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4b. Turn on the 4100 and set it to the same frequency, 520 kHz, using the FREQ SET key as
described in the PI 4100 Users Manual. The field strength reading should be in the neighborhood of 700
mV/m and the dc voltmeter reading should be in the neighborhood of 700 mV.
4c. Switch the generator RF output off or to its lowest level, or disconnect it, and check that the
4100 reading is below 1.0 mV/m. If the reading is greater because of an interfering signal, change the
4100 frequency just enough to reduce the interference well below 1.0 mV/m, and change the generator
frequency to match.
4d. Perform manual calibration of the 4100 (press and hold LPF until the word CAL in a box
appears, and wait until CAL OK appears).
4e. Switch the generator RF output on, returning its level to 700 mV. Check that the generator
and the 4100 are set to the same frequency. Readjust the generator output level for a dc voltmeter reading
of exactly 700 mV , or as close to 700 mV as possible. Record the 4100’s field strength reading in
mV/m and the dc voltmeter reading in mV.
4f. Repeat steps 4a thru 4e above for each test frequency.
5. Calculations and Report:
5a. If in 4e it was not possible to adjust the generator output for a dc voltage of exactly 700 mV,
calculate a corrected field strength value by multiplying the measured field strength by the quantity
[700/dcmV] where dcmV is the measured dc voltage. Use this corrected field strength value in the next
calculation.
5b. Calculate the per cent change in the measured (and corrected, if required) field strength value
from the value shown on the calibration certificate, as follows: (per cent FS change) = 100x[(FSmeas –
FScal)/FScal] where FSmeas is the value recorded in 4e or 5a, and FScal is the calibration certificate
value. If a measurement frequency is between two calibration certificate frequencies, estimate the FScal
value by interpolation.
Keep a copy of the completed data sheet with the calibration certificate for future reference.
6. Low-level tests:
For checks at lower signal levels a precision attenuator is needed such as are found in the better
modern signal generators. A convenient test is to increase signal attenuation in precise 10 dB steps while
observing the 4100 dBuV/m reading, which should also change in 10 dB steps. At each 10 dB step the
deviation from the ideal field strength value (a multiple of 10.00 dB below he starting value) should be no
more than 0.2 dB plus the attenuator error. The lowest level for which measurements are valid is
approximately 10 dB above the no-signal noise reading found in the measurement location. The ideal
location is a screened enclosure that reduces ambient radiated signals and noise to a low level.
7. RF In jack voltage measurement tests:
RF voltage measurements done by connecting a precision generator to the 4100’s RF In jack is
another way to evaluate measurement accuracy. This port has its own path into the receiver which
bypasses the antenna and most of the RF circuitry ahead of the mixer stage. The procedure is simply to
connect the generator directly or through a precision attenuator to the RF In jack, but a T-connector must
be used at the jack with an external 50 Ohm terminating resistor. The input resistance at the jack is 2500
Ohms. The RF voltage read on the display is typically within ±5 per cent of the input voltage, ± the
generator voltage accuracy.
This check can be done at an input level of 700 mV using the calibrate input detector to eliminate
generator level inaccuracy, as follows:
●Connect a BNC Tee connector to the Cal In jack; connect one side of the Tee to the generator
and the other side to the RF In jack.
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