DRM06THHigh : 20W Low: 2W
Modulationvariable reactance frequency modulation
Max deviation+/- 5.0kHz
Spurious-60dB or under below carrier
MicrophoneElectret Condenser Microphone
Operatin ModeSimplex/Semi-Duplex
Offset0 to +/-15.995MHz freely programmable
(DRM03SX)
Receiver
Receiver sysDouble-conversion superheterodyne
I.F.10.7MHz and 455kHz
SensitivityDRM03SX0.16uV (-16dBu) 12dB SINAD
DRM06DX0.25uV (-12dBu) 12dB SINAD
Selectivity+/- 6kHz or under at -6dB
+/- 15kHz or under at -60dB
AF Output2.5W with 8ohm at 10%distortion
8ohm
Page 2
CIRCUIT DESCRTPTION
1) Receiver System
1. Front EndThe signal from the antenna is passed through a low-pass filter and input to
the voltage step up circuit consisting Of L14. The signal from L14 is led to
the gate of Q1. D19 is the diode limiter circuit against the excessive input
power of more than 20dBm. Q1 is the FETwhich has two gates. The
voltage of the gate 2 is set higher to get the high gain and sensitivity. The
signal from Q1 is led to the triple band pass filter (L4, L5, L6), and gets the
high image rejection ratio.
2. Mixer CircuitThe signal from the triple band pass filter is converted into the first IF signal
of 17.2MHz. The receiving signal is led to the gate 1 of Q2, and the first
local oscillator signal is led to the gate 2 of Q2. To get the high conversion
gain, the local oscillator signal voltage is set to about 1V. To reduce the
high adjacent channel interference, the band width of the FL2 is set to
20kHz. The signal from FL2 is amplified by Q8, and input to FM IF system
IC3 of TK10487.
3. IF CircuitThe TK10487 has the second local oscilltor circuit, mixer circuit, detector
circuit, squelch circuit, and so on. Pin1 and 2 are the terminals of the crystal
oscillator circuit. Pin2 (emitter) is connected to the ground via the resister
R3 to prevent the oscillator from decreasing the power at the low temperature. Pin4 of IC3 is connected to FL1 directly because the matching resistor
for ceramic filter is built-in. The quadrature circuit (pin10 of IC3) is connected to the ceramic resonator X2 for the temperature stability and good
quality. The signal from pin11 of IC3 is connected to the LPF. The detected
AF signal, which has flat frequency characteristics, is led to the control unit
and used as both squelch signal and tone squelch signal. De-emphasis
circuit consists of R31, R32, C26 and C27. The LPF amplifier consisting of
Q5 and Q6 is located far away from the VR in the control unit, so it outputs
the high voltage signal to prevent S/N from the deterioration. The squelch
switch circuit consists of Q4 and Q16, and switches on/off at the point where
there is no voltage to prevent from the switching noise. The S meter signal
from pin12 of IC3 is led to the CPU in the control unit after adjusting the level
at D20 and VR5. The S meter signal is thermal compensated by TH1 and
stabilized. The noise amplifier consists of pin13 and 14, the built-in OP
amplifier in IC3. The output signal of noise amplifier is amplified by Q14,
rectified by D5, and then led to the pin15 (hysteresis comparator input) of
IC3.
4. AF CircuitIC4 is about 5W audio power amplifier IC. When the capacity of pin1 in C16
is increased more, the output incidental noise becomes smaller. The highpitched tone becomes smaller at the same time, This radio's capacity of
C16 is determined considering the high-pitched tone.
PAGE-3
2) Transmitter System
1. Modulation Circuit
The microphone amplifier IC1 (IDC, LPF) consists of two operational amplifiers. The signal from the microphone is led to pre-emphasis circuit consisting
of C36 and R47 and then to the limiter circuit. The limiter circuit uses the
saturation of the OP amplifier. The amplified signal is input to the low-pass
filter IC1A. The output signal from the microphone amplifier is passed
through variable resistors VR2 for modulatlon adjustment and input to the
VCO unit. Sub tone deviation is determined by R24, R25 and VR2. The
radio does not have the adjustment variable resistor for sub tone deviation.
2. TX Amp. Circuit
The signal from VCO is ampriied by TX, RX wide band LO amplifier Q19.
The signal from Q19 is passed through the transmission/reception selector,
and amplified byQ20 and Q15. The PA unit is driven at 200mW driving
power.
3. PA Circuit
IC5 is 20W(M06DX) powered amplifier module. The output power is controlled by
the voltage of V1. The RF signal amplified 20W in PA is passed through D3
and three-stage transmission/reception low-pass filter, and input to the
antenna connector.
4. ALC Circuit(M06DX)
The power detection circuit consisting of D17 and D18 rectifies the output
signal voltage. The detected DC voltage is led to the VR1 (power adjust
trimmer), and amplified by Q3, Q9 and Q13. Output power is controlled by
voltage of V1 in IC5 and collector voltage of Q15. When the temperature
goes up unusually, the power down circuit consisting of R101 and TH2
works to prevent the device from the destruction.
3)PLL Circuit
(M06DX)
The VCO unit is designed for the PLL circuit, putting the VCO on one side,
and PLL circuit on the other side.
Q301 in the VCO is grounded using the gate oscmator, and its frequency
covers 50MHz to 54MHz without transmission/reception shift circuit.
IC301 is pulse swallow system based PLL IC with the built-in prescaler,
which synthesizes 150MHz-band signal.
The loop filter consisting of Q302 and Q303 is the active type.