but at least it's a start.

author: djos
author_rank: Unknown
timestamp: December 21, 2016, 04:23:35 am
content: Quote from: Muttley Snickers on December 21, 2016, 02:50:26 amWe've had a new board operating on a slightly different frequency Installed that required new remotes. It improved but we still get periods where you can stand under the unit and press the remote and it might as well be powered off ... nothing happens.As mentioned in an earlier post, I grabbed aWemo Makerfrom Bunnings and wired it up to the "wired door button" terminals in momentary mode. Plus I added a normally open magnetic security sensor so we can use our phones to see if the door is closed/open and open/close it if the remotes are blocked. To make it even easier for the Wife, I created an IFTTT recipe and added the Do widget her her lock screen (and mine) so she can easily and quickly operate the door if the remotes are blocked.The energy monitoring system is not affected nearly as much or as badly as it operates on a slightly different frequency to the Garage - Im not bothered if I lose 10mins here or there every few days, it's a minor nuisance compared to the garage door not allowing ingress or egress.

author: djos
author_rank: Unknown
timestamp: December 21, 2016, 08:48:03 am
content: Quote from: wilfred on December 21, 2016, 06:24:56 amI've been having a private chat to Muttley (thanks mate) and he's suggested there could be an intermittent fault with the new control board based on the fact that when it stops working it's as if it is dead, even standing under it with the remote when it's playing up doesnt produce a result. Both previous boards still worked when standing under them, just not from2 metres away.As a result I'll get Steel-line back out to replace the board in the new year. TBH they've been pretty darn good to deal with so far and their tech is a top bloke to chat to.Quote from: wilfred on December 21, 2016, 06:24:56 amYes I log all the failures to capture data over 15 minutes in duration to email which I can then cross reference with the missing data in PVOutput. see attached:

author: djos
author_rank: Unknown
timestamp: December 21, 2016, 10:19:04 am
content: Quote from: wilfred on December 21, 2016, 09:42:07 amDecember 20th is the top most item. You're quite correct, there are more missing data points but I'm only logging the 15 minute plus losses or my mailbox would be smashed even harder than it already is. Kudos for looking up my data on PVO.The transmitter uses 2 D cells which last four about 4 years, these ones are about 9 months old. It uses a standard CT clamp on the mains active wire going into the switch board. Simple but accurate enough for my needs.The receiver is on a UPS along with my server. Even if the receiver loses connection to the server (good old fashioned reliable RS232), it stores several days worth of data which the service on the server will extract next time it connects.I've done the isolation tests, they aren't inferring with each other.Regarding the garage door, it's a single board solution but the power supply is separate, I thought that wasn't the case but I just popped the back off to confirm.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 21, 2016, 11:41:43 am
content: You should have seen capture effect, or near field saturation when standing right under the door receiver. Unless you have a Tetra site or a radar right on top of you, or the very unlikely ATV transmitter, my bet is your interference source is within feet of you.Any big towers within a kilometer or two?Steve

author: Buriedcode
author_rank: Super Contributor
timestamp: December 21, 2016, 04:42:57 pm
content: After designing a 433MHz 'basic' network for home automation, I looked at the spectrum and there were indeed *many* transmissions flying about on this band. However, things like wireless doorbells, car alarms, weather stations etc.. are all rather low duty - from 2-3 bursts a day, to every coupe of minutes, certainly not something that would kill a link for hours at a time unless your kit juts so happened to transmit at exactly the same time as the interference (so unlikely, not really worth bothering with).So it looks like its either:- a continuous interference - not necessarily an active 433Mhz transmission, could also be EMI generated from something else,- the antennas of your systems are poorly placed.. or.. just-so-happen to be in dead spots.- your equipment is faulty.After reading the thread is seems like that the 3rd option is unlikely. And I'm sure you would have eliminated the second by moving things about (especially in the case of a garage door opener, side step and chances are if it was multipath, it would work fine).So whilst I've just come back to what you suggested in your first post, best to eliminate other things first!As suggested, the only real way is to 'see' the band with an SDR. This will also be able to show if its a bonafide 433Mhz transmission, or random noise something is kicking out across this band.It would have to be a particularly powerful signal to interfere for long periods of time, most likely that is because the source is close to you.

author: macboy
author_rank: Super Contributor
timestamp: December 21, 2016, 06:59:37 pm
content: Quote from: Jay1011 on December 21, 2016, 02:27:17 amI had an issue with LED bulbs and my opener. The bulbs cause no issues in the ceiling fixtures of the garage (5 feet away from the opener), but if I install one in the opener itself, then it will not work at all when that light is on. Not even from 1 foot away.

author: djos
author_rank: Unknown
timestamp: December 22, 2016, 09:04:55 am
content: Quote from: macboy on December 21, 2016, 06:59:37 pmInteresting find, I have a Philips LED globe in mine, I might switch it for an incandescent globe just to see if it makes any difference. (In 2 weeks when I get home from holidays)

author: djos
author_rank: Unknown
timestamp: December 22, 2016, 09:08:31 am
content: Quote from: LaserSteve on December 21, 2016, 11:41:43 amAbout 10 kms away we have a stack of transmitters for FM radio, TV etc on top of the Yarra ranges near us but no military bases anywhere near us that I'm aware of.From your comments, and others, I'm beginning to think the new board has an intermittent fault.

author: djos
author_rank: Unknown
timestamp: December 22, 2016, 09:56:57 am
content: Got a "dear Joe public" email from ACMA today advising me to try everything I'd already tried - clearly it was a form letter.No big deal, I have a few avenues to try when I get home from holidays in 2 weeks.

author: cdev
author_rank: Super Contributor
timestamp: December 22, 2016, 05:06:05 pm
content: I would be happy that the failure mode was simply not being able to open the door without getting out of one's car, and not have the garage door open!Can (OP) turn off the RF receiver part of your garage door opener and use a key switch mounted next to the door as a back up?It seems that so many devices use the 433 MHz band now that many now have collisions.

author: djos
author_rank: Unknown
timestamp: December 22, 2016, 08:34:56 pm
content: Quote from: wilfred on December 22, 2016, 10:27:36 amThe other 2 boards always worked if you were standing under the door opener, just frequently not from 2 meters away. When this one doesn't work, it the remote does nothing even when centimetres from the antenna.

author: djos
author_rank: Unknown
timestamp: December 22, 2016, 08:37:55 pm
content: Quote from: cdev on December 22, 2016, 05:06:05 pmAs mentioned previously, I've installed a Wemo Maker connected to the wired door button terminals (relay in momentary mode) so we can fail back to our phones if the remote stops working.

author: TheDane
author_rank: Regular Contributor
timestamp: December 23, 2016, 11:37:31 am
content: If the transmitter does not activate the door when it isright next tothe receiver (or left, above or below) it sounds like it's not an interference issue. (Otherwise the interfering part has to be REALLY REALLY REALLY high power).There's something called near field, and far field - and being too close to the receiver can over load the input, causing distortion and no response/valid signal. Beware of that too!If possible, try to wrap the receiver in alu foil - and leave a big enough gap for you to handle the transmitter. If it is interference causing it not to work - making a faraday's cage should make it work.(Cover your hand in alu foil too - a few gaps and holes are ok, 433MHz has a wavelength of 70cm - hence it's called the 70cm band in ham terms)Wiring to your AC line, and motors can act as antennas - and if the product hasn't passed EMC standards it could be the problem. Ferrite cores and chokes are great for shielding against this kind of noise.I would think the receiver/control box has an issue. If you have access to the schematic and/or test tools - try locate the 'RF remote has sent open/close' 'microcontroller' pin, and monitor that as you activate the remote.Good luck

author: TheoB
author_rank: Regular Contributor
timestamp: December 24, 2016, 08:44:49 pm
content: The receiver input stage is often not selective. The same is true for the antenna. The interferer could very well be not in the 433MHz band so make sure you search wide enough. One receiver can perform better with blockers than another. You have now two receivers that both become deaf every now and then. If the blocker is outside the band a selective bandpass filter could work. This costs money so it is not standard. Good luck with the hunt.

author: TheSteve
author_rank: Unknown
timestamp: December 24, 2016, 11:40:57 pm
content: You can use an SDR to "see" the signal but it won't help you track it down much unless you recognize what it is, same with a spectrum analyzer. Assuming you can pickup some sort of signal the bestway to track it down would be with a traditional style dual conversion etc receiver, a directional antenna tuned for the frequency of interest(easy to build) and an offset attenuator. This is pretty much the standard kit for an amateur radio fox hunt(hidden transmitter hunt).The key to getting really close to the transmitter is the use of the offset attenuator(really just a mixer). Without it the receiver will just overload and you will not be able to get a sense of direction with the antenna. An SDR with a wide front end still generally overloads even with the offset attenuator which is why a more traditional style receiver is preferred.This is the offset attenuator I use:http://www.homingin.com/joek0ov/offatten.htmlThis is my favorite style of DIY yagi directional antenna:http://theleggios.net/wb2hol/projects/rdf/tape_bm.htmYou'd need to adjust the element length and spacing of course for 433 MHz.

author: BrianHG
author_rank: Super Contributor
timestamp: December 25, 2016, 12:51:45 am
content: I recently look at making a 433Mhz tracker for lost parachute canvases. When I purchased some sample radios and transmitters from china, I did some tests with 1w and 3w transmitters with headphones on the radio. There was soooooo much traffic on the radio in my neighborhood, even my 3w transmitter was useless after within a city block. I took the radio in my car and found at least 3 regular packet transmitions which cycled non-stop over a good part of the city. I believe one of them might be used for synchronizing traffic lights from block to block. There is no way such a repeating signal with so much power ran the length of 3 major roads, a few Km long each, through the city, yet, these particular packets faded away quick when entering a residential housing section.433Mhz is used all over the place. Power transmition above 25mw are allowed for commercial applications such as tracking ID transmitters on shipping container, they go up to 3W. But, these transmitions are supposed to be short on and off, with a long silence period in-between packets. Now, if you have 20 to 100 of these containers bursting packets one after the other, this would make a continuous stream of interference.As for radio selectivity, yes, nearby transmittions at even +/- 25 Mhz can still saturate most cheap 433Mhz receivers which aren't superherts with good antena filtering.!!!!!!!!>>> We are also ignoring something else important here: When the garage door opener MCU receives some junk from alternate sources, even if that junk is short, it may be poorly programmed an the software may be crashing, or, ignoring the input for an excessive amount of time. It just may be some new recent 433mhz quick and what should be a harmless transmition has begun to lock up the MCU in the garage door, not that this new interference is over powered, or, continuously on for hours a day. This is why even when you are right at the receiver, it will NEVER work.> TEST: when your garage door wont respond, cut it's AC power for 10 seconds, then reconnect. Test your remote within a few seconds. If you can get your garage door to respond this way, it is likely that the MCU is locking up due to a stray transmition which happens to be just right to crash it.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 25, 2016, 04:44:01 am
content: I also forgot, not all the units are SAW stabilized, our transmitter has a hole in the side for a non-conductive tuning tool, and needs a peaking every two years or so. A low tx battery results in the rolling code losing sync, too.Steve

author: LaserSteve
author_rank: Super Contributor
timestamp: December 25, 2016, 04:47:38 am
content: Oh, Set the internal code dip switch if it has one, to a new oddball binary number on both The tx and the remote.Steve

author: mos6502
author_rank: Frequent Contributor
timestamp: December 25, 2016, 03:51:20 pm
content: Bit late, but pertinent to the topic: 433 MHz direction finding using a cheap receiver module and some random hardware parts:http://www.instructables.com/id/433-MHz-tape-measure-antenna-suits-UHF-transmitte/

author: djos
author_rank: Unknown
timestamp: December 25, 2016, 09:33:48 pm
content: Quote from: mos6502 on December 25, 2016, 03:51:20 pmNice find, the Yagi design in particular will be handy.

author: djos
author_rank: Unknown
timestamp: January 27, 2017, 04:21:21 am
content: G'day all, time for an update:I got Steel-line out last Tuesday to replace the RF board in the Garage door (same model and freq etc as #3), the tech wasnt thrilled (fair enuf, now onto it's 4th board) and voila, the door has been 100% reliable for the past few days! So im convinced those of you who thought the last board had an intermittent fault, where indeed correct.The door remote's have never worked so well, ever! Even the internal house remote (wall mount style) now works!I still bought an R820T2 tuner and a matching 6dbi 433Mhz antenna to have a look at what is knocking out my Energy monitoring system - the antenna isnt directional, but making a small Yagi antenna will be my next project.

author: cdev
author_rank: Super Contributor
timestamp: January 27, 2017, 04:57:53 am
content: You likely could make a very small Magnetic Loop for 433 MHz using the RTLSDR waterfall display for tuning. Use a high quality capacitor, a butterfly cap would be best if you can find one. A magnetic loop has a sharp null broadside to the plane of the loop. Look for "70 cm loop" if any such plans exist. A Yagi would be good too. Both would be easy to build because of the small size.A "Planar Disk" antenna makes a good general purpose broadband antenna.http://www.wa5vjb.com/references/PlanarDiskAntennas.pdf

author: james_s
author_rank: Super Contributor
timestamp: January 27, 2017, 05:09:03 am
content: 433MHz is sometimes used for long range FPV RC flying for the RC control. It's possible someone is flying a plane or multirotor in the area.

author: djos
author_rank: Unknown
timestamp: January 27, 2017, 05:40:34 am
content: Quote from: james_s on January 27, 2017, 05:09:03 amUnlikely, In australia 433.05 to 434.79 MHz is restricted to 25mW low power devices like door openers & weather stations etc.You can read more about the Aussie uses here:http://acma.gov.au/theACMA/spectrum-at-434-mhz-for-low-powered-devices

author: cdev
author_rank: Super Contributor
timestamp: January 27, 2017, 05:58:11 am
content: Where I live I canreceive several weather stations at 433.9 MHz, so who needs to buy one if you haveneighbors who already have them!

author: djos
author_rank: Unknown
timestamp: January 27, 2017, 06:24:07 am
content: Quote from: cdev on January 27, 2017, 05:58:11 amWe have a few nearby that are on Wunderground, even easier.

author: james_s
author_rank: Super Contributor
timestamp: January 27, 2017, 04:56:41 pm
content: Quote from: djos on January 27, 2017, 05:40:34 amWhat is legal and what people are doing are sometimes two different things. You can buy the higher powered transmitters direct from China.

author: djos
author_rank: Unknown
timestamp: January 27, 2017, 09:30:55 pm
content: Quote from: james_s on January 27, 2017, 04:56:41 pmTrue, but if you use high powered transmitters illegally there's a high chance you'd be caught and fined.

author: james_s
author_rank: Super Contributor
timestamp: January 27, 2017, 10:59:14 pm
content: That's how it's supposed to work, but at least in the US there doesn't seem to be much enforcement. I got a technician class ham license for my FPV flying activities but very few people bother.

author: jancumps
author_rank: Unknown
timestamp: January 27, 2017, 11:22:09 pm
content: if someone in your street has a newborn, ask them to put their babyphone on channel B. All your problems solved

author: djos
author_rank: Unknown
timestamp: January 27, 2017, 11:27:15 pm
content: Quote from: james_s on January 27, 2017, 10:59:14 pmI can imagine it's a lot harder to police in the U.S. considering your population size and sheer number of populated cities. Our land mass may be similar in size to the U.S. But we barely use any of it, we are mostly concentrated in 7 relatively small (population wise) cities.Acma (our regulator) seems to frequently bust ppl using spectrum illegally (based on press releases).

author: james_s
author_rank: Super Contributor
timestamp: January 27, 2017, 11:40:04 pm
content: Those RTL dongles are amazing, that reminds me, I really must dig mine out and have a look at what recent developments there are. I did quite a bit of playing around with those a few years ago, it was one of those revolutionary events where the cost of entry into SDR dropped orders of magnitude overnight.

author: djos
author_rank: Unknown
timestamp: January 28, 2017, 01:03:37 am
content: Quote from: jancumps on January 27, 2017, 11:22:09 pmI'm pretty sure I know who it is, but I'm waiting for my SDR dongle and antenna to arrive before I bail up an otherwise excellent neighbor.At least the garage door issue is solved, it's completely flawless now.

author: djos
author_rank: Unknown
timestamp: January 28, 2017, 01:15:38 am
content: Quote from: james_s on January 27, 2017, 11:40:04 pmI've been looking at rtl_433 and the other tools, looks like fun! I wonder if it'll read my Oregon Scientific weather station. Should be fun.

author: djos
author_rank: Unknown
timestamp: February 06, 2017, 07:20:24 am
content: So this arrived today, should be interesting to see what's broadcasting in our area.Building a yagi antenna will be the next project.

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: February 06, 2017, 05:31:33 pm
content: This should suit your needs easily:http://www.instructables.com/id/433-MHz-tape-measure-antenna-suits-UHF-transmitte/step4/Alternative-DIY-UHF-Yagi/

author: james_s
author_rank: Super Contributor
timestamp: February 06, 2017, 06:51:44 pm
content: The Oregon Scientific protocol has been reverse engineered and documented, I was able to receive and decode it with mine. Last I checked though the development of rtl_433 seemed to have stalled.The RTL dongle works great as a police/emergency services scanner, it will also pick up the business band, FRS radios, baby monitors, fast food drive through intercoms and internal coms, pager signals, those aren't nearly as common anymore but doctors still use them. All sorts of interesting stuff flying around in the air.