530 Chapter11
Synthesizer Section
Confirming a Faulty Synthesizer Section
10.Set the spectrum analyzer to the following settings:
Center frequency ........................................................ 300MHz
Span ............................................................................ 100MHz
11.If the 1st LO is present, a signal should be displayed at about
−10 dBm (approximately ±20 MHz from the center frequency). If no
signal is displayed and ERR 338 LOMA AGC, ERR 339 SBTX AGC, or
ERR 340 SAMP AGC is not present, suspect the A7 LOMA. If no signal
is displayed and ERR 338 LOMA AGC, ERR 339 SBTX AGC,orERR 340
SAMP AGC is present, check the A11 YTO as follows:
a. Set jumper A14J23 to the TEST position.
b. Set the spectrum analyzer to the following settings:
Center frequency ......................................................50Hz
CF step ................................................................ 300MHz
Span .............................................................................0Hz
c. Connect a power meter directly to the output of the A11 YTO.
d. Press the spectrum analyzer step-up key and measure the YTO
output power at each step.
e. Make sure that the A11 YTO output power is between +9 and
+13 dBm.
f. Set jumper A14J23 to the NORM position and reconnect the A11
YTO.
Check A14
frequency
controlassembly
(steps 12-18)
12.On the spectrum analyzer press
PRESET, SPAN, ZERO
SPAN, CAL, MORE 1 OF 2, FREQ DIAGNOSE, and FRAC N FREQ. Note
the fractional N oscillator frequency. (Ignore the minus sign, if
present.)
13.Check A14J304 (FRAC N TEST) port with a spectrum analyzer for
this exact frequency. The amplitude should be approximately
-10 dBm.
14.Disconnect W32 from A14J501 and connect the output of a signal
source to A14J501. Remove the jumper from A14J23. Connect the
positive lead of a DVM to A14J23 pin 1, and the negative lead to
A14J23 pin 3. See Figure 11-3 on page 531.
15.Set the signal source to the following settings:
Power ........................................................................... 0dBm
Frequency.............................. Frequencyrecorded instep12
16.Tune the source 1 kHz below the fractional N frequency. The voltage
measured on the DVM should be approximately 12 Vdc.
Fractional N Oscillator Frequency = _________________MHz
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