reconfiguration in the swip-generator swing band; start of frequency meter; setting the
transmission ratio of the controlled amplifier; detectors sub-band installation;
indication of measurement results and operating modes of the device.
Figure 1.1. Frequency characterograph diagram.
Due to the information about the level of the output signal from the attenuator, the
frequency of the output signal from the frequency meter and the level of the measured
signal from the detector, the calculation of the parameters of various frequency
characteristics of the studied four-pole is carried out. In this case, the linearization of
the frequency scale and correction of the unevenness of its own frequency
characteristic performs too, that increases the accuracy of the measurement. For
operating at low signal levels in order to reduce noise and interference a multiple
sampling mode and averaging of measurement results is used.
Series spectrum analyzers (Fig. 1.2) are a common type of panoramic devices
using for signal analysis. The principle of their work is to scan the frequency band with
the help of a controlled oscillator or swip-generator. The components of the spectrum
transfers to an intermediate frequency one by one. The selective node in the form of a
series-connected intermediate frequency filter and logarithmic amplifier consistently
allocates the components of the spectrum, they detects and, due to to synchronous
sweep, the responses of each spectral component are sequentially reproduced on the
computer monitor.
Panoramic receivers, in contradistinction to spectrum analyzers, have a previous
selective amplifier. Therefore, their sensitivity is much higher. They also include
additional nodes for demodulating of any signals. The panoramic receiver, as well as
spectrum analyzers considered above, has a controlled, sweep-generator based
oscillator.
Among the known methods of determining the frequency of the sweep-generator
were distinguished the following.
swip-generator
attenuator
investigated
four-pipe
controlled
amplifier
frequency
meter
microcontroller
ADC
detector
indication
block
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