Agc And Smeter; Cwn Filter; Notch Filter - Swann CUBIC ASTRO 102 BX Service Manual

OCUBIC
COMMUNICATIONS
S.,AItI
DIVIBION
Set the RIT control to O. Push the RIT control to turn it on (RIT li-
ght lighted). If the display frequency changes, adjust the RIT CENTER trim-
pot (R536) on the PTO control board so that there is no change in the dis-
play frequency between RIT on and RIT off. Verify that the RIT control
varies the frequency of the display ± SOO to 1500 Hz.
Turn the PTO A control fully counterclockwise and note how much the
display frequency goes below 14000.0 kHz. Now turn the PTO A control to its
clockwise limit and note how much the display frequency goes above 14500.0
kHz. The amount that the frequency extends beyond the lower and upper band
limits should be greater than 50 kHz and within 10 kHz of each other. If
this is not the case, adjust trimmer c606 on PTO A for the proper frequency
range.
Set the PTO MODE switch to PTO Band repeat the above procedures for B.
EXCITER I. F. ADJUSTMENTS
Set the MODE switch to CW, the PTO MODE switch to PTO A, the PASSBAND
control to its 12 o'clock position, and adjust PTO A for a display frequency
of 14300.0 kHz. Conneet the output of the RF generator to the ANTENNA con-
nector on the rear apron of the unit. Set the RF generator output for 50 uV
and adjust its frequency for maximum S meter reading on the unit. Adjust
transformers TlOl, Tl02, Tl03 and TI04 on the exciter board for a maximum S
meter reading.
AGC AND S METER CALIBRATION
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Use the same test setup as previous section. Connect the oscilloscope
probe to the cathode of diode CR123 (AF in line) on the audio board. Adjust
the AGC THRESH trimpot (RlOl) on the audio board for 600 mV p-p indication
on the oscilliscope screen. Disconneet the oscilloscope probe.
Adjust the S METER CAL trimpot (RIIO) on the audio board for an S
9
in-
dication on the unit's meter.
CWN FILTER ADJUSTMENT
Set the MODE switch to CWN and connect the frequency counter across the
units speaker terminals, keeping the rest of the test setup the same as for
the previous section. Adjust PTO A for a 1650 Hz ± 20 Hz speaker audio tone
and adjust CWN trimmer capacitors C130 and C134 on the exciter board for a
maximum S meter reading. Switch the MODE to CW and verify that the S meter
reading changes by less than one S unit.
NOTCH FILTER ADJUSTMENT
Use the same test setup as before. Conneet the AC voltmeter or oscil-
loscope across the speaker terminals. Adjust PTO A for a 1650 ± 20 Hz tone
in the speaker. Adjust the NOTCH FILT control for minimum speaker audio
output, then adjust the NOTCH FILTER ADJUST trimpot (R17S) on the audio bo-
ard for minimum speaker audio output. Repeat the adjustments of NOTCH FILT
and N F ADJ controls until there is no further decrease in the speaker audio
output. The notch filter should attenuate the speaker audio by more than
25 dB. Verify that speaker audio output can also be attenuated
by
the notch
filter with speaker audio tones of 400 Hz and 2500 Hz. Disconneet the freq-
S-lO