RF Output power (dBm) v/s Distance (mtr)

[leo.dipen]

Hello !

In regards to RF communication and more specific to RF Modules, I need an approximate relation between the Transmitted Output Power (in dBm) and the Distance (in meter), the o/p power corresponds to.

Almost all datasheets simply express the output power in dBm.

I'm looking for a RF module that communicates over a distance of 100 meters, through walls &/ or obstacles. Suggestions/ weblinks for such RF transceiver modules for a low cost solution, will be appreciated.

--Dipen

 

[alexxx]

If we are talking about 2.4GHz band, you will have a hard time finding such wide indoors range. Also let's not forget that for indoors range, the receiver sensitivity is propably most important than transmitting power.
You will need an amplified signal, but +20dBm (100mW) is the best you can get. Higher output power is law forbidden for this band.
As for meters, I think that meters are given within specifications, but only for outdoors and under specific circumstances.
For indoors things get more complicated, like what is the building's constructing material? Metal is one thing and wood is another...

Alexandros

 

[leo.dipen]

Thanks Alexandros. Those are valuable inputs. I agree with you to the fact that I'm indeed having a hard time finding such a module.

But how about the RF modules in the 868 MHz range? To the best of my knowledge, the 865 MHz to 867 MHz band is freely usable in my country, i.e. India. Also, what is the maximum output power transmittable in this 868 MHz band that the law allows?

-- Dipen

 

[leo.dipen]

Hello !

As per the National Frequency Allocation Plan 2011, the following frequencies are freely usable in India

Use of low power RFID equipments or any other low power wireless devises or equipments in the frequency band 865-867 MHz with a maximum transmitter power of 1 Watt (4 Watts Effective Radiated Power) with 200 kHz carrier band width has been exempted from licensing requirement. ( see also GSR 564 ( E) dated 30 July 2008)

AND

Use of low power equipments in the frequency band 2.4-2.4835 GHz using a maximum transmitter output power of 1 Watt (4 Watts Effective Radiated Power) with spectrum spread of 10 MHz or higher has been exempted from licensing requirement (see also GSR 45E dated 28.1.2005)

The document can be downloaded via --- **broken link removed**

That answers my question !! :-D

-- Dipen

 

[Ashish_Sahay]

Hi Dipen,

I fail to understand how does it addresses your initial problem "RF module that communicates over a distance of 100 meters, through walls &/ or obstacles. Suggestions/ weblinks for such RF transceiver modules for a low cost solution"?

Await your suggestion.

Ashish