Ramsey Electronics QRP30 Manual de instrucciones descargar pdf (Pagina 8)

QRP30 • 8

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 5 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.

BLOCK DIAGRAM:

OSC.

BUFFER

FINAL

AMP

D1,D2

DIODE

SWITCH

C17.L5,C18

LOW PASS

FILTER

A B

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 23 24

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Ramsey Electronics QRP30 Manual de instrucciones Pagina 8