Schematic diagram for the Ramsey HR-40 CW/SSB Direct Conversion Receiver. Ramsey Electronics Inc
Figure shows the circuit for the HR-40 Direct Conversion Receiver for 40 meters. Here’s how this circuit works. The incoming signal from the antenna is coupled through C5 and the RF gain control R1, to antenna input transformer L1. (A 10.2-MHz IF transformer, detuned to cover the 40-meter band, can be substituted.) This “tuned” transformer peaks the desired signal and applies it to the NE602’s mixer section. The shielded oscillator coil, L2, along with varactor diode D1, R2, R5, C1, C2, C3, and
C4, form an oscillator network with the NE602’s internal oscillator. Rotating R2 varies the oscillator’s frequency over a tuning range of about 250 kHz. The NE602 mixes the incoming RF signal with the signal from the internal oscillator to produce an audio signal at Pin 4. The output audio signal is coupled to the LM 386 audio amplifier via coupling capacitor C8 and volume control R3. Capacitor C9 boosts the voltage gain of the LM386 to about 50. The high-level audio output is coupled from Pin 5, U2, to external headphones or a low impedance (4 to 8 ohms) speaker through coupling capacitor C12 and output connector J2.NE602.
An internal 9-volt transistor battery (or an external power source of about 9–12 Vdc, 60 mA) is used to power the HR-40. Note that zener diode D2, along with C10 and R4, form a 6.2-Vdc voltage regulator network to improve stability of the NE602’s internal oscillator circuit.