Field strength meter

In telecommunications, a field strength meter is an instrument that measures the electric field strength emanating from a transmitter.

The relation between the electric field and the transmitted power

In ideal free space, the electric field strength produced by a transmitter with an isotropic radiator is readily calculated.

E

≈

30

⋅

P

d

{\displaystyle {\mbox{E}}\approx {\frac {\sqrt {30\cdot P}}{d}}}

where

E

{\displaystyle {\mbox{E}}}

is the electric field strength in volts per meter

P

{\displaystyle P}

is the transmitter power output in watts

d

{\displaystyle d}

is the distance from the radiator in meters

The factor

30

{\displaystyle {\sqrt {30}}}

is an approximation of

Z

0

4

π

{\displaystyle {\sqrt {\frac {Z_{0}}{4\pi }}}}

where

Z

0

=

376.730313668

(

57

)

{\displaystyle Z_{0}=376.730313668(57)}

Ω

{\displaystyle \Omega \quad }

is the impedance of free space.

Ω

{\displaystyle \Omega }

is the symbol for ohms.

It is clear that electric field strength is inversely proportional to the distance between the transmitter and the receiver. However, this relation is impractical for calculating the field strength produced by terrestrial transmitters, where reflections and attenuation caused by objects around the transmitter or receiver may affect the electrical field strength considerably.

Field strength meter

A field strength meter is actually a simple receiver. The RF signal is detected and fed to a microammeter, which is scaled in dBμ. The frequency range of the tuner is usually within the terrestrial broadcasting bands. Some FS meters can also receive satellite (TVRO and RRO) frequencies.