Yaesu FT-757GX Technical Supplement page 21

RF
Unit: Receiver Circuits
A. 3rd Local Buffer
Connect the RF voltmeter to the emitter of 01028
and adjust T 101 9 for maximum RF voltage (0. 7 to
0.9 Vrms).
B. 2nd Local Buff er
Connect the RF voltmeter to the jumper between
T1006 and T102 3 on the component side of the
board, and adjust T1022 for maximum RF voltage
(0.25 to 0.35 Vrms).
C. Width Oscillator (Coarse)
1. Connect the frequency counter through a
0.01 uF capacitor to pin 1 of 01022 . Set the
WIDTH control to the 12 o'clock position,
and adjust L1044 for 8.670 MHz ±100 Hz on
the counter (coarse adjustment).
2. Connect the RF voltmeter to gate two of
01016 and adjust T1019 for maximum RF
voltage (0.5 to 0.6 Vrms).
D. RX IF Transformers
Preset VR1001 fully clockwise and adjust VR1010
to the point where the S-meter just begins to
deflect. Apply a 60 dB signal at 14.000 MHz from
the RF signal generator to the antenna jack, and
adjust T1016 through T1010 and T1007 through
T 1004, in that order, for maximum S-meter deflec­
tion. Reduce the signal generator level as necessary
to keep the meter below full scale.
E.
Width Oscillator (Fine)
With the WIDTH and SHIFT controls both set to
the 12 o'clock position, switch the mode back and
forth between LSB and USB, adjusting L1044 for
the same noise pitch.
F. IF
Gain and S-Meter Sensitivity
1. Apply a 6 dB signal at 14.000 MHz from the
RF signal generator to the antenna jack, and
adjust VR 1001 for an S-meter deflection of
S-1.
2. Increase the RF signal level to 100 dB and
adjust VR1011 so that the S-meter indicates
just to full scale.
G. Noise Blanker
Connect the DC voltmeter to gate two of 0 101 3 ,
and with the RF signal generator connected as
above, set the RF level to 40 to 60 dB at 14.000
MHz. With the NB button depressed, adjust T 100 8
and T 100 9 for minimum DC voltage on the meter.
H. FM 3rd Local
With the RF signal generator connected to the
antenna jack, apply a 40 to 60 dB signal at 14.000
MHz, modulated with a 1 kHz tone at ±3.5 kHz
deviation. Connect the AF voltmeter across the
speaker terminals; set the SOL control fully
counterclockwise, and adjust T 101 7 for maximum
AF voltage on the meter.
I. Squelch Threshold
Beginning with the transceiver in the AM mode,
with no signal applied at the antenna jack, advance
the SO L control gradually from the fully counter­
clockwise position just to the point where the
squelch closes. Then switch to the FM mode, and
adjust VR100 3 to the point where the squelch
again just closes.
J.
FM RX AF Output Level
1. With the AF voltmeter connected across the
speaker terminals, apply a 40 dB signal at
14.000 MHz (with no modulation) from the
RF generator to the antenna jack. Set the
transceiver to the USB mode, tune for a
heterodyne, and adjust the AF gain control
for 0.1 V on the AF voltmeter.
2. Switch to the FM mode and modulate the RF
signal with 1 kHz at ±3.5 kHz deviation, with­
out changing the generator output level.
Adjust VR1002 for 0.1 V on the AF voltmeter.
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