Four State QRP Group Cyclone 40, Инструкция по эксплуатации

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Q4.
The transmit power amplifier utilizes power amplifier transistors Q3 and Q4 in
push-pull Class-E mode to generate 4W nominally from 12v, at 85% efficiency.
When the transmitter is keyed, transistor Q7 is driven on, applying DC power to
the PA drain choke L4, allowing Q3 and Q4 to make power.
When in the receive mode, the PTO output is fed to U2, pins 15 and 17,
buffering and amplifying the sine-wave oscillator signal to create a logic-level
square wave signal. The output of U2-5 is fed to U2-13 to create a logically-
inverted signal at U2-7. The signals at U2-3 and -7, respectively, comprise a
complimentary, push-pull signal at the PTO frequency, driving the gates of PA
transistors Q3 and Q4. The received signal is switched by these transistors,
converting the 7 MHz received signals to 11 MHz for the IF filter.
The IF filter, comprised of X1-X4, is a four-pole, 11 MHz crystal filter with a
Gaussian shape, filtering the CW signal with minimal ringing. The filter is fed
directly from the center tap of the PA output transformer, consequently, no
transmit/receive switching of the antenna is required.
The output of the IF filter is amplified by Q5, and fed to the active mixer circuit of
Q1 and Q2. The 11 MHz LO signal is fed into the emitters of Q1 and Q2, mixing
against the IF signal, producing demodulated audio at the primary of transformer
T2.
The secondary of transformer T2 feeds the audio signal into the emitter of Q10,
the first audio amplifier. This feeds the first stage of U3, a TL072 op amp. This
is configured as a high-gain bandpass filter, adding further selectivity to the
audio signal.
Audio peaks cause current conduction by Q9, the AGC detector. This charges
C33, and provides current to base of Q12, the AGC attenuator. Transistor Q12
is operated as a variable attenuator, controlled by its base current. This audio-
derived AGC loop is effective at attenuating and limiting large audio signals.
The audio signal is then fed through the volume control potentiometer R6, to the
second stage of U3, a unity-gain amplifier with an output buffered by
complimentary audio amplifier transistors Q13 and Q14. These transistors feed
the headphone though J2. The amplifier feeds the tip and ring connections of
the headphone jack, placing both headphone elements of a stereo headset in
series, reducing the current consumption of the amplifier.