frequency accuracy. Set the modem in the CW mode
(3) Remove the screws retaining the on-line
and tune the upconverter to 8100 MHz.
modem front panel to the rack and pull the modem
(2) Tune the PA to be used to 8100 MHz. Set
forward a few inches on its slides.
the waveguide transfer switch to route the output of this
(4) Put the modem in the CW mode by turning
PA to the dummy load.
the MODE switch to OPERATE and setting the SOURCE
(3) Leave the other PA (the on-line unit
switch (at upper left behind the front panel) to the ICF
connected to the antenna) either off or in the standby
(5) The 70 MHz IF output signal from the
(4) At the RF test patch panel, patch the test
modem is accessed at its appearance on the IF patch
out jack for the off-line PA to the test translator input
panel. Using the push-on to BNC adapter cable, SMA-
937240, patch from the appropriate modem output
(5) Turn on the test translator.
appearance to the BNC spectrum analyzer jack at the
(6) Check that the test loop cable, W10, and
right end of the IF patch panel. This jack is wired directly
the receiver input cable, W1, are installed as shown in
to J10 at the top of rack 6. Connect a 50-ohm test cable
from J10 (BNC) to the RF input of the HP5253B
(7) Install the HP-5253B plug-in module in the
hetrodyne converter in the frequency counter. Use a
frequency counter and turn on counter.
BNC socket to N plug adapter at the converter.
(6) Measure the modem IF output frequency.
downconverter to be tested to the input of the HP-5253B
The test limits are 70 MHz + 1 kHz. If the tests limits are
plug-in module. Use a BNC to BNC test cable and a
exceeded, refer to the modem maintenance manual, TM
BNC to N adapter for this connection.
c. SHF Transmit Frequency. The upconverter
(9) Tune the downconverter to 7375 MHz.
(10) Operate the off line PA and set its power
output frequency may be checked as follows: CAUTION
output level to 1000 watts.
Do not connect the upconverter output to the frequency
(11) With the frequency counter, measure the
counter without an intervening 10 dB pad. The + 21 dBm
downconverter IF output frequency.
output level of the upconverter may damage the input
(12) If the measured frequency is out of
circuits of the plug-in module in the frequency counter.
tolerance, check the test translator for phase lock.
(1) Be sure that the PA is in the standby
Check the downconverter synthesizer for faults or an out
of lock condition.
Refer to TM 11-5895-1092-34
(2) Set the desired modem in the CW mode
for synthesizer maintenance.
as in b(4) above.
(3) At the IF patch panel, patch the modem to
the desired upconverter. Tune the upconverter to 8100
(4) Insert the HP-5255A plug-in module into
(5) Connect a 10 dB pad to the upconverter
This procedure requires that
output on the transmit patch panel. Connect the SMC-
transmit flex waveguide (W3)
937321 low-loss test cable from the pad to the input of
disconnected from the antenna
the HP-5255A plug-in unit.
Test limits: 8100 MHz 11 kHz
STANDBY before disconnecting
(7) If the measured frequency is out of
tolerance, check upconverter synthesizer for faults or an
out of lock condition. Refer to TM 11-5895-1092-34 for
equipment required to perform this test. Note on figure
8-4 the quantity required for item
d. Down Converter Frequency.
(1) At the IF patch panel, select a modem and
an upconverter which have been previously tested for