Operating instructions

OPERATING MANUAL 2945A

46882-311D 3-59

When operating in the Look and Listen mode, some functions or options of SPEC ANA mode

will be available to the user. Reference to these is made on the display but their condition cannot

be changed without returning to the main spectrum analyzer display. These are:-

Reference level dB/div 2 dB 10 dB

Video filter option OFF ON

Peak hold option OFF ON

Input sensitivity

The input sensitivity of the Service Monitor in the Look and Listen

mode is the same as for the

normal spectrum analyzer input. The reference level can be set using the data input keys, or

adjusted using the variable control. The LEVEL [

] and [ ] keys adjust the reference level in

either 2 dB or 10 dB steps depending on the setting of the reference level vertical range.

Making measurements

The monitor can be used to determine the frequency of a transmission and to identify the

modulation type and content of asymmetric transmissions. When the transmission to be

examined is visible on the display, adjust the centre frequency line on the display to coincide with

the peak of the signal. This will be the carrier frequency and will be shown as a digital readout.

Progressively reduce the span and optimise the filtering and demodulation method while listening

to the demodulated output. As the span is reduced the centre frequency may need optimising.

The peak level of the signal can be determined by reference to the RF level scale on the display.

The top of the graticule represents the reference set on the display. Each division of the graticule

represents either 10 dB or 2 dB, as set in the vertical scale setup menu of the main SPEC ANA

mode.

AF test (audio frequency testing)

Overview

COUNTER

TONES

GEN

OUT

DIST-

ORTION

METER

VOLT-

METER

SERVICE

MONITOR

AMPLIFIER UNDER TEST

FILTERS

C3380

Fig. 3-17 Audio test setup.