ETS-Lindgren 3301B Active Rod & Field Antenna (Archived) - Manual (Page 39)

Calibration Procedure | 39
12.0 Calibration Procedure
ETS-Lindgren recommends the equivalent capacitance method of calibration for
the Model 3301B active rod antenna. To check the calibration, a Model 3301B
calibration test fixture is required. This fixture contains a resistive T and a
capacitor. The T allows for accurate reading of the input to the fixture. The
capacitor feeds the amplifier through the same impedance as the 41” rod
presents to it. The result is a simple, yet extremely accurate calibration.
Periodic checks of performance are recommended. To calibrate the unit, simply
attach the calibration fixture and ground it to the Model 3301B housing through
one of the counterpoise mounting holes. Place a signal source on one leg of the
fixture and a receiver on the other leg. Then terminate the output of the unit with
50 ohms. Read the input signal strength. The input signal strength measured
through the calibration fixture must have 11 dB added to it. The 11 dB is
composed of 6 dB required to normalize the rod to 1 meter and 5 dB of signal
loss through the resistive divider in the T. After the input is read, move the
receiver cable to the output of the unit and place a 50-ohm load on the now open
leg of the calibration fixture. Read the unit output. The antenna factor is the input
plus 11 dB minus the output, both readings assumed to be logarithmic.
ETS-Lindgren recommends the following input voltage levels for field calibration:
Voltage Internal Attenuation
250 mV 0 dB
450 mV 10 dB
8 V 30 dB
E XAMPLE
Suppose a reading is taken with a 1 MHz signal input to the calibration fixture.
The input is read as 50 dBuV and the output is read as 59 dBuV. The antenna
factor is then the input plus 11 dB minus the output of
50 dBuV + 11 dB - 59 dBuV = 2dB.
Archived 3/18/10