Miteq D-9301, Руководство по эксплуатации и обслуживанию, Страница: 35 / 86

4-1
SECTION 4
PRINCIPLES OF OPERATION
4.1 INTRODUCTION
The following paragraphs provide information on the principles of
operation of the MITEQ Model D-9301 Downconverter. Overall
functional operation of the system is discussed in Paragraph 4.2
and detailed principles of operation for the individual
subassemblies are presented in Paragraph 4.3.
4.2 FUNCTIONAL DESCRIPTION
The converter translates a 40 MHz frequency band at 3.7-4.2 GHz
to the 70 ±20 MHz output frequency band. A double conversion
system is used (see Figure 4-1).
The input signal is fed to an isolator and input filter which
rejects out-of-band signals including the image frequency. The
3.7-4.2 GHz signal is then converted in the first mixer to the IF
frequency by use of a synthesized local oscillator signal.
The output of the first mixer is fed to a low noise amplifier and
then to a filter which rejects out-of-band signals resulting from
the first conversion.
The signal is then fed to the converter module. The input signal
is fed to a mixer which converts the input signal to the output
IF frequency. The signal is then fed through a low pass filter,
which rejects the local oscillator signal, to a PIN diode
attenuator, providing gain control for the system, amplified and
output from the system. If Option 16 is ordered, an additional
amplifier is inserted between the filter and PIN diode
attenuator. If Option 2B is ordered a coupled output port is
included in the module to provide an IF test point at the rear
panel of the converter. If the converter is ordered with Option
5, the signal passes through a group delay equalizer which is
also included in the module.
The reference source for the local oscillator chains is a dual
output high stability oven-controlled crystal oscillator at 5
MHz.
The IF local oscillator is a phase locked source which is locked
to the 5 MHz reference.
The RF local oscillator is a synthesized frequency source which
is locked to the 5 MHz reference.