2.7. Design and Operation Overview
2.7.1. Principle of Operation
The TV Level Meter is a super heterodyne receiver with triple frequency conversion
(auto or manual frequency tuning). Channel power is measured by means of analog-to-
digital converter (ADC) after signal peak detection at output of logarithmic detector of the
amplifier of the third IF. The principle of spectrum analyzer is based on sequential analysis
method with spectrum indication on the LCD of the Meter or on PC.
The view displayed on the screen in the spectrum analyzer mode is the signal
frequency bar-graph. The mode of signal level measurement in a frequency point displays
the numeric value of the signal level, V/A and C/N ratios.
2.7.2. Block Diagram
The block diagram of IT-081 is shown in figure 2.3.
Figure 2.3
After the Low-Pass Filter (LPF), the input signal if necessary is reduced by the two
Attenuators (A1) and (A2). Then it is transformed into the first IF signal by the Mixer (M1)
and adjustable Local Oscillator (LO1). The first IF is 1216 MHz. Then the signal is passed
through the Bandpass Filter (BPF1). Local Oscillator (LO1) is implemented according to
circuit of the frequency synthesizer with phase lock loop.
The signal of the first IF is converted by the 1178 MHz Local Oscillator (LO2) and the
Mixer (M2) to the second IF, and is further filtered at 38 MHz frequency by BPF2. The
signal of the second IF is converted by the 27.3 MHz Local Oscillator (LO3) and the Mixer
(M3) to the third IF, and further filtered at 10.7 MHz frequency by BPF3, which defines the
receiver frequency band.
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