Function Principle; Circuit Description - Promax MC-360B Manuel

USER'S MANUAL. MC-360B

6 FUNCTION PRINCIPLE

6.1 Circuit description

Block diagram in Figure 4 shows the whole circuitry of the equipment.
Input signal is passing through a power divider that supplies a signal both to the
measuring system and to the RF output, allowing to use that signal with measurement
at the same time. Besides, at this stage, power is supplied to the external unit through
the RF input.
Signal is carried to that measurement circuitry suiting with the SAT or TV band
accordingly.
In measurements between 950 and 2050 MHz, signal is, at will, 0 or 20 dB
attenuated. After that, it passes to the tuner, where the selected frequency is converted
to 480 MHz. This signal, filtered accordingly, is applied to the detector circuit which
supplies a direct voltage in proportion to signal level.
Through the suitable converter, a linear rate is obtained, according to the signal
size logarithm.
The resulting signal is entered into the correcting circuit controlled by a
microcontroller, to modify reading according to signal level and frequency, in order to
minimize errors due to non-linearities or frequency response.
A sweep generator permits tuning system to be scanned in such a way that
band is watched throughout; the peak detector evidences any signal at the meter.
In 48 to 856 MHz measurements, signal is processed in a similar way. Main
differences are, for instance, those possible attenuation 60 dB, shared out in 40 dB at
the input, and in 20 dB next to the tuner.
The said component supplies a 38.9 MHz signal that, after passing through the
relevant converter, becomes a 10.7 MHz one.
Common parts to SAT and TV mode operations are the frequency meter and
the prescaler, as required at that input; the correction circuit and the audio amplifier
receiving that signal coming from the tone generator, or that signal obtained in both AM
or FM demodulators.
01/1996
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