Day/evening coverage
Day/evening coverage
(OP)
I have an application requiring two-way RF data communication at a location in Southern United States.
I am operating 1mW at abotu 900MHz. Communication over a short range (few hundred feet) can be difficult during the day, however, at night the range is far more than required.
Any clues as to why this may happen. Is it synomonous with the day/night transmission of the lower bands (CD and AM radio), where AM radio transmitters in Canada must actually be directed north during the night? Can anybody explain this?
I am operating 1mW at abotu 900MHz. Communication over a short range (few hundred feet) can be difficult during the day, however, at night the range is far more than required.
Any clues as to why this may happen. Is it synomonous with the day/night transmission of the lower bands (CD and AM radio), where AM radio transmitters in Canada must actually be directed north during the night? Can anybody explain this?





RE: Day/evening coverage
I suppose that the mentioned effect has its reason in manmade noise which is quite a lot higher during daytime than at night. High speed LANs and WLANs, computer equipment, wireless communication equipment and such modern gear raise the noise level. Most people stop working at night. Watching the noise level with a spectrum analyzer will show this.
Many receivers of data communication equipment have very broad input stages. So if some other wireless communication equipment is operating in the same area, even its transmitting frequency is quite different, it will lower the sensivity of your equipment. This could be prevented by using good filters between antenna and the data-transceiver with a high selectivity.
Just a small story from my job department: A guy who is working with me bought a new car which has a small key-chain remote control to open the cars doors. This remote control is working on 433MHz. Another guy from my department is a ham who started transmitting on 439MHz to make a little joke when the car-owner tried to open the car to drive home. The car did not open its doors! He was very astonished and we had something to smile about.
RE: Day/evening coverage
Common interference at this frequency is from cell phone towers in the 800-890 MHz range, 930-950MHz range, and cordless phones which share the same band.
Also look for something which might be changing in the near/direct path between your devices - i.e. a large metal garage or bay door which closes as business shuts down in the evening, Fence gate, semi truck/trailers being parked, etc. You don't have much path margin to fool around with.
RE: Day/evening coverage
We have other versions of this device that operate at about 870MHz. Due to the Cellular band, we cannot use them in North America. As you would expect, the cellular interference swaps us.
The receive device actualy has a low noise floor at -100 dBm.
Iden
RE: Day/evening coverage
If you make a walk with a friend on the beach during storm and the waves are rolling towards the coast you have a very limited range if you just talk with normal volume to your friend. During silence (the sea is calm and "looks like a mirror") your friend will be able to go away several meters and will still understand what you are talking about...
RE: Day/evening coverage
I know they may be overkill for your application but here are some RF link papers to refer to:
http://www-classes.usc.edu/engr/ee- ep/475/Radio_link_design.pdf
http://mendel.ee.washington.edu/rainfall/lec10.pdf
http://staff.aub.edu.lb/~webfea/courses/EECE503/Handout%207%20-%20Cellular%20coverage-1.doc
RE: Day/evening coverage
RE: Day/evening coverage
I would like to add one more point of view. Antenna used i such a device is always pointed, in some way, towards the ground. And, as everybody knows, it gathers the thermal noise from the ground. During the night situation is much better. To avoid such a problems You have to make good design on RX side ( low noise, filtering, etc..
Other conclusions from above posts are also correct and it is very hard to estimate what has the biggest influence. The best way is to take Your equipement and test it in totalt different enviroment.
Good luck,
Buding.