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TM 11-6625-2872-14&P
3-17. 50 dB SPAN OPERATION.
3-18. Set the RANGE switch to the position which corresponds to the minimum expected signal level. See examples 1
and 2.
EXAMPLE 1: Minimum expected signal level 10 mnV rms. This corresponds to a -40 dBV signal level (see Table 3-1).
Set the RANGE switch to the -40 dBV position. The full scale signal level is 50 dB higher:
-40 dBV
add +50 dB
+10 dBV = Full scale input signal = 3.16 volts rms
EXAMPLE 2: Minimum expected signal level .5 volt rms. This corresponds to a -6 dBV signal level. Since there is no -
6 dBV switch position, set the switch to the next lower step, which is -10 dBV. The full scale signal level is 50 dB higher:
-10 dBV
add +50 dB
-40 dBV Full scale input signal = 100 volts rms
3-19. Set the RESP TIME/CAL DB switch to the FAST or SLOW position, depending on the signal bandwidth, and the
detection response) time desired. (For FAST response, the preamp) bandwidth is 500 to 100,000 Hz. For SLOW
response, bandwidth is 5 to 100,000 Hz.)
3-20. For 50 division chart paper, the calibration is 1 dB/div. The bottom division on the chart represents the bottom
scale signal level in dB indicated on the RANGE switch.
3-21. 100 dB SPAN OPERATION.
3-22. Only the four RANGE switch positions outlined in red (-80, -70, -60, -50) are used for the 100 dB span. Set the
RANGE switch to the position which corresponds to the expected minimum signal level.
EXAMPLE 1: Minimum expected signal is 1 mV rms. This corresponds to a -60 dBV level (see Table 3-1). Set RANGE
switch to the - 6OdBV bottom scale position. The full scale signal level is l00dB higher:
- 60 dBV
add +100 dB
+ 40 dBV = Full scale input signal = 100 volts rms
EXAMPLE 2: Minimum expected signal is
500 µV rms. This corresponds to a -66 dBV level. Set the RANGE switch to the next lower step, which is the -70 dBV
bottom scale position. The full scale signal level is 100 dB higher:
- 70 dBV
add +100 dB
+ 30 dBV = Full scale input signal = 31.6 volts rms
3-23. Set the RESP TIME/CAL DB switch to the FAST or SLOW position, depending on the signal blind bandwidth, and
the detection response time desired. (For FAST response, the preamp bandwidth is 500 to 100,000 Hz. For SLOW
response, bandwidth is 5 to 100,000 Hz.)
3-24. For 50 division chart paper, the calibration is 2 dB/div. The bottom division on the chart represents the bottom
scale signal level in dBV indicated on the RANGE switch.
3-25. OPERATION WITH MONITORING INSTRUMENTS.
3-26. When the preamplifier output is connected only to a monitoring instrument such as a dc voltmeter or oscilloscope,
perform the balancing (Section 3-9) and calibration (Section 3-11) procedure as indicated. Bottom scale output refers to
0 volts preamplifier output. Full scale output is -5 volts preamplifier output. The 50 dB span calibration is .1 volts/dB.
The 100 dB span calibration is .05 volts/dB.
3-27. SIMULTANEOUS RECORDING AND MONITORING OF 8808A OUTPUT.
3-28. To simultaneously record and monitor the 8808A output signal, perform the balancing and calibration procedure
using the recorder. The dc voltmeter, oscilloscope, or other monitoring instrument connected to the output of the preamp
will read approximately -2.5 volts for a bottom scale input signal, and approximately +2.5 volts for a full scale input
signal. The monitor instrument calibration is .1 V/dB on the 50 dB span, and .05 V/dB on the 100 dB span.
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