# Conversion Formulas. ETS-Lindgren 3160

90 Pages

The losses of the coaxial cable, A c

, should be included in the computations. In this case, the previous equation becomes:

RF Voltage, dB(µV) + Cable Loss, dB +

Antenna Factor, DB(m

-1

) = Field Strength, dB(µV/m)

E a

= V a

+ A c

+ AF

Conversion Formulas

Following are some useful conversion formulas, including how the constants are obtained:

E

QUATION

1

dBm=dB(  V)-107

The power is related to the voltage and the system impedance as:

P

V

2

R

In a 50 Ω system, the previous equation becomes:

10 log

10

P

 20 log

10

V

 10

10

Converting from dB to dBm for power and from dB(V) to dB(

µ

V) for voltage, the overall constant becomes:

10

  107

44

E

QUATION

2

dB(mW /m

2

) = dB(  V/m)-115.8

The constant in this equation is obtained by considering the

Poynting vector which relates the power density in (W/m

2

) to the electric field strength in (V/m) by:

P =

E

2

Where

η

is the free space characteristic impedance equal to 120

π

Ω.

Transforming the previous questions to decibels and using the appropriate conversion factors to convert dB(W/m

2

) to dB(mW/m

2

) for power density and dB(V/m) to dB(µV/m) for the electric field, the constant becomes: log ( 120

)   .

E

QUATION

3

dB(  V/m) = dB(  V) + AF

E

QUATION

4

V/m = 10

20

E

QUATION

5

dB (  A/m) = dB(  V/m) - 51.5

The magnetic field strength is related to the electric field strength via the characteristic impedance of free space. When the transformation is made to decibels, the constant becomes: www.ets-lindgren.com Radiated Emissions Measurements

45

20 log ( 120

)  51 5

E

QUATION

6

A/m = 10

20

E

QUATION

7

dB(W/m

2

) = 10 log (V/m

A/m)

E

QUATION

8

dB(mW/m

2

) = dB(W/m

2

) + 30.0

E

QUATION

9

dB(pT) = dB(  A/m) + 2.0

The magnetic flux density B in (T) is related to the magnetic field strength H in (A/m) by the permeability of the medium in (H/m). For free space, the permeability is o

= 4

-7

H/m. Converting from (T) to (pT) and from (A/m) to (

µ

µ π

.10

A/m) and taking the log, the constant becomes:

4

 10  7 

46

### Key Features

• Frequency range: 30 MHz to 1 GHz
• Gain: 12 dBi to 15 dBi
• 3 dB beamwidth: 90 degrees in both the E-plane and H-plane
• Lightweight and easy to handle
• Rugged construction
• Resistant to corrosion
• Versatile