Operating instructions

TECHNICAL DESCRIPTION
4-13
Rx test mode
The Rx TEST mode requires a modulated RF signal to be fed to the receiver. The AF signal
produced by the demodulator within the receiver, is analyzed to produce results of the test.
Selecting the Rx TEST mode does not disable the functions of the Tx TEST mode. The receiver
circuits remain active at their last settings. The AF generators will also continue operating at their
last settings unless either is enabled as a modulation generator. Calling up one modulation
generator will allow the other to function as an AF generator for Tx testing, but using both as
modulation sources will remove both from Tx test use.
RF oscillator
Refer to the overall block diagram, Fig. 4-2, Simplified block diagram on page 4-5, and the
detailed block diagram of the RF oscillator in Fig. 4-5 on page 4-14.
A signal in the frequency range 576 - 1152 MHz is generated on RF oscillator board C2, passed to
an amplifier and splitter.
One output from the splitter is passed to the RF generator control board C1, where it is divided
down to 2.5 MHz under Fractional N control and fed back to the RF oscillator board C2. This
signal is compared with a 2.5 MHz signal derived from the 10 MHz standard. The error signal is
loop filtered and used to lock the oscillator.
The second RF output from the splitter on the RF oscillator board C2, is fed to the RF divider
board C3. On this board the signal is routed through a series of filters which selects sub-
harmonics of the original signal so as to divide it by factors of 2, 4, or 8.
The frequency range of the RF signal is therefore extended to cover 72 - 1050 MHz
The signal on the output of the RF divider board C3 is routed to bypass board C4. For RF
generator output frequencies above and including 72 MHz, the signal is routed across C4 to the
output amplifier board A6/1.
When a signal generator output within the range 400 kHz to 72 MHz is required, the output signal
from the RF divider board C3 is routed from the bypass board C4 to the beat frequency oscillator
board C5. The frequency range of signal fed to the beat frequency oscillator board C5 is within
the range 320.4 MHz and 391.999999 MHz. A 1280 MHz signal from A9/1 is divided by 4 (to
produce a 320 MHz signal) and mixed with the signal from the bypass board C4. These two
signals are mixed and the resultant signal of 400 kHz to 71.999999 MHz is amplified, then filtered
off, routed back to the bypass board C4, then to the Output Amplifier board A6/1.