What Causes RF signals to break during rain - Page 1
Forum section: electronics / beginners

author: vishal
author_rank: Regular Contributor
timestamp: June 05, 2017, 12:40:01 pm
content: HiWe are doing a project that collects sensor data and sends it to a central coordinator.The project uses the ZigBee-based custom board.We used avr-atmega256rfr2 MCU and downloaded the stack for it.But it's giving a different range in different location.Now the project running in a field of having lots of trees and plants.We read that the plants, trees, rain etc affect the RF signal.Are there any method to protect these signals from the rain.

author: sokoloff
author_rank: Super Contributor
timestamp: June 05, 2017, 01:02:10 pm
content: Water attenuates RF signals.That probably tells you that there's going to be nothing you can do to make your RF signal impervious to the effects of rain.

author: Benta
author_rank: Super Contributor
timestamp: June 05, 2017, 01:12:13 pm
content: Directional antennas might help, but need to be aligned correctly, of course. They will give you extra gain at both ends, but might only be possible at the sensor end, as the hub probably receives from all directions.

author: timb
author_rank: Super Contributor
timestamp: June 05, 2017, 01:13:21 pm
content: Quote from: sokoloff on June 05, 2017, 01:02:10 pmExactly. Otherwise Satellite TV companies would have long since done it. (Even moderate rain can completely interrupt "Mini Dish" satellite TV reception, due to the small dish sizes, small RF power levels and high frequency used.)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 05, 2017, 01:13:51 pm
content: Mostly absorption, yeah.I suppose there could be more reflection and absorption from surfaces, too, if they become conductive when wet (anything with a salty residue?).Depending on distance, there's also atmospheric inversion layers (relevant to >> 10km links), and ionospheric reflection (1000km+ links, shortwave band).Tim

author: coppice
author_rank: Super Contributor
timestamp: June 05, 2017, 03:12:02 pm
content: Absorption tends to rise quite rapidly with frequency. An FM radio antenna works really well in any weather in a loft space. Try that with a UHF TV antenna, and the signal will fade considerably when the roof tiles are soaking wet. Most people have to locate them outside. Radomes are coated in some really cool water repellents, which leave hardly any surface moisture, even in quite heavy rain.

author: David Hess
author_rank: Super Contributor
timestamp: June 05, 2017, 07:36:55 pm
content: The water just adds to the path loss in this case. Directional antennas will produce more operating margin and reject multipath so they help a lot with rain fade. Height to get above the foliage will help also. You might get better results in the 900MHz band but the antennas will be larger.

author: Tom45
author_rank: Frequent Contributor
timestamp: June 05, 2017, 07:47:46 pm
content: Your choices are one or more of:1) lower frequency2) higher power3) higher gain antennas4) protocol that uses error checking and re-transmitting (and/or error correcting redundancy)5) less rain

author: timb
author_rank: Super Contributor
timestamp: June 05, 2017, 08:56:11 pm
content: Quote from: Tom45 on June 05, 2017, 07:47:46 pmA very large tarp stretched between the transmitter and receiver also works well!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 05, 2017, 11:40:44 pm
content: Quote from: timb on June 05, 2017, 08:56:11 pmYou could support the tarp with something strong in tension, along the top center; something strong, like a steel cable... something conductive like a steel cable... Hey, I know!!Tim

author: cdev
author_rank: Super Contributor
timestamp: June 06, 2017, 11:47:50 am
content: It's likely conductivity that causes reflections and resistance that causes losses

author: Berni
author_rank: Super Contributor
timestamp: June 06, 2017, 12:57:05 pm
content: Quote from: T3sl4co1l on June 05, 2017, 11:40:44 pmYeah you could try sending the signal down the conductor.....hey wait you could also make the tarp out of conductive foil to shield other RF signals from getting in to the conductor to get a perfect transmission....oh wait someone already invented coax cable?

author: Vtile
author_rank: Super Contributor
timestamp: June 06, 2017, 04:04:11 pm
content: You mean leaky coax? Iirc Nokia(something) did it in 90s for better reception in build environments. I could remember falsely though.Scattering also rises in air-water transition surface.

author: Cerebus
author_rank: Super Contributor
timestamp: June 06, 2017, 11:52:30 pm
content: Quote from: timb on June 05, 2017, 08:56:11 pmIt's easier to replace the angry pixies normally used to provide motive power with Maxwell's daemons, which everybody knows are 10x more waterproof than angry pixies.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 07, 2017, 12:43:19 am
content: Quote from: Cerebus on June 06, 2017, 11:52:30 pmAnd not because they're hellishly hot or anything, as the name might suggest -- no, they're just small enough and fast enough to dodge the water molecules.Tim

author: floobydust
author_rank: Super Contributor
timestamp: June 07, 2017, 01:37:02 am
content: Check your TX power settings on the Zigbee module. Some default to middle power.Tree (plant) leaves also contain water, so in spring when tree leaves come out (in Canada), RF signal strength goes down.During winter when tree leaves fall off, RF signal strength is much better.Foliage can be a problem too.

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2017, 01:54:19 am
content: The RF characteristics of rain and storm droplets are pretty interesting. The differences in frequencies, polarization, and doppler shift that are absorbed and reflected are complex and informative. For example,dual polarization radarcan be used to tell if a storm is about to turn into a tornado.https://www.weather.gov/media/lmk/soo/Dual_Pol_Overview.pdfhttp://www.nws.noaa.gov/com/weatherreadynation/news/130425_dualpol.html

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 07, 2017, 02:09:45 am
content: In addition to all of the path losses from rain, you may also encounter problems in connectors and cables that are not adequately sealed or shielded. These losses continue for hours, days or weeks after the precipitation stops.

author: Berni
author_rank: Super Contributor
timestamp: June 07, 2017, 05:10:33 am
content: Quote from: CatalinaWOW on June 07, 2017, 02:09:45 amI actually seen coax cables work as a hose. Where there is something wrong at the antenna end and lets water get in to the coax where it then wicks itself all the way down the line until the connector at whatever the antenna is connected to is all wet and eventually coroded.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: June 07, 2017, 05:32:52 am
content: Quote from: cdev on June 07, 2017, 01:54:19 amNot quite. Can tell the shape of raindrops, which can be used to tell if the radar's looking at rain, hail snow or insects. (I work on this stuff for a living)To the OP: there are lots of causes, as others have pointed out. If you're using external antennas, it's because your they are wet. Consider a superhydrophobic coating, like WX2100:https://www.cytonix.com/WX2100-p/wx2100.htmThis stuff's pretty good, but needs reapplication once the surface is abraded by dust + high winds (UV degrades it too). If you're not using an external antenna, consider doing so.

author: jh15
author_rank: Frequent Contributor
timestamp: June 07, 2017, 05:37:09 am
content: Rent space to transmit dry under a local hyper loop.