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SL7000SERIES HAND HELD
to antenna switch D202 then applied to Antenna Connector.
3) RECEIVER
* ANT SWITCHING CIRCUIT
Signals from antenna connector fed to the antenna switching circuit . In receive mode, D201 is turned off, which
isolates the antenna from the transmitter circuit, so that the incoming signals are fed to the RF amplifier through
L209.
* RF AMPIFIER CIRCUIT
The signal, from the switching circuit, is fed to the RF amplifier Q861 through a band pass filter made up of coil,
varicap diode and capacitor.
* FIRST MIXER CIRCUIT
The amplified signals are fed to Gate 2 of the first mixer Q831 through C851.
First local oscillator signal is supplied to Gate 1 of Q831 from the VCO circuit through C841 to convert the RF
signal into the 46.35MHz first IF signal.
* IF CIRCUIT
The first IF signal from Q831 is fed to the matched pair crystal filter, X821, then the signal is amplified in Q821. This signal
is fed to IC801, which is composed of the second mixer, limiter amplifier, quadrature detector and active filter circuit.
45.9 MHz is produced at the PLL circuit by tripling it's reference frequency 15.3 MHz.
The second local oscillator at
and is fed to the second mixer with the first IF signals to convert into 450kHz second IF signals.
The second IF signals leave through pin 3,and are fed to external ceramic filters X802 then back to IC801 (pin 5)
to be amplified and detected. The detected AF signals are output from pin 9.
* Squelch (mute) CIRCUIT
The squelch circuit switches off the power amplifier when no audio signal is present. The squelch circuit consists of
a 16 kHz band pass filter and a noise detector circuit.
* Speaker Audio Amplifier CIRCUIT
After signal detection and audio filtering, the low level audio is returned to the RF circuit via VR371. This is then
routed to Pin 4 of IC371, (TA7386F), to provide speaker audio. IC371 is enabled by a logic high applied to
Q372which in turn enables Q371, applying power to Pin 2 of IC371.
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