Carrier Null Adjustment - Heathkit SB-401 Assembly Manual

( ) Return the FUNCTION switch to STBY.
NOTE: The preceding five adjustments can be checked after
the Transmitter is in the cabinet by using a recei vcr set to the
operating frequency and observing the "S" meter for
minimum readings as the adjustments are made.
NOTE:
The object
of
the
following
CARRIER NULL
adjustments is to reduce the carrier output as much as
possible. If the following adjustments will not reduce the
VTVM
reading to approximately
"0",
perform the balanced
modulator transformer adjustment again (to eliminate
possible interaction).
( ) Repeat the previous two steps until the same VTVl\'l
reading is obtained in the USB
and
LSB positions of
the MODE switch. ( ) Place the ~10DE switch in the USB position.
( ) Rotate the LEVEL control fully counterclockwise,
(
) Place the MODE switch in the LSB position and adjust
the CARRIER NULL capacitor to the same VTVl\l
reading obtained in the previous step.
( ) Key the Transmi tter arid adjust the DRIVER control
for a maximllm indication on the VTVM.
( ) Place the lVI0DE switch
ill
the USB position and adjust
the CARRIER NULI.J control for a rnillilTIltm
indication on the VTVM.
( ) Place the BAND switches in the
3.5
position.
( ) Place the l\IODE switch in the LSB position and adjust
the
CARRIER NUI...
I.I
capacitor to the
same VTVl\l
reading obtained
ill
the USB position.
NOTE:
Leave the VTVM
RF probe
connected to the hare
wirebetween pins 5 of VI 0 and VII.
CARRIER NULL ADJUSTMENT
( ) Replace the 15.895 i\1Hz crystal.
( )
Short lug 2 of the l\lIC connector
t()
tile chassis with a
jumper
wire, or connect a microphone and pres~ the
push-to-talk button; then alternately adjust the
CARRIER NULL control and capacit()r for a rilillirnlirn
indication on the VTVM.
( ) Disconnect the VTVl\I.
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