4SQRP Bayou Jumper 40 Meter CW Transceiver, Assembly & Instruction Manual

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revised 3 Feb 2021 Bayou Jumper revB Assembly Manual page 3 of 46
The receiver frequency is tuned by also using a reverse biased diode as a
varactor. The inductor L1 resonates against the sum capacitance of C20,
(optionally C20a) C30, and diode D3. Tuning is performed by potentiometer R8,
which varies the reverse bias voltage on D3, thus varying its capacitance.
The antenna is coupled to the detector through the grounded-base amplifier Q1,
a 2N3904. This amplifier also isolates detector oscillations, preventing them
from being radiated back through the antenna. An RF attenuator control, R1,
can be used to reduce the amplitude of strong signals that might overload the
receiver.
The detected audio appears at the source of the regenerative detector Q2, and
is coupled though capacitor C5 to audio preamplifier Q3, a 2N3904. Its output
is coupled to the volume control R6.
The output of the volume pot is amplified by the Audio Amplifier U1. This IC, an
NJM2113 is a low-noise headphone driver amplifier. Its balanced output feeds
the tip and ring contacts of the Headphone jack, J4. The shell contact is left
floating, placing the two headphone elements in series. This amplifier is also
capable of driving an external 8 ohm speaker.
A 6-volt regulator IC, U2, provides steady bias voltage to the low-level RF and
audio circuitry of the receiver, eliminating any tendency toward audio howl or
instability.
Switching between transmit and receive operation is performed with a rotary
switch SW1. This disables the receiver during transmit, and switches the
antenna between the transmitter and receiver sections. This switch also has an
OFF position, switching the antenna input to ground as well.
First Steps
Before getting started with building the kit, take some time to organize and
familiarize yourself with the parts provided and check them against the Bill of
Materials (pages 34 & 35). Building over a cookie sheet is recommended to
minimize the chance of lost parts. If parts are missing in your kit, send an email
to the kitter listed at
4SQRP.com . He will promptly provide replacements.