- 易迪拓培训,专注于微波、射频、天线设计工程师的培养
ads dbmtov expression
This is the expression used by ads to convert dbm to V, can anyone shed some light on where the 8 comes from.
Example:
y = dbmtov(10 (power) , 50(Zref))
returns 2.0
Expression:
value = ( 8 * (10^((v(power)-30)/10) ) * R(Zref) )^1/2
from my hand calculation, I always get value = 1 based on input power of 10dBm and reference of 50 ohm.
Thanks a lot
It is because dbmtov(power_dBm, Zref) converts the dBm measure into open circuit voltage, Vemf_peak(peak value not rms value), given the reference impedance.
power_Watt=(Vemf_peak/(2*sqrt(2)))^2/real(Zref)=Vemf_peak^2/(8*real(Zref))
power_dBm=10*log10(power_Watt)+30
power_Watt=10^((power_dBm-30)/10)
Vemf_peak=sqrt( 8*real(Zref)*power_Watt )=sqrt( 8*real(Zref)*10^((power_dBm-30)/10) )
Hi Panchoo,
Thanks, but this is the part which I still eludes me, the 2 as shown:
power_Watt=(Vemf_peak/(2*sqrt(2)))^2/real(Zref)=Vemf_peak^2/(8*real(Zref))
^
|
|
I understand that,
Vrms = Vpeak/sqrt(2), but why is the 2 there?
Thanks
PS:
Hi Pancho,
I wanted to highlight the 2 but the arrow spacing is off
power_Watt=(Vemf_peak/( 2 *sqrt(2)))^2/real(Zref)=Vemf_peak^2/(8*real(Zref))
I understand that,
Vrms = Vpeak/sqrt(2), but why is the 2 there?
Thanks
Again, dbmtov(power_dBm, Zref) converts the dBm measure into open circuit voltage, Vemf_peak(peak value not rms value), given the reference impedance.
Red is because Vemf_peak is open circuit voltage.
Blue is due to conversion of Vemf_peak/2 to RMS value.
Hi pancho,
Yes I think I got it.... Thanks a lot!
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