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SECTION 4.
4-1 RECEIVER CIRCUITS
RF CIRCUITS
The RX signal from the antenna is passed through the LPF
and antenna SW, then filtered by the 2-staged tuned BPF
to eliminate unwanted out-of-band signal. The filtered RX
signal is amplified by the RF AMP, and filtered by another
2-staged tuned BPF to obtain a good image response, then
applied to the 1st IF circuits.
The tuned BPFs are tuned to the RX frequency by applying
adequate tuning voltages; "T1" and "T2" to the variable
capacitors.
• RF CIRCUITS
From the TX circuits
D28
Q22
To the 1st IF circuits
RF
BPF
AMP
T2
1ST IF CIRCUITS
The RX signal from the RF circuits is applied to the 1st IF
mixer and mixed with the 1st LO signal from the RX VCO,
resulting in the 46.35 MHz 1st IF signal. The 1st IF signal is
filtered by the crystal filter, amplified by the 1st IF AMP, then
applied to the 2nd IF circuits.
• 1ST IF CIRCUITS
Q10
RX VCO
BUFF
Q24
To the 2nd IF&demodulator circuits
IF
AMP
CIRCUIT DESCRIPTION
ANT
D3,D22
ANT
LPF
SW
D24,D26
BPF
T1
D5,D6
Q8
LO
To the TX circuits
BUFF
SW
LPF
FI1
Q23
46.35MHz
From the RF circuits
XTAL
BPF
1st IF mixer
2ND IF CIRCUITS AND DEMODULATOR
The signal from the 1st IF circuits is applied to the IF
demodulator IC which contains the 2nd IF mixer, 2nd IF
AMP, FM detector, etc. in its package.
The 1st IF signal is applied to the 2nd IF mixer and mixed
with the 2nd LO signal resulting in the 450 kHz 2nd IF
signal.
The 2nd LO signal is generated by tripling the 15.3 MHz
reference frequency signal oscillated by the reference
frequency oscillator (TCXO).
The converted 2nd IF signal is filtered by the crystal filter/
filters to eliminate unwanted signal, and amplified by the
2nd IF AMP, then demodulated by the detector circuit which
employs a discriminator as the phase shifter.
The demodulated AF signal is applied to the RX AF circuits.
• 2ND IF CIRCUITS
X2
15.3MHz
TCXO
Q26
IC2
PLL
X3
MB15A02
IC
45.9MHz
BPF
D/A
D31,D32
converter
W/N
SW
SQIN
450kHz
DISC
CERAMIC
BPF
IC57
R2A20178
To the RX AF circuits
4 - 1
IF IC
I C3:NJM2591
FI2
450kHz
CERAMIC
BPF
X1
FI3
Discriminator
W/N
Q27,
SW
D33,D34
NOIS
NWC
From the 1st IF
circuits
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Do you have a question about the IC-F4001 and is the answer not in the manual?
Questions and answers
ptt pressed but not tx
The Icom IC-F4001 may not be transmitting when the PTT is pressed due to several possible reasons:
1. Transmit Inhibit Function – Transmission is restricted if:
- The channel is muted (PMR operation only).
- The channel is busy.
- A signal with an unmatched (or matched) CTCSS or DTCS tone is received.
- The selected channel is a "receive only" channel.
2. Time-Out Timer – If the transceiver has been transmitting continuously beyond the pre-programmed time limit, the time-out timer activates and stops further transmission.
3. Penalty Timer – After the time-out timer activates, the penalty timer may further inhibit transmission for a set period.
4. Power Supply Issues – If the transceiver is connected to a power supply with incorrect voltage or reversed polarity, it may not function properly.
5. Antenna Damage – If an RF signal stronger than 20 dBm (100 mW) was applied to the antenna connector, the transceiver’s front-end could be damaged, affecting transmission.
Checking these factors can help identify and resolve the issue.
This answer is automatically generated
Q73 trasistor does not work when PTT pressed but software is ok