Icom IC-H12, Руководство по обслуживанию

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2 TRANSMITTE R CIRCU ITS
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MIC AMP L I F I E R C I R CU I T
Audio signals from the microphone are fed to the limiter amplifier, consisting of 0125 � 0128, which
has 6dB/Octave response between 300Hz and 3KHz.
The output of the limiter amplifier is similar to rectangular waves and includes harmonics.
These harmonics are eliminated by the low-pass filter 0 129, which cuts 3KHz or higher.
Filtered signals are fed to the VCO in the P L L board to make modulation.
3 - 2 - 2 MULT I P L I E R A N D D R I V E R C I RCU I TS
The VCO oscillates a half of a transmitting frequency, thus the multiplier 0208 and 0209, multiplies it
two times to obtain 1 56MHz* transmitting frequency.
This 156MHz* signal is fed to amplifiers 0211 and 0212 through band-pass filter L219, L 220 and L221,
L 222 to obtain 200 milliwatts pure 1 56MHz* signal. While switching from receive to transmit, 021 0 is
turned ON by the charged voltage of C269, until the charged voltage has been discharged, and th is
function cuts the bias voltage of 0211 � 0213.
This prevents transmission of unwanted signals.
(*: This frequency differs depending on the version.)
3 - 2- 3 POW E R AMP L I F I E R C I RCUIT
This output signals from 0212 is fed to the power amplifier 0213, and amplified to 2. 5 watts.
In the transmit mode, D216 and D21 7 are turned ON, and D217 makes L228 have high-impedance and
D216 feeds the signals to the antenna through the low-pass filter.
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PLL C I RCU ITS
3- 3 - 1 LOC A L OSCI L LATO R C I R CU I T
The crystal oscillator 0206 oscillates with X202* for receive, with X 203* for simplex transmit, with
X 204* for duplex transmit
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and the signal at two times this frequency is taken from the collector of
0207, and fed to the mixer of the P L L circuit.
( *: These frequencies differ depending on the version. * *: Some versions are not provided.)
In the receive mode, R+5V is applied to D21 0 through R 223, L211 and R 227, and D210 is turned ON
and selects X 202.
In the simplex transmit mode, T + 5V is applied to D21 1 through R224,_ L 212 and R228, and D21 1 is
turned ON and selects X 203.
In the duplex transmit mode, T+5V is applied to D212 through R225, L 213 and R229, and D212 is
turned ON and selects X 204. (Some versions are not provided.)
3 - 3 - 2 MIXE R, LOW -PASS Fl L TE R AN D AMP L I F I E R C I RCUITS
The output signals from the local oscillator circuit and the VCO signals fed through buffer amplifiers
0202 and 0203 are mixed by the mixer 0204. The output signals are fed to the low-pass filter to filter
out only the signals below 7MHz, then fed to 0205 to be amplified to proper drive level (more than
3Vp-p) of the programmable divider IC201.
3 - 3 - 3 P R OG R AMMAB L E D IV I DE R CI RCU I T
The input signals a t Pin 2 of IC 201 are divided b y the BC D input signals from the matrix board at Pin
3 � 14.
The programmable divider is also called the 1/N counter and the BC D value is N.
The relationship between the operating frequency and the divide number N is:
N (divide number of programmable divider)= ( Receive frequency(MHz) -
Local Oscillator Frequency*)
I
0. 015
*Use 147. 995MHz, 148. 000MHz, 148 . 005MHz or 148 . 01 0MHz, so that the N number becomes an
even number, and adjust the local oscillator frequency for the used frequency. ( R efer the frequency
tables on page 7- 12�1 5).
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