A.H. Systems AK-571-4 Betriebshandbuch - Seite 11

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A.H. Systems AK-571-4 Horn Antenna Kit

ANTENNA FORMULAS AND CALCULATIONS

EMISSIONS TESTING

Individual calibration data for the log periodic antenna is supplied at appropriate

distances (3, and 10 meter) to comply with various emissions test requirements.

For emissions measurements, add antenna factor plus cable loss to receiver

reading in dBV to convert to field strength in dBV/meter.

Field Strength(dBuV/m) = SA(dBuV) + AF(dB/m) + cable loss (dB)

IMMUNITY TESTING

For Immunity measurements, the generated electric field strength can be

calculated by:

The constant in the above equation is derived as follows. Power is related to voltage according to

Ohm's law. The Log

Note, the resistance of 50 used above reflects that RF systems are matched to 50

systems use decibels referenced from 1 mW, the corresponding voltage increase for every 1 mW

The logarythmic form of Ohm's law shown above is provided to describe why the log of the

 A.H. Systems inc. – Apr 2020

REV C

SA = Spectrum Analyzer or Receiver voltage reading

AF = Antenna Correction Factor

CL = Cable Loss in dB

FS = Approximate Field Strength in (V/m)

P = Power in watts

g = Numeric Gain

d = Distance in meters

Common RF Related Conversion Factors

function is used for relative (dB) scales, so applying the logarythm function to

Ohm's law, simplifying, and scaling by ten (for significant figures) yields:

10Log

power increase can be calculated with another form of Ohm's law.

V = (PR)

Given a resistance of 50and a power of 1 mW

20Log

corresponding voltage is multiplied by 20.

dBmW = dBV - 107

P = V

/ R

[P] = 20Log

[V] - 10Log

= 0.223 V = 223000 V

0.5

[223000 V] = 107 dB

[50



]



. Since RF