Design & Test RF links - Page 1
Forum section: electronics / rf-microwave

author: Ralphy007
author_rank: Contributor
timestamp: July 06, 2021, 04:08:24 pm
content: I work in the Water Industry were we use radio links for telemetry/SCADA purposes. In order to find a viable link, a desktop study is completed using “path profile” applications which is backed up by an actual on site radio test. Any help in the form of webinars, paperwork or courses would be most welcome.The telemetry links are in the 460 MHz range, while some other SCADA sites would be in the range of a couple of GHzAt home, I use the Radio Mobile app. for path profiles which I believe uses the Longley Rice model.I am also wondering about the actual on site radio test and what measurements to take. I can calculate Fade Margin and I think 20 dB is a good target to aim for. I can also get figures for system availability/reliability and again, I think well over 99% is a good target to aim for ?Unfortunately I dont have any experience of doing this work and therefore want to be sure the figures I am getting are going to provide a link that is viable. Do you know of any documents/standards that I can refer to which give details on how to carry out the radio tests and what measurements to record etc.

author: 1design
author_rank: Regular Contributor
timestamp: July 06, 2021, 05:52:49 pm
content: I do something similar as part of my job in a different industry.The first question you need to ask is how will the links be used.What is the payload size and data frequency, how important is the data, can you miss packets, is the data UDP or TCP/IP type with an option to resend?99% is not a good reliability figure, carrier grade is six 9s, so 99.9999% reliability over the year. You might need a lot less, all depending on your use case.To do path planning I personally use SiteSync Pro from WAC as a quick and dirty start point and than move to Pathloss for a more detailed design.If the link has tight clearances it boils down to path surveys.A good book to point you in the right direction is this:https://www.walmart.com/ip/Microwave-Transmission-Network-Planning-Design-and-Deployment-Edition-2-Hardcover-9780071701228/102914711?wmlspartner=wlpa&selectedSellerId=8351&adid=22222222222093838955&wmlspartner=wmtlabs&wl0=e&wl1=s&wl2=c&wl3=75316614259183&wl4=pla-4578916192106817&wl5=&wl6=&wl7=&wl10=Walmart&wl11=Online&wl12=102914711_10000008576&wl14=Microwave%20Transmission%20Networks%20%3A%20Planning,%20Design%20and%20Deployment&veh=sem&msclkid=c77c5b2c859919264fd93bc81da6ed45&gclid=c77c5b2c859919264fd93bc81da6ed45&gclsrc=3p.ds

author: coppercone2
author_rank: Super Contributor
timestamp: July 07, 2021, 02:44:56 am
content: and also keep in mind that for some reason people keep targeting water for hacks (for some reason I imagine Augustus would disembowel you in the town square if you did this in ancient times by tampering with an aquaduct), so you might want to consider developing some security checks or at least tests to detect stuff thats off, or backup contingencies, it can prove electrically interesting to make over rides or what have you

author: Ralphy007
author_rank: Contributor
timestamp: July 07, 2021, 09:51:29 am
content: Many thanks for getting back. Interesting to hear you do something similar in a different industry.The water company I work for has a regional telemetry system which includes 10/20 basestations broadcasting to on average 90 outsations. The base station polls each outstaion in that region. If the outstation has data to report it uploads the data to the base station which in turn sends the data back (via micowave links) to central control.I am only interested in the comms. link between the base station and the outstation which operates in the region of 460 MHz. The regulatory authority in the UK is OFCOM who have reserved 80 channels (12.5 KHz) for water companies to use. I am not sure what the data type is and dont believe the payload is that big. I also do not believe the data is that critical as it only reports thinks such as plant status (pumps ON/OFF), flows amd levels. In fact when I started my career, a long time ago we did not have a telemetry system.I have some data from the system stating the reliability of 3 sites taken over various time scales i.e. 98%, 99.72% and 99.87%.I was wondering if there was a link between reliabilty and fade margin or received signal strength (rssi) ?It would also be helpful to know what a reasonable reliability figure would be for an industry such as Water.We could use this figure in contract documents to tell the contractor what to aim for when adding a new outstation to the telemetry system, instead of guessing or just turning up the power until reliable comms. was reached.I had a look at the book you recommended - very good. I may buy it

author: LaserSteve
author_rank: Super Contributor
timestamp: July 07, 2021, 01:24:09 pm
content: Utility service in the US is supposed to be Six Sigma, which works out to less then 15 minutes of hardware/fade failure per year.This is not for your / our UHF band, but is a good start for free:https://bryanfields.net/mw-papers/GTE%20Lenkurt%20Book.pdfIn the US, the 460 Mhz section is the high end of the Business / Commercial band, so plenty of on-line reading is available.12.5 Khz channelization works out to ~9600 Baud maximum, over here on the other side of the pond. More typically would be 2400 Baud.Steve

author: Ralphy007
author_rank: Contributor
timestamp: July 07, 2021, 04:05:41 pm
content: Some good info. in the old publication particularly with regard to availability / reliability.However still not sure if / how it is related to fade margin and what a reasonable number would be.