Table of Contents
Advertisement
8. ADJUSTMENTS
8.1
FM TUNER
e Connect the FM
SG (FM signal generator) to
the
FM
ANTENNA
30002
terminals
via a 3000
dummy antenna.
e Switch
the
FUNCTION
selector
to the FM
position,
the
FM
MUTING
switch
to the OFF
position.
e The tuning coils in the FM front end dose not
have
an
adjusting
core.
Consequently,
tracking
adjustments at 90OMHz are performed by regulating
the gap between
rotor and stator
of the tuning
capacitors (VC1, VC3
and VCs).
The expression
"adjust VC (VC:i, VC3, VCs) found in the text
means
that the two outer rotor blades of each of
these
tuning capacitors are to be extended
out-
wards with spatula (Part No. GGK-066) as shown
in Fig. 8-1.
Stator
Rotor blade
| l
Stator
Rotor blade
~
Pd
A
Spatula
> fL a
(GGK-066)
Fig. 8-1 Adjustment of tuning capacitor
1.
Set the TX-6800
dial point to a frequency in
'
the 106MHz
region so that there will be no
input signal.
8.
Next tune more accurately to 1O6MHz, and set
the FM
SG output to 106MHz, 60 to 80dB
(modulation—400Hz, +75kHz deviation).
4.
Adjust TCs
to obtain maximum
deflection of
the SIGNAL meter indicator, and a dead center
reading in the TUNING meter.
10
5.
Then tune the dial pointer to 90MHz, and set
the FM SG output frequency to 90MHz.
6.
Adjust the VCs
to obtain maximum deflection
in the SIGNAL meter, and a dead center read-
ing in the TUNING meter.
7.
Repeat steps 3 to 6 above.
8.
Reset the FM
SG
output level to 20—30dB,
and
adjust
TC:
and
TCs
at 106MHz,
'and
VC:
and VCs
at 90MHz
in the same manner
as described
above in steps 3 to 7. These ad-
justments
will ensure
optimum
sensitivity in
the 90 to 106MHz
range, and minimum
dif-
ference in sensitivity between the two extreme
frequencies.
9.
Retum to a position with no input signal.
10. Rotate
the
N
core
of T2
again
to set the
TUNING meter indicator to dead center.
11. Set the FM
SG output to 98MHz
and 66dB
(modulation—400Hz,
+75kHz
deviation),
and
tune the TX-6800 to this position.
12. Then
rotate
the D core of Tz to reduce dis-
tortion in the demodulator
output (OUTPUT
terminal) to a minimum.
18. Repeat steps 9 to 12 above until both specifi-
cations (center TUNING
meter reading in the
absence
of
input
signal,
and
minimum
dis-
tortion in demodulator output) are satisfacto-
rily met.
Multiplex Decoder
e Connect the MPX SG (FM multiplex generator)
to the FM SG external modulator terminal.
e Set the FM MUTING switch to the ON position.
14. Set the FM
SG
output to 98MHz
and 66dB
(unmodulated),
and tune the TX-6800 to this
position.
15. Adjust VR:
to obtain a 76kHz signal at TP .
terminal,
16. Then set the FM SG output level to 86dB, and
the modulation
mode
to external.
Then with
the
MPX
SG,
set
Main
to
1kHz,
L+R
to
+67.5kHz
deviation,
and
pilot
signal
to
+7.5kHz deviation.
17. Rotate the T: core around by up to 90° in
either
direction
to reduce
the
demodulator
output
(OUTPUT
terminal)
distortion
to a
minimum,
Advertisement
Table of Contents
