Icom IC-R7100 Service Manual page 9

(3) BPF3 (250.0000-511.9999 MHz)
The 250.0000 -511.9999 MHz signals pass through a
high-pass filt er (L32, L69, C34, C35. C51, C133) to sup-
press th e interference signaIs in low frequencies. The
filt er cuts out the 240 MHz frequenc ies. The filtered
signals are applied to an RF amplifier (a3) via a tuned
bandpass filter (D2 1. D22, L33. L34). The amplified
signaIs are applied to a 2nd RF amplifier (07) through
another tun ed bandpa ss filt er (D23, D24, L36, L37).
D21 ---D24 employ varactor diodes whi ch are controlled
by the PLL J oek vo ltage. The voltaçe is current-ampl ified
at the DC amplifier circuit (IC3 a. IC2a) and is then
appüed 1 0 Ihe varacto r diodes. These varac tor diodes
tune Ihe c enter frequency of an RF passband tor wide
bandwidth receiving and goed image response rej ection.
(4) BPF4 (512.0000 -1024.9999 MHz)
RF relays are used instead of a diode switching system
tor signals above 512 MHz. To drive these relays, Q14
and 015 are used as current amplifiers.
The 512.0000-1024.9999 MHz signals pass through a
parallel resonant ci rc uit (D26, L39, C45) to suppress half
o f Ihe recei ve frequency interferen ce signaIs and are
then applied to an RF circuit
(0 4)
via a tuned bandpass
filter. The amplified signaIs are applied to a 2nd RF
amplifier (07) through a tuned bandpass fil ter. The tuned
bandpass filters consist of a strip line and 0 27-030 and
ensure stabie ope ration at high fr equenci es.
The voltage is current-amplified at the
De
amplifier circuit
(/C3a. IC3b) and is th en applied to the varactor diodes.
These varactor diodes tune the center frequency of an RF
passband tor wide bandwidth receiving and goed image
response rejection.
The signaIs from the tuned notch circuit are appli ed to a
low-pass fiiter (strip line, C78, C82, C85. C89, CI 3?) to
suppress high harmonie components of the 1st LO signa!.
The filtered signals are applied to a 1st mixer circuit.
3·1·5 TUNED CONTROL CIRCUIT (RF UNIT)
The tuned contr ol circuit c onverts the PLL loek voltage to
tuned voltage tor the BPFI - BPF4 on the RF UNIT and
the tuned notch circ uit on the TRAP UNIT.
Fig. 3 shows the relation between the PLL loek voltage
and each tuned voltage. in the BPF1 -BPF4 on the RF
UNIT and tuned notch circuit on the TRAP UNIT.
• PLL LOeK VOLTAGE AND TUNED VOLTAGE
D27-030 employ va raetor diodes which are contro lled
by the PLL loek voltage. The voltage is eurrent-amplified
at
tne
DC amplifier ci rcuit (IC3a, IC2b) and is then applied
to the varactor diodes. These varactor diodes tune the
c enter frequeney of an RF passband for wide bandwidth
reeeiving and good image response rejection.
(5) 2nd RF AMPLIFIER
The 2nd RF amplifie r (0 7) employs a wide frequency
band amplifier with approximately 10 dB gain.
The 25 .0000-1024.9999 MHz signaIs from tour separate
filters are applied to the 2nd RF amplifier (07). The 2nd
RF amplifier has a feedback circuit (L42, C67, R47) to
obtain stable gain in the wide frequen cy range. The
amplified signa Is are then applied
10
a tuned notch circuit.
3·1·4 TUNED NOTCH CIRCUIT (TRAP UNIn
The luned notch circuil prevents the 1st Lü signal from
enlering the antenna connector.
This circuit consists of a strip !ine and 031 -034. The
noten frequency is adjusted to mateh the 1st Lü frequency
by a control voltage coming from IC3b (pin 1).
D31--D34 employ varaeter diodes which are eontrolled
by the PLL loc k voltage.
The PLL lock voltage (CV) passes through the DC amplifier
(IC3a) to convert the impedance and Is then applied to
the operational amplifiers (ICl a, ICI b, IC2a, IC2b, IC3b).
Pin 1 of ICI a supplies a tuned voltage to BPF1 . R68
and R66 control the gain and offset voltage of ICl a
respeetively.
Pin 7 of IC1b supplles a tuned voitage to BPF2. D53
and R157 adjust the gain voltage of tCI b to fit the
c haracteristl cs of BPF2.
Pin 1 of IC2a supplies a tuned voltage to BPF3.
•
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