A.H. Systems SAS-585 Standard Gain Horn Antenna
©
A.H. Systems inc. – June 2014
REV A
11
TYPICAL CONVERSION FORMULAS
LOG -> LINEAR VOLTAGE
FIELD STRENGTH & POWER DENSITY
dB
V to Volts
V = 10
((dB
V – 120) / 20)
dB
V/m to V/m
V/m = 10
(((dB
V/m) -120) / 20)
Volts to dB
V
dB
V = 20 log(V) + 120
V/m to dB
V/m
dB
V/m = 20 log(V/m) + 120
dBV to Volts
V = 10
(dBV / 20)
dB
V/m to dBmW/m
2
dBmW/m
2
= dB
V/m – 115.8
Volts to dBV
dBV = 20log(V)
dBmW/m
2
to dB
V/m
dB
V/m = dBmW/m
2
+ 115.8
dBV to dB
V
dB
V = dBV +120
dB
V/m to dB
A/m
dB
A/m = dB
V/m – 51.5
dB
V to dBV
dBV = dB
V - 120
dB
A/m to dB
V/m
dB
V/m = dB
A + 51.5
LOG -> LINEAR CURRENT
dB
A/m to dBpT
DBpT = dB
A/m + 2
dB
A to uA
A = 10
(dB
A / 20)
dBpT to dB
A/m
dB
A/m = dBpT – 2
A to dB
A
dB
A = 20 log(
A)
W/m
2
to V/m
V/m = SQRT(W/m
2
* 377)
dBA to A
A = 10
(dBA / 20)
V/m to W/m
2
W/m
2
= (V/m)
2
/ 377
A to dBA
dBA = 20log(A)
T to A/m
A/m =
T / 1.25
dBA to dB
A
dB
A = dBA + 120
A/m to
T
T = 1.25 * A/m
dB
A to dBA
dBA = dB
A -120
E-FIELD ANTENNAS
LOG -> LINEAR POWER
Correction Factor
dB
V/m = dB
V + AF
dBm to Watts
W = 10
((dBm – 30)/10)
Field Strength
V/m = 30 * watts * Gain
numeric
meters
Watts to dBm
dBm = 10log(W) + 30
Required Power
Watts = (V/m * meters)
2
30 * Gain
numeric
dBW to Watts
W = 10
(dBW / 10)
LOOP ANTENNAS
Watts to dBW
dBW = 10log(W)
Correction Factors
dB
A/m = dB
V + AF
dBW to dBm
dBm = dBW + 30
Assumed E-field for
shielded loops
dB
V/m = dB
A/m + 51.5
dBm to dBW
dBW = dBm - 30
dBpT = dB
V + dBpT/
V
TERM CONVERSIONS
dBm to dB
V
dB
V =
dBm + 107
(50
)
dB
V = dBm + 10log(Z) + 90
CURRENT PROBES
dB
V to dBm
dBm = dB
V – 107
(50
)
dBm = dB
V – 10log(Z) – 90
Correction Factor
dB
A = dB
V – dB
(ohm)
dBm to dB
A
dB
A = dBm – 73
(50
)
dB
A = dBm – 10log(Z) + 90
Power needed for injection probe given voltage(V) into
50
load and Probe Insertion Loss (I
L
)
dB
A to dBm
dBm = dB
A + 73
(50
)
dBm = dB
A + 10log(Z) – 90
Watts = 10
((I
L
+ 10log(V
2
/50))/10)
dB
A to dB
V
dB
V = dB
A + 34
(50
)
dB
V = dB
A + 20log(Z)
dB
V to dB
A
dB
A = dB
V – 34
(50
)
dB
A = dB
V – 20log(Z)
