Circuit Description - Ramsey Electronics QRP-80 Instruction Manual

build up the confidence that comes with actually making contacts and that they
do not need the additional challenge and pressure of low-power operation.
There is some wisdom in this view, but that opinion should not make
newcomers apprehensive about trying a Ramsey QRP transmitter, IF:
1. This is where your budget is.
2. You can count on somebody to help you with assembly.
3. You can count on somebody to listen to your signal during initial tests.
4. You have a reasonably good receiver.
5. You have space for a normal, no-compromise antenna for the band
you wish to operate, either a standard dipole, or the "inverted V"
dipole, or quarter-wave vertical.

CIRCUIT DESCRIPTION:

In brief, Q1 is a crystal oscillator, amplified by buffer stage Q2, which drives Q3
as the RF output amplifier. Q4 is a PNP keying circuit which opens and closes
the 12VDC supply line to Q1 and the T-R circuitry of D1 and D2.
S1 selects either of two crystals. R1,D3,D4 and L1 form a varactor controlled
series resonant circuit with the crystal. Adjusting R1 permits a crystal frequency
swing of up to 7 KHz, about the crystal frequency.
Q3 is a Class C RF amplifier that amplifies the RF output of Q2 to the final RF
power output level.
L6,C17 and C18 form a low pass filter (Butterworth) to match the output of Q3
to the antenna and reduce harmonics to acceptable levels as specified by the
FCC.
When the keying line is closed, Q4 conducts +12VDC to the oscillator stage,
applies a positive bias to the base of Q2 through R8, and +12VDC through
choke L4 to the anode of D1, which permits RF to pass through D1 to the filter
network while applying negative bias to D2 which blocks RF from passing to the
receiver. When the keying line is open, the +12VDC applied to D2 through R13
permits D2 to conduct from the antenna jack to the receiver jack. The buffer
and amplifier stages are not keyed, resulting in clean keying, free of chirps and
clicks.
QRP-80 • 10