propagation through air ..

for LOS (line of sight) ... propagation through air can be modeled by FRIIS equation formula ...

this equation only counts for the distance between the tX and RX..

so for 2 antenna locating 1km away for example with LOS ...how can i measure the attnuation caused by air ...

imean i want to estimated the actual received power... is FRIIS formula sufficient for such a measurment?

ya this can be done

with friis equation u can measure it
or
u can use direct equation known as radar equation
read this



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yea...but the radar equation counts for the received power from the RCS of a far subject .. counts for reflection ?

is there anything estimate the air attenuation per km for example ? rain ? and other paramteres ?

because when i calculated the range for my transmitter the FRIIS said its 50 KM ? but idont think that it will reach this distance?


thanks again

The Friis formula should be corrected for many effectcs.
The propagation is function of many factors.
I.e.:
At mm wavelenghts, H2O and O2 absorption became remarkable.
At decameter wavelenghts, propagation is strongly dependent on ionosphere activity etc.
Many and very complicate models exist.

can u help me to find a channel model for 1 to 2.5 GHZ , for a LOS propagation ?

Don't you guys have google?

http://gbppr.dyndns.org:8080/longley.main.cgi

http://gbppr.dyndns.org/PROJ/mil/ew/urban.main.cgi

biff44.... the 2 links are blocked for connection from outside the USA ithink....however iopened them using anonymouse proxey;...
but the 2 models are not LOS models ithink ? theyre for urban city ?

The Friis transmission equation is the best way to define the free space propgation. You know the transmitted power and if u measure the recieved power u can calculate the total loss/attenuation.

The loss can be expressed in dB in the following form:-

L = 32.5 + 20 log R + 20 log F
note that the R is the distance is in km and F is the frequency in MHz.

U can find the detail of how to reach this formula in literature. Later on other effects can be added to this loss like attenuation, apsorption by layers etc. (as mentioned in the previous posts)

The model COST 231 - HATA is for urban areas yes in the range u wanted. If its straight LOS only and nothin more then thats perhaps the most simplest case of this model. Infact the Friis equation will do remarkably great in this case.