Download Sharp R-309B Operating instructions

SECTION 4
CIRCUIT DESCRIPTION
The 10- MHz signal (± frequency e r r or )
is fed to the Second IF and Discr irninutor
board where it is amplified a nd m ixed with
a 9.9-MHz signal from the Multi-Osc illator
board to form a second IF"and 100 k Hz
(± frequency error). This second-IF s ig ­
nal is amplified and applied to the frequency­
error detector.
4.1 Introduction
The circuits of the Model CE-7 Multi­
Channel Fl\1 Communications Monitor are
on five printed circuit boards: the Second
IF and Discriminator board (0054), the
Power Supply board (0100), the Frequency
Error Meter board (010 1), the Harmonic
Generator board (0102), and the Multi­
Oscillator board (0103). Figure 4-1 is
the functional block diagram of the CE-7.
The 115-vac-supply fuse RP- F2, is on
the inside of the rear panel.
A squelch detector in the Broadband
Mixer or Preselector rectifies th e 10- i\IHz
signal. The resulting de voltage is ampli­
fied and fed to the signal-level detector in
the CE-7. If the 10-l\IHz signal exceeds
a preset level, the SIG:-\AL LEVEL lamp
lights to indicate that a cc urate me asure­
ments can be made and the frequencyerror detector is energized . The frequency­
error detector is adjusted to give a zero
indication on the FREQUENCY meter when
the second IF signal is exactly 100 k Hz .
If the frequency of the monitored signal is
above or below the frequency selected with
the CARRIER FREQUEf\'CY SELECTOR,
the input to the frequency-error detector
will be exactly the same amount above or
below 100 k Hz . The detector output will
cause the FREQUE~CY meter to deflect
toward the plus (+) or minus (-) side, in­
dicating the direction and a mount of fre­
quency error.
The CE-7 is basically a multi-channel
superheterodyne receiver and a signal
generator. In the FREQ. - DEV. MEASURE
mode of operation the RF signal, the fre­
quency and frequency deviation of which
are to be measured is applied through
the ANT. connector of the RF plug-in
that is being used (a Broadband Mixer
or one of the three Presel ectcr s) . The
RF signal is mixed in the RF plug-in
with the local-oscillator signal from the
Harmonic Generator board in the CE-7.
The local oscillator signal has a
frequency that results from mixing the
output of a selected crystal oscillator
(associated with the selected channel) with
the out put of a 10-MHz crystal oscillator.
When an R F signal must be measured for
carrier-frequency accuracy, the frequency
that has been assigned to the transmitter
of the RF signal is the same frequency
that is selected on the CE-7. Thus, the
CE-7 can only monitor a signal for which
it has a crystal of appropriate frequency.
If the monitored signal is frequency
modulated, the modulation will be present
in the output of the frequency-error detec­
tor. This output is demodulated and a sig­
nal representing the modulation is amplified
and fed to either the Model 302 FM Deviation
Meter or the Model 301 Oscilloscope. If
the Model 302 is used, its FM deviation
meter will indicate the peak deviation of
the FM signal. On the Model 301 Oscillo­
scope, the amount of deviation and frequency­
error will be shown on the CRT .
The incoming signal is mixed with the
internally generated "standard" or local­
. oscillator signal. If the transmitter of
the incoming signal is on-frequency, the
result of this mixing will be an IF of
exactly 10-MHz. If the frequency of the
incoming signal is not correct, the IF
signal will be 10 MHz plus or minus the
frequency error.
5601"0015
The CE-7 can be used as a C\V- or FM­
signal generator but its range i s limited to
the frequencies for which crystals are in­
stalled (if the Model l\1CO-6 Oven-Oscillator
is used, the range is extended to include the
auxili ary crystals).
4-1