Models 78100A. 78101A Section V
Maintenance
a. Disconnect the 10020A Probe from the Spectrum 5-64. Capacitors ZlCl and C2, and Z2C1 and C2 are
Analyzer RF Plug-in and connect it to the 8901A Modula- located at the ends of RF resonators Z1 and 22, which are
tion Analyzer. transmission lines fabricated as part of the HF board. They
are adjusted in two stages:
b. Disconnect the AFC wire attached to AFC pin on HF
board. 1. The image frequency is rejected by adjusting Z1C2 and
Z2C2 to resonate in series at the image frequency. The
c. Adjust C30 (Figure 5-9) to bring L.O. frequency to impedance at series resonance is very low and bypasses or
within +lo0 Hz of that specified in Table 5-6. shunts the incoming image frequency to ground.
2. The resonators are then tuned for parallel resonance at
d. Reconnect AFC wire (9-1-3) to AFC Pin and remove the carrier frequency (by Z1C 1 and Z2C l), which provides
bottom cover of receiver allowing access to the LF board.
the required passband and RF amplification.
e. Remove power from receiver and connect TPl on LF
board to ground with a clip lead. (See Figure 5-7 for loca- An interstage adjustment with C8 tunes the collector of Q1
for a pass band at the carrier frequency.
tion of TP l .)
f. Disconnect subcarrier wire (9-7) from ?SUB? pin on a. Disconnect P2 of the HF Board (Figure 5-9) from
HF board (see Figure 5-16). chassis cover P1. Connect P2 to the remote antenna connec-
tor, 53, on inside of receiver rear panel (see Figure 5-16).
g. Adjust LF Board R93 (Figure 5-7) to obtain a L.O.
frequency that is greater than 5 kHz but less than 10 kHz b. Set 8656A frequency for the Carrier Frequency of the
below that frequency specified in Table 5-6. Adjustment channel under test (Table 5-6). Adjust amplitude for
closer to 5 kHz better protects against crosstalk. -40 dBm.
c. Use Cable B to connect the 8656A Signal Generator to
h. Disconnect LF board TPI from ground and connect to the receiver rear panel input BNC antenna connector as
LF board terminal E with a clip lead.
shown in test setup in Figure 5-16.
i. The L.O. frequency should be greater than 7 kHz but
d. Connect 10020A Probe with 250 ohm tip (C- Figure
less than 10 kHz above that frequency specified in Table 5-16) between the Spectrum Analyzer RF input and TP4
5-6. Adjustment closer to 5 kHz better protects against
crosstalk. on HF board. Attach probe ground to RF ground pin on
HF board.
j. Disconnect subcarrier wire from terminal E (+12V
e. Remove power cord from receiver and then remove the
supply) and reconnect it to pin SUB. protective covers from input resonator capacitors ZlCl,
ZlC2, Z2C1 and Z2C2. Now adjust the tuning slugs on
k. Remove 10020A Probe (Cable A, Figure 5-16) from
the HF board. these capacitors CCW until the top of the screw is flush
with the threaded shoulder.
5-62. RF Amplifier Gain and Tuning. f. Reinstall power cord and apply power to receiver.
5-63. The radio-frequency (RF) amplifier filters the input g. Turn ZEROlPER DIVISION/O-1250 MHz Switch on
from the antenna to reject spurious signals before they can 8554L to ?Per Division? position.
reach the mixer stage, to prevent their being converted into
spurious intermediate frequencies (IF). The spurious signal h. With the 8554L Frequency tuned to 22 MHz on the
primarily rejected is the image frequency. It is found at the dial, observe minus 21.82 MHz, 0 Hz and +21.82 MHz on
same frequency separation (21.82 MHz) below the L.O. the spectrum analyzer (Figure 5-18). The +21.82 MHz (IF
frequency that the carrier is found above the L.O. fre- Signal) should be centered on the display.
quency, and thus would produce an invalid signal at the
proper IF if it were mixed with the L.O. output. The RF i. Tune the 8554L to 21.82 MHz with a BANDWIDTH of
amplifier adjustments also maximize the gain at the carrier 300 kHz and SCAN WIDTH of 1 MHz/Division.
frequency to insure satisfactory transmission range and
signal quality. Note: Maintain 8656A output amplitude low enough to
078 100-2 5-25 |
ACEC
HEWLETT-PACKARD
