Circuit Description; Receiver Circuits - Icom IC-R7000 Service Manual

SECTION 4 CIRCUIT DESCRIPTION
4-1 RECEIVER CIRCUITS
4·1-1 CONVERTER CIRCUIT (MAIN UNIT)
Input signals from the ANTENNA CONNECTOR are
switched by RF relays RL3 and RL4 on the MAIN UNIT
either to through or to the converter circuit according
to receive frequency.
When the receive frequency is 1025-1999.9999MHz,
receive signals are applied to the converter circuit
for heterodyning. This circuit converts 1025-
1999.9999MHz receive signals to 25-999.9999MHz.
A HPF consisting of L9 and CB7-CB9 attenuates
strong interfering signals in the 200MHz band.
When the receive frequency is higher than 1025MHz,
signals from the ANTENNA CONNECTOR are applied
to the HPF UNIT. This unit consists of a HPF and
an RF amplifier. The HPF consists of a strip line, c1-
C6, CB and C10-C16. The HPF attenuates signals
with frequencies below 1200MHz and prevents LO
signals (1 GHz) from leaking through the ANTENNA
CONNECTOR. 01 is an RF amplifier and has a gain
of approximately 10dB at 1200MHz.
X1 and 014 oscillate a frequency of 55.555MHz.
Output from 014 is multiplied by three at L3-L5, C31,
C44 and C46 to form a frequency of 166.66MHz. The
166.66MHz frequency is amplified by 015. Output
from 015 is multiplied by three at 016 to form a
frequency of 500MHz, and then the 500MHz signal
(OdBm) is applied to the MAIN DOUBLER UNIT.
In the MAIN DOUBLER UNIT, output from 016 on the
MAIN UNIT is multiplied by two at 01 to form a LO
signal (1000MHz, 10dBm) tor the double balanced
mixer IC9.
4·1·2 20dB ATTENUATOR CIRCUIT (RF UNIT)
Receive signals from the MAIN UNIT are applied to a
BPF consisting of a strip line, L3 and C1
~cs.
This
circuit attenuates signals that exit the passband of
the BPF.
IC5 switches receive signals through or to the
attenuator.
The attenuator consisting of
R2~RB
provides attenua-
tion of approximately 20dB.
4·1·3 RF AMPLIFIER CIRCUIT (RF UNIT)
Receive signals are switched by diodes D5, D11, D12,
D1B, D19 and D25 to each RF amplifier. With fre·
quencies higher than 512 MHz, RF relays RL 1 and
RL2 are used for the switching.
Receive signals of 25-999.9999 or 1025-1999.9999
MHz are quadrisected as indicated in Table 1, and
then each signal is applied to the RF amplifiers.
Each tuned amplifier has approximately 10dB gain.
Table 1 shows the relation among receive frequencies
(FRx) and RF amplifiers.
RECEIVE FREQUENCY
RF AMPLIFIER
FRx[MHz]
25- B9.9999
BPF1 (01)
1025-10B9.9999
90- 249.9999
BPF2 (02)
1090-1249.9999
250- 519.9999
BPF3 (03)
1250-1519.9999
512~ 999.9999
BPF4 (04)
1512-1999.9999
Table 1
(a) BPF1
Receive signals via D5 are fed to parallel resonance
circuit D6, L 11 and C15 to attenuate interference
signals which frequencies are half of receive fre-
quencies.
Receive signals via D6, L11 and C15 are then applied
to the RF amplifier. The input tuning circuit of the
RF amplifier is composed of varicaps D7, DB and
L 12-L 14. The output tuning circuit is composed of
varicaps D9, D10 and L16-L1B.
These circuits are tuned by the tuning voltage from
IC1(A). In addition, D50 prevents varicaps from being
charged over their maximum rated voltage.
(b) BPF2
Receive signals via D12 are fed to a parallel resonance
circuit consisting of D13, L22 and C25. The circuit
attenuates the interference signals which frequen·
cies are half of receive frequencies.
A series-paralled resonance circuit is composed of
varicap D14, L70 and C61. The circuit attenuates
strong signals of FM and TV broadcasts in a fre-
quency range of B0-110 MHz.
The input tuning circuit of the RF amplifier is com-
posed of 04, varicap D15, L23~L25 and C119. The
output tuning circuit is composed of D17, L27-
L29 and C120.
These tuning circuits are tuned by the tuning voltage
from IC1(B). In addition, D51 protects varicap from
being negatively charged.
4-1