Icom IC-R7100 Service Manual page 10

Pin 7 ol lC2b supplies a tuned voltage to BPF4. Q9 and
010. switch Ihe gain and ortset vollage ol IC2b ON or OFF
and convert the varlalions of 2 PLL loek voltages lnto a
continuous tuned voltage.
Tabla 2 shows Ihe retat lon between receive frequency
and 1st IF Irequency.
Pin 1 ol IC3b supplies a luned vollage to Ihe luned neten
clrcuil on Ihe TRAP UNIT.
011 swilches Ihe offset voltage ol IC3b ON or OFF and
converts the variations of 2 Pll loek voltages into a
continuous luned voltage.
RECEIVE FREOUENCY [MHz] 1et IF FREOUENCY [MHz]
25- 89.9999
778.7 (FI1)
90- 249.9999 778.7 (Fll)
250- 511 .9999
778.7 (FI1)
512-1024.9999 266.7 (FI2)
Tabl.2
Fig. 4 shows the characteristies of the 1st IF filter.
3·1·6 1st MIXER CIRCUIT (MIX1 UNIT)
'lST IF FILTER CHARACTERISTICS
I
I
I
I
I
I
I
I
I
I
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Frequency
Fig. 4
I, -21.4
MHz
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The 1st mixer circuit converts Ihe received signailo a
IIxed Irequency ol the 1st IF signal wilh a PLL output
frequency. By changing the PLL frequency, only the
desired Irequency will pass Ihrough the FIL1 UNIT or
FIL2 UNIT al the next stage of Ihe 1st mixer.
A 778.7-1291 .7 MHz (0 dBm) lst LO signal is appl ied
la a bandpass 111Ier (strlp line. L78. Cl34. C59. C77. C53-
C55) on
tne
MIXl UNIT to suppress unwanted signals
Ihrough Pl from Ihe PLL UNIT. The filtered slgnal is
amplified at Ihe 1st LO amplifiers (05. 06). The 1 st LO
amplifiers (05, 06) employ wide frequency band amplifiers
wlth approximalely 10 dB gain and amplify the 1 st LO
signaI la approxlmalely 10 dBm.
The 25.0000-1024.9999 MHz slgnals are mixed al ICS
with Ihe 1st LO signal la produce a 266.7 or 778.7 MHz
1st IF signal. ICS employs a DBM (Double Balanced
Mixer).
Tabla 1 shows Ihe relation between receive frequency and
1sI LO frequency.
(1) FIL1 CIRCUIT (25-511.9999 MHz)
The 778.7 MHz 1
st
IF signal is applied to an inductlve \
bandpass
lilter (Fll) to suppress out-of-band signais. Fll
sets Ihe center frequency at 778.7 MHz and covers a
5 MHz bandwldlh. The fillered signal is applied to a noten
filter (L51. C79) la suppress Ihe image interference signal
(757.3 MHz).
RECEIVE FREOUENCY [MHz]
1st lO FREOUENCY [MHz]
25-
89.9999
803.7-
868.6999
90- 249.9999 868.7-1028.6999
250- 511 .9999 1028 .7- 1290.6999
512-1024.9999 778.7-1291.6999
roble
1
3·1·7 1st IF CIRCUIT
(RF, FIL1 AND FIL2 UNITS)
(2) FIL2 CIRCUIT (512-1024.9999 MHz)
The 266.7 MHz 1st IF slgnal Is applied la a helical
lilter (L46. L47) to suppress out-of-band signals Ihrough
a series resonant circuit (L73. C66). The helical filler
sets the center frequency at 266.7 MHz and covers a
5 MHz bandwldlh. The filtered slgnal passes Ihrough a
nolch fliler (L67. L68. CS8) la suppress Ihe image inler·
ference slgnal (245.3 MHz) and is then applied to series
resonant clrcults (L74. C90). The series resonant circuits
atlenuate out-ot-band signais.
The 1st IF signal (226.7 or 778.7 MHz) Is applied to a
1 st IF amplilier (08) providing approxlmalely 10 dB gain
over a w ideband frequency range. The 1st IF amplifier
employs
a feedback circuit (L43.
C72. R56) la oblain
stabie gain in Ihe wlde Irequency range. The 2nd IF
slgnal is applied 10
t\Yo
separate filters depending on Ihe
receive frequency.
The 266.7 or 778.7 MHz 1st IF signal Is applied la a low-
pass filter (strip line. C139-C141) la suppress tne high
harmonie components on the RF UNIT.
3-4