Regulations as to encoding data over voice channel (443MHz, Belguim) - Page 1
Forum section: electronics / projects

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: October 27, 2015, 07:19:26 am
content: Hey fellow EE enthusiasts,tl;dr version: Am I allowed to encode digital data over a audio channel used in portable radios in Belguim? (freely available and legal to use portable radios)For a project I was looking at using "cheap" radios (the .5W radios in the 440MHz bands you can get and use without licence in belguim). EG:http://www.portofoonwinkel.nl/kenwood-tk-3501-protalk-portofoon/pid=32136I wanted to use them as a cheap quick radio that I know is "legal" and works. I would just encode the bitstream on the audiochannel. Seeing as some of the cheaper models come in at 20-25 euros a piece, I don't think I can build my own wireless system that can compete (I need very low datarates) at that cost.However, when I pitched the idea to someone on the internet, he told me I should watch out with encoding digital data into a voice channel. He told me that where he lives, this is not legal, since the channels are reserved for "voice" audio.Started looking on the internet, but couldn't seem to find a quick anwser to whether or not this is legal in Belguim. The reason I worry is because the end device will likely be used by someone in an official manner, so he has to be sure that his devices are not transmitting in reserved bands or in non-legal ways. Does anyone know/can anyone point me in the right direction for finding out? Reading through hundreds of pages of legal documents is not something I'm looking forwards to.

author: Gribo
author_rank: Frequent Contributor
timestamp: October 27, 2015, 02:04:01 pm
content: ETSI regulations allow digital transmissions in the 433.02 to 434.79MHz band. You are however limited to certain duty cycle and out of band emissions, which vary between different countries. If your channel is in the center of the band, low output power (max is 10dBm), and the modulation bandwidth is low, you shouldn't have problems.

author: boffin
author_rank: Unknown
timestamp: October 27, 2015, 04:55:52 pm
content: I know Garmin encode a small amount of data on transmit when a Garmin Rino transmits (so that other Garmin rinos are aware of the transmitter). IIRC they are limited to only making a data transmission every 30 seconds.

author: Howardlong
author_rank: Super Contributor
timestamp: October 27, 2015, 05:59:17 pm
content: Quote from: boffin on October 27, 2015, 04:55:52 pmEqually, ISTR that those radios aren't marketed in Europe, I always assumed due to regulatory reasons, but happy to be corrected. There are significant differences between the regs on licence exempt allocations between jurisdictions, not just with regards frequency allocations but also regarding modes of operation, emission modes, bandwidth, channel allocation and power.http://www.ti.com/lit/an/swra048/swra048.pdfmight be of help showing just how fragmented the regs are.

author: bktemp
author_rank: Super Contributor
timestamp: October 27, 2015, 06:59:13 pm
content: Quote from: TheUnnamedNewbie on October 27, 2015, 07:19:26 amYou say 443MHz, but the PMR from your link works at 446MHz. That is a different band!If a low datarate and 100-500m are enough, a small rf transmitter working at 433MHz or 868MHz is probably the cheapest and easiest solution, because it does all the modulation for you. There are many cheap transceiver modules or chipsets available working in the ISM bands. The cheaper ones using AM are dumb, you have to monitor the signal permanently for valid data yourself. The better ones use FM and do all the data slicing for you: You can put the data into a buffer and the module sends it without much processor overhead. At the receiver the data can be read from the buffer when the transmission has been received without any errors. RFM69 is one example for a cheap module working at 433MHz or 868MHz. Using 10mW it works over 100m (urban areas) up to 1000m (rural area with no obstacles in the line of sight).This should be valid for most countries in Europe:https://en.wikipedia.org/wiki/ISM_bandhttps://en.wikipedia.org/wiki/Short_Range_Devices

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: October 28, 2015, 10:36:16 am
content: Quote from: bktemp on October 27, 2015, 06:59:13 pmYou are correct, and this is bad use of terminology on my end. In a lot of forums/pages related to airsoft, where I often come into contact with these PMR devices in reviews/questions/... They are labeld as "the 440MHz band" even though that is not correct. From what I've seen, all the PMR's freely available around here that use the actual LPD433 bands and labeling and thus brands can be mixed to your liking.Which is also why I was looking at these devices - at events where the devices are used, we would then be able to say "band 1 to x is for staff only".Quote from: bktemp on October 27, 2015, 06:59:13 pmI've looked into these (at least a few) but, I need a higher range (300-400 meters in forest/urban areas) and the time I need to tack them together and get it to work reliably would not be worth it, I think I'd be better of buying radios - esp since the people hosting events will already have a dozen or so radios laying around so we would likely not even need to buy them.EDIT: after looking into the linked module, it seems like that one is a lot cheaper than the ones I've seen before (which would come in TX/RX pairs and cost 35-40 per pair, at which point a cheap radio costs less for me and provides the advantage of being able to switch channels and so on).Thanks for the help guys.

author: bktemp
author_rank: Super Contributor
timestamp: October 28, 2015, 04:53:19 pm
content: Quote from: TheUnnamedNewbie on October 28, 2015, 10:36:16 amSince LPD433 is restricted to the same 10mW as other 433MHz tranceiver modules, it does not have a higher range (<1km).The device (PMR446) from your link uses 446MHz where 500mW are allowed. This gives upto 10km range. I could not find any official document, but it looks like only voice is allowed in this band.Maybe the 868MHz band is a good choice, because it is less crowded.https://en.wikipedia.org/wiki/Short_Range_Devices#SRD860There are nice transceivers available for this band:http://www.semtech.com/wireless-rf/rf-transceivers/sx1272/At very low data rates they have a range of more than 10km.