RF communication system, very little data but >1km range - Page 1
Forum section: electronics / projects

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 03, 2015, 11:01:00 am
content: So for a little project I have planned for this summer, I need a way to get a signal wirelessly to a central controller.The project it for airsoft and milsim scenarios, where there will be 3 or 4 points out in the field that need to be controlled and set to one of the two teams.The range is a few hundred meters, but I would like at least 1km to be on the safe side.The "field stations" will have a switch that can be set to on of 3 positions (neutral, team A, team B). the point is that all 3 (or 4) stations have to be set to the correct team for the team to win the game (say because it's supposed to represent the controller of a bomb or whatever). I would thus need a way to communicate this setting from the stations to the main core(s).I was thinking of using some pre-made RF modules to do this, but the ones I can find either don't have the range I need, or cost to much (I would like to stay under 25 euros per ground station).My RF skills are way to poor to actually design one myself. Anyone have any suggestions?I was thinking of going for a simple microcontroller that would send out a digital pulse at random intervals containing the setting of the switch (average of a second or so between pulses). By making my data pulses short enough, and simply having the core ignore garbage, I think this would be a robust enough way to signal.One last note: I would like to stay out of the 430-ish MHz bands, since this is where most wireless comms work that teams use in-game, and I wouldn't like to interfere/be interfered by them.

author: deephaven
author_rank: Frequent Contributor
timestamp: June 03, 2015, 11:07:18 am
content: Easy Radio are now quoting up to 1.6 mile range for their modules:http://www.lprs.co.uk/easy-radio/modules/

author: eneuro
author_rank: Super Contributor
timestamp: June 03, 2015, 11:22:43 am
content: For remote controled lawn tractor I consider using cheapy lower range modules, but implement on a yard as a few low cost reapeaters with dipole antenas within perfect operating range , but had no time to test it yet if they will get benefit of connecting dipole antena (half wavelength) vs quater length antenas sugested in those 433Mhz cheapy modules manuals

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 03, 2015, 11:28:48 am
content: Thanks for the fast reply. I will check them out.However, the 900mhz one seems to be only 1mw, so I'm guessing their 1.6mile range is only for the 10mW 430Mhz version?I should be able to do some ballpark calculations on this soon (I have exams in both digital and analog communication systems and EM waves this month) - but I do not yet have the time.And I really need quite some range, and I need it to be reliable - If my device doesn't work, I will be letting 200 players down.

author: dom0
author_rank: Super Contributor
timestamp: June 03, 2015, 11:31:36 am
content: Quote from: TheUnnamedNewbie on June 03, 2015, 11:28:48 amBetter build a current loop interface in and bring some cable as a backup(*). If you're in europe you can get Feldtelefonkabel (your army probably has another name for it) cheaply ; they're sold in Germany for about 40 € per 800 m roll.(*) There is a saying "Wer Funk kennt, nimmt Kabel" - "Who knows wireless, uses cables".

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 03, 2015, 11:44:18 am
content: I guess cable is an option, I just thought it would be cool to be able to do it wirelessly - and I have worked with RF modules before, but the range we needed was a lot shorter, but I thought they were more capable than those we used (which turns out only have 80m of range).

author: Dragon88
author_rank: Regular Contributor
timestamp: June 03, 2015, 11:49:34 am
content: There are some cheap wireless modules in the 315 MHz range, but you'd have to check if that band is legal in your country.To be honest, there are so many wireless modules available these days, I'm sure you'll find something. Just depends on the frequency, power output, and cost you are going for. There are however some things you can do at the ground stations to increase link quality, regardless of the module you choose. You can set up a good antenna at each station, likely a monopole or dipole. You could go with directional as well if you want to spend a little more time building them. The antenna at the control station will depend on the arrangement of the outstations. If they are arranged 360 degrees around it, you'll have to stick with an omni. If they are all arranged to one side, you would go for something with a wide main lobe, like a moxon. A moxon is fairly easy to build, and I have always been happy with the results from them.Basically what I'm saying is, don't ignore the antennas. You may find you can get away with a cheaper wireless module all thanks to some scrap wire and a couple hours of construction.

author: daqq
author_rank: Super Contributor
timestamp: June 03, 2015, 11:51:51 am
content: There's a fair amount of RF modules that can do such a thing:http://www.csgshop.com/product.php?id_product=86http://www.telit.com/products/product-service-selector/product-service-selector/show/product/lt70-868/I've used other Telit modules, they were pretty good.QuoteThey are reliable most of the time, but for 100% reliability a cable is the best option - weather and other ambient conditions (even malice) can greatly affect the range of stuff like this.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 03, 2015, 12:23:32 pm
content: Quote from: daqq on June 03, 2015, 11:51:51 amThanks for the reply, but I think these are out of my budget. For what I need them to do, that would prolly end up costing 100 bucks per station, and that is too much.Quote from: Dragon88 on June 03, 2015, 11:49:34 amWell, I would like to stick to omni for flexibility reasons.But yeah, I know I shouldn't ignore my antennaes, but I know too little about EM waves to do propper antena design myself.

author: tggzzz
author_rank: Super Contributor
timestamp: June 03, 2015, 02:33:54 pm
content: In most countries there are laws against people creating their own transmitters and operating them. There are carefully specified licenced exemptions.Your best bet of avoiding prosecution is to start with existing legal transmitters.Radio hams are a good source of information on such topics.

author: niekvs
author_rank: Contributor
timestamp: June 03, 2015, 02:57:52 pm
content: These seem to offer a few km and use the TI C1101, which should be fairly simple to use:http://www.aliexpress.com/item/RFC-1100H-Long-Distance-2w-CC1101-Wireless-Module-w-Antenna-2km-3km-433MHz-GKSK/32288070147.htmlhttp://www.ti.com/product/cc1101Haven't tried them though. But there are many cheaper CC1101 modules on aliexpress (e.g. 4 euro), so that would suggest this particular one (which isn't very cheap) would have a better range. It has a listed transmit power of 2W.

author: bookaboo
author_rank: Frequent Contributor
timestamp: June 03, 2015, 03:16:29 pm
content: Quote from: deephaven on June 03, 2015, 11:07:18 amThe ERIC range from LPRS has very good range for a low end module you *might* get 1K out of that environment depending. The ER modules linked are older and I'd doubt they would go further than 250m even in good conditions.

author: dom0
author_rank: Super Contributor
timestamp: June 03, 2015, 03:47:08 pm
content: Quote from: TheUnnamedNewbie on June 03, 2015, 11:44:18 amBut field phone cable is much more authentic! :-)

author: georges80
author_rank: Frequent Contributor
timestamp: June 03, 2015, 04:00:54 pm
content: www.digi.comhave a variety of modules. A few I use are in the USD$40 range. They have models/versions that are compliant with the ISM bands of various countries.Mouser & Digikey amongst others are distributors.cheers,george.

author: free_electron
author_rank: Super Contributor
timestamp: June 03, 2015, 04:02:19 pm
content: loRa

author: IanJ
author_rank: Unknown
timestamp: June 03, 2015, 04:05:08 pm
content: Speak to Thomas here:-http://www.tslrs.com/Ian.

author: Fungus
author_rank: Super Contributor
timestamp: June 03, 2015, 04:09:57 pm
content: I haven't personally tried them at 1km but that's what these claim to do:http://www.ebay.com/sch/i.html?_nkw=nrf24l01+antennaPower consumption is very low (15mA) so they can easily run on batteries.You can easily create little relay stations using them if the range isn't enough there's line-of-sight issues.

author: hagster
author_rank: Frequent Contributor
timestamp: June 03, 2015, 04:30:47 pm
content: I'd recomendhttp://www.synapse-wireless.com/iot-products/core-iot/rf-modules/They are fully self meshing and are programmed via a lite version of python. It wouldn't take much code at all to do this. You can also add nodes to increase the range of the mesh. Range is about 1 mile LoS.

author: TerminalJack505
author_rank: Super Contributor
timestamp: June 04, 2015, 01:54:39 am
content: Quote from: free_electron on June 03, 2015, 04:02:19 pmYes, this sounds like the perfect application for the new LoRa technology: long range, low data rate.If you can get some LoRa modules then that might be the way to go. It's still pretty new technology, however, so you might have a hard time getting your hands on modules that aren't still in the "engineering samples" stage.

author: deephaven
author_rank: Frequent Contributor
timestamp: June 04, 2015, 08:20:55 am
content: Quote from: bookaboo on June 03, 2015, 03:16:29 pmThe latest ER modules can be set to a narrow bandwidth allowing greater range than the comparatively wide bandwidth of the ERIC modules. LPRS themselves are stating a range of up to 2.5km for their ER modules.

author: tautech
author_rank: Super Contributor
timestamp: June 04, 2015, 08:56:10 am
content: I've tested these guys products to 10 Km LOS and use one of their little pendant remotes to 500m almost daily.Count on their 1Km units delivering your needs.I got 4 Km LOS when I tested them. (naked PCB's on 12V)They did 315 & 433 MHz IIRChttp://www.rfremotech.com/Others.htmlhttp://stores.ebay.com/RFRemotech?_rdc=1

author: bookaboo
author_rank: Frequent Contributor
timestamp: June 04, 2015, 09:43:52 am
content: Quote from: deephaven on June 04, 2015, 08:20:55 amI stand corrected, I didn't know about their new ER version.

author: georges80
author_rank: Frequent Contributor
timestamp: June 04, 2015, 03:05:26 pm
content: Quote from: tautech on June 04, 2015, 08:56:10 am"Currently most of our long-distance transmitters/transmitting modules are not FCC/CE certified. Most super-regenerative receiver units aren’t applied for FCC/CE certification. Some OOK super-heterodyne units can reach FCC/CE requirements, normally their range is less than 100m. Most of FSK pairs have excellent performance and they meet FCC requirements, the maximum range can be more than 200m."Straight from their website (from your first URL). Just in case the OP cares...cheers,george.

author: eneuro
author_rank: Super Contributor
timestamp: June 04, 2015, 10:53:41 pm
content: Quote from: bookaboo on June 03, 2015, 03:16:29 pmProbably it will depend on requirements of how many bits per second we expect to haveTried those cheapy 433MHz $2 modules and got... at nice sunny day 350m blinking at 1Hz 50% PWM with transmiter aka dipole but only ~1.5m above ground and reciver in hand ~1 above ground, additionaly there were no perfect view between transmiter and receiver, so this what I get gone far above my expectations and will test transmiter powered at 10V, since they claim its operating voltage 12V, but I'd like to power it from car starter battery 12V without any boost-buck DC-DC converters for the moment.Note: transmiter was "dipole"m but receiver had quater wavelength antena ~164 mm -both powered @ 5Vcc with small MPU driving transmiter data pin.Didn't tested yet how many bits per second can send with thi setup and plot those numbers vs distance between those RF modules.Anyway, for my lawn tractor looks like those modules will be fine and trying to figure out howto configure modules like those as network of repaters to cover bigger area-I'm thinking of it as failure backup nodes-if one fails, another still can "repeat" RF signal and send to other in his range, so to have something like failure tolerant solution-one RF module failure doesn't shutdowns whole RF comunication system

author: hendorog
author_rank: Super Contributor
timestamp: June 05, 2015, 09:49:07 am
content: http://www.aliexpress.com/store/product/RFM95W-868-915S2-ultra-long-range-lora-module/1392412_2020357195.html

author: autobot
author_rank: Regular Contributor
timestamp: June 07, 2015, 11:24:45 am
content: LoRa is a good fit for that.There are also some mbed libraries for it, making development easy.

author: Psi
author_rank: Super Contributor
timestamp: June 07, 2015, 12:24:42 pm
content: A $20 433mhz RC airplane transmitter will go that far without problems.a OpenLRS clone for example. And its open so you can hack it

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 07, 2015, 03:23:33 pm
content: Quote from: free_electron on June 03, 2015, 04:02:19 pmhttps://www.google.com/search?q=loRa&client=opera&hs=nIe&tbm=isch&tbo=u&source=univ&sa=X&ei=7V90VfPhH8jFmAWczYL4Dg&ved=0CEQQsAQsadly even the SX1272 is stated as "long" range, how "long" is anyone's guess.

author: Neganur
author_rank: Unknown
timestamp: June 07, 2015, 07:50:30 pm
content: You should be able to get +20dBm output on the PA_BOOST output with a stable power supply (i.e. no longer just low power, >2.4V and some 100mA).With a proper antenna, some claim 10 miles / 16 km line of sight and some 3 miles / 2 km inside buildings.You can increase sensitivity by using a split path for rx/tx, large spreading factor and narrow bandwidth. Surely 2 km should not be a problem.

author: eneuro
author_rank: Super Contributor
timestamp: June 07, 2015, 10:11:29 pm
content: Quote from: Neganur on June 07, 2015, 07:50:30 pmYou are talking about 100mW transmiters or 1W for those a few km ranges?Flite testbelow, but 2 years ago, however mention also OpenLRSI was testing those cheapy $2 modules I've linked above with GPS and than calculated distance between transmiter and receiver from GPS log data.Tomorow 10V transmiters test with dipole vs quater length antenas.Trying to figureout what range we can expect from 100mW 433MHz transmiter with decent antena and what power needed for a few km ranges ?

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 08, 2015, 01:53:25 am
content: Is modding (or even just connecting to the headset jack) a pair of cheap walkie talkies an option?

author: niekvs
author_rank: Contributor
timestamp: June 08, 2015, 07:51:37 am
content: QuoteYou can see some LoRa range testing here:https://www.cooking-hacks.com/documentation/tutorials/extreme-range-lora-sx1272-module-shield-arduino-raspberry-pi-intel-galileoSo a line-of-sight distance > 20km, and around 2km a urban areas.This was using 868MHz, but 433MHz should generally reach further still - and they seem to be done at 15dBm, while most SX1276 modules seem to max out at 20dBm, so they should theoretically reach further as well (though a lot depends on their design, etc.)

author: eneuro
author_rank: Super Contributor
timestamp: June 08, 2015, 09:57:47 am
content: Quote from: niekvs on June 08, 2015, 07:51:37 amThx, for this link. That is interesting 20km LOS using only 25mW transmiter power?It looks like they use quater wavelength antenas with those LoRa modules-but what about using classic half wavelength dipole antenas with this sort of things?Is it possible and any benefits?However, we are talking a low data-rate down to few bytes per second ONLY in those LoRa modules?It will be interesting if those cheapy $2 433MHz modules powered at 10V will be capable to deliver a few bytes per second transfer rate at 1km range with good antenas?I had already 350m NLOS but it was only ~1Hz 50% pwmhttp://www.icstation.com/433mhz-transmitter-receiver-arduino-project-p-1402.htmlThey says:Transmitting power: 10mWProbably they specified there maximum when transmiter powered from 12V

author: Neganur
author_rank: Unknown
timestamp: June 08, 2015, 11:19:57 am
content: Quote from: eneuro on June 07, 2015, 10:11:29 pmHave you read any of the data sheets?I can't see your region, but +14dBm (25mW) is for ETSI 868MHz and with a 3dBi antenna you'll easily transmit 8km. The greater power +20dBm can be used for FCC 915 MHz and should give you some 13 km range with the same antenna type.For example Multitech has a module called mdot, it's meant to work with the mbed stuff.

author: RupertGo
author_rank: Regular Contributor
timestamp: June 08, 2015, 04:26:22 pm
content: I've seen something similar done with unmodded walkie-talkies and a couple of boxes. One injected one of a selection of tones via the microphone socket and toggled the PTT line, the other listened to the headphone output and toggled lamps according to tones heard.Or you could just put a walkie-talkie at each station and tell the teams to call in once they get there

author: Unknown
author_rank: Unknown
timestamp: February 27, 2017, 11:30:10 pm
content: Quote from: tggzzz on June 03, 2015, 02:33:54 pmSpeaking of which, rather than trying to build this in unlicensed bands, why not just pick up a HAM license and build it there? A lot of the regulatory, interference, and power output concerns just go away.There are a lot of existing cheap circuit designs and products for embedded TNCs, APRS, etc. Although, admittedly not as cheap as the ultra low power unlicensed UHF modules. For using that low power stuff, I would use as much gain as you can reasonably get (e.g. a yagi or, at 900MHz and above, a panel antenna). Antenna gain has much more to do with path length than power levels. You may also try operating at different polarization than other users of the band (e.g. horizontal vs. vertical polarization) if you are concerned about interference from other uses (team voice comms, etc.).

author: BrianHG
author_rank: Super Contributor
timestamp: February 28, 2017, 03:49:08 am
content: I've used this guy:https://www.alibaba.com/product-detail/universal-3km-433-cheap-rf-module_1809987082.html?spm=a2700.7724838.0.0.r8Q13YFor RX, i used:https://www.alibaba.com/product-detail/315-433MHZ-RF-ASK-Receiver-Transmitter_2005979852.htmlIt's a little over powered for 1km, but, dirt cheap and functional (I tried it...) with most of the cheap 2-3$ superhert receivers.In the city, it should give you 1km, outside of the city, about 2.5km.Going through the concrete walls of my house + through 15 other houses + some help from reflections, you will get around 0.5km. See attached photo. The white ring is 0.5km.Remember, there is a lot of traffic on the 433 Mhz band since it is use by so many gadgets. You need good MCU code to drive it and decode on the other side to deal with all that random interference in the city, but it is very doable since you got that 3watt burst during transmit.2 notes, your transmit data pulses shouldn't exceed 50% duty cycle, or it will overheat. The data in will work with a full clean 3.3v, preferably 5 v signal. The power supply needs 12v. It comes with a tuned antenna. I recommend modulating your transmit data with a carrier like an IR remote control signal so your receiver on the other side can use your carrier frequency to demodulate the data differentiating it from surrounding noise and interference,..All those red arrows are the houses the signal had to go thru to reach my receive location. Out in a flat open area, or, having the transmitter high up, you should get at least double the distance I got in my suburb test. I was transmitting a 4Khz test carrier through the transmitter & testing the receiver at the other end.I requested a quote for 5 from this guy: (Even though he says 200pcs minimum, he still sold me 5, + 5 receivers)TXhttps://www.alibaba.com/product-detail/universal-3km-433-cheap-rf-module_1809987082.html?spm=a2700.7724838.0.0.r8Q13YRXhttps://www.alibaba.com/product-detail/315-433MHZ-RF-ASK-Receiver-Transmitter_2005979852.html?spm=a2700.details.maylikever.10.697a8c3epkWsf4

author: mubes
author_rank: Regular Contributor
timestamp: February 28, 2017, 08:37:22 am
content: Deffo LoRa (you don't need the loRaWAN bit). SX1272 or SX1276. Their range claims are not bs. There are plenty of breakout boards with built in antennas at the usual places.Dave