RF power calculation

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arr_baobao

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Hi

I need to calculate the maximum RF power(dbm) from my device from the limit given in the picture below:
The device is 3m away and the limit is given in dB(μV/m).
Am i correct to used the llimit given multiple by 3 ( 3M away) then convert the dB(μV/m) value to dbm ?
 

Am I correct to used the llimit given multiple by 3 ( 3M away) then convert the dB(μV/m) value to dBm ?
Click to expand...
No. To calculate the field strength, you'll need to know the gain of transmitting antenna and put in free field impedance. See https://en.wikipedia.org/wiki/Dipole_field_strength_in_free_space

- - - Updated - - -

In case of a dipole transmitter antenna, you need about -57 dBm (2 nW) to achieve 40 dBµV/m @ 3m.
 


These limits are specifically given for spurious emissions and not for the carrier frequency.
 

BMR said:
These limits are specifically given for spurious emissions and not for the carrier frequency.
Click to expand...

Possible to calculate with addition of free space air loss to estimate the figure?
 

Free space loss formula gives you the received power with antennas of specific gain. Need to put in receiver antenna factor to calculate field strength. The approach quoted in post #2 calculates field strength directly.
 
FvM said:
Free space loss formula gives you the received power with antennas of specific gain. Need to put in receiver antenna factor to calculate field strength. The approach quoted in post #2 calculates field strength directly.
Click to expand...

Any link for free space loss formula for different frequency range?
thanks
 

Try this link **broken link removed**
 

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