TB 9-6625-2221-24
IDENTIFICATION AND DESCRIPTION
1. Test Instrument Identification.
This bulletin provides instructions for the
calibration of Transmission Impairment Measuring Set, Hewlett-Packard Model 4945A.
The manufacturer's instruction manual was used as the prime data source in compiling
these instructions. The sound level meter will be referred to as the "test instrument"
throughout this bulletin.
a. Model Variations. None
b. Time and Technique. The time required for this calibration is approximately 2
hours, using the dc and low frequency technique.
2. Forms, Records, and Reports. Forms, records, and reports required for calibration
personnel at all levels are prescribed by TB 750-25.
3. Calibration Description.
Test instrument parameters
and
performance
specifications which pertain to this calibration are listed in table 1.
Table 1. Calibration Description
Test instrument parameters
Performance specifications
Receiver level
Range: -60 to +13
Accuracy:
-50 to +13 dBm (-60 to -50 dBm)
20 to 200 Hz r 0.5 dB (r 1.0 dB)
200 Hz to 15 kHz r 0.2 dB (r 0.5 dB)
15 to 110 kHz r 0.5 dB (r 1.0 dB)
1004 Hz holding tone r 0.1 dB from -20 to 0 dBm
Receiver frequency
Range: 20 Hz to 110 kHz
Accuracy:
For signal levels > -50 dBm at >20 dB
signal-to-noise ratio: 20 to 9999 Hz r 1 Hz
10 to 110 kHz r 10 Hz
Transmitter frequency
Range: 20 Hz to 110 kHz
Accuracy:
r 0.01% of output frequency
Holding tone:
1004 Hz r 0.1 Hz
Transmitter/receiver
>20 mA for applied open circuit voltages from 42.5 to 105 V dc
hold coil current
(either polarity through an external resistance of <1700 :)
(nominal 23 mA, 48 V, 1300 :)1
Transmitter level
Range: -60 to +13 dBm (600 :, 900 :, and 1200 :)
and flatness
-60 to +5 dBm (135 :)
Accuracy: -20 to 0 dBm at 1004 Hz, r 0.1 dB
-60 to +10 dBm at 1004 Hz, r 0.2 dB
1Checked
for >20 mA at +48 V only.
