Helo!
I was just wondering if i want to make wireless transmission of sensor data for about 100 meters outside.How do i calculate needed transmission power and frequency.If i consider attentuation of around 20db from the outside environment.
thanks!
Frequency? Type of antenna?
Other factors include:
Heights of antenna above ground.
Moisture content of ground
Type of earth
Foliage in area
Hills, cliffs, …
There are predictive models available but from experience they can be off as much as an order of magnitude in both directions.
zyberb;
Look up “RF Link Budgets.” There should be plenty of information available on the internet on this topic.
In a nutshell, You need to calculate the loss over your 100m transmission path (you can guess “free space” path loss to make it really easy, or you can apply other formula/algorithms depending on the frequency you chose terrain you’ll transmit over), figure out what your fade margin will be for rain/temporary obstructions, etc etc, figure out your Rx sensitivity, Rx antenna gain, Tx antenna gain and some other variables (depending how detailed of an estimate you want), from which you can calculate the required power.
Frequency choice would be based on less calculated factors… I.e. availability of bands, congestion in bands, type of propagation you want (Though assuming at only 100m, you’re not really going to be using ground or sky wave propagation), and difficulty of implementation of various frequencies.
Re frequency - the lower the frequency, the longer your range will be. This is mainly due to lower propagation loss for lower frequencies, but receivers also tend to be more sensitive at these frequencies.
VHF is capable of giving very good range, if you can deal with bandwidth / licensing issues etc (as applicable to whatever country you’re in).
2.4GHz is obviously very popular, but it can be difficult to get decent range. I’m using Atmel’s AT86RF212 chips (in the 900MHz band) for a project, since (on paper at least) they are capable of much better range than 2.4GHz solutions at the same power level.
zyberb:
Helo!I was just wondering if i want to make wireless transmission of sensor data for about 100 meters outside.How do i calculate needed transmission power and frequency.If i consider attentuation of around 20db from the outside environment.
thanks!
with a line of sight situation - yes. It’s simple math plus knowing the transmitter’s power, receiver’s sensitivity for a given bit error rate, and in some cases, antenna height.
google Link Budget calculation spreadsheets