Popular Electronics Heterodyne Detector

Last updated Sun Sep 10 18:10:59 EDT 2000

Schematic Diagram


eagle sch file*.

*Eagle is a layout editor from CADSoft, a freeware version is available (Win & Lin)

Parts List

IC1        567 phase-locked loop, integrated circuit
U1         LM386 audio power amplifier, ic
Q1, Q2     2N391M NPN transistor
Q3         MPF102 JFET transistor
(All fixed resistors are 1/4 watt, 5% units.)
R1, R2        220,000 ohm
R3-R6         2,200 ohm
R7            1,000 ohm
RS, R14       270 ohm
R9            100,000 ohm
R10           4,700 ohm
R11           10,000 ohm
R12           50,000 ohm, potentiometer
R13           10,000 ohm, potentiometer

C1, C2, C5        0.01 microF, Mylar
C3                0.047 microF, Mylar
C4                0.0022 microF. Mylar
C6, C7, C11, C12  0.1 microF, ceramic-disc
C8                10 microF, 16 WVDC, electrolytic
C9                47 microF, 16 WVDC, electrolytic
C10               470 microF 16 WVDC, electrolytic
SG1               Piezo tweeter (Ultrasound receiver)
Power source, headphones or speaker, wire, solder.


The bat ultrasounds are picked up by the microphone SPKR1 and go through two stages of amplification at Q1 and Q2.
Separately, a tunable (R12) single frequency is produced by the LM567 oscillator U1. The LM567 is a tone decoder but here its input is grounded and its voltage controlled oscillator is used as a precision oscillator. The oscillator frequency is given by
    f = 1/(1.1*C4*(R10 + R12))
      = 1/(1.1*0.0022*10-6*(4.7 + [0-50])*103)
      = [88-7.5] khz
The two signals are mixed at Q3 to produce both a signal in the audio range and higher frequencies that are then filtered out.
The remaining audio signal undergoes a last stage of controlled (R13) amplification with the LM386 at U2 before being available for output at AUDIO OUT.
The power source is a simple 9V battery, so this instrument is completely portable.

Ultrasound Receiver

RadioShack Cat.#: 900-6064 ($4.95)

A small 40 Khz ultrasound receiver (Velleman / MA40A5R). The bandwith of these piezo-transducers has a narrow peak around 40 khz. A group of students at UNN has measured it.

transducer photo

LMC567 Oscillator

"The LMC567 is a low power general purpose LMCMOS[tm] tone decoder which is functionally similar to the industry standard LM567. It consists of a twice frequency voltage-controlled oscillator (VCO) and quadrature dividers which establish the reference signals for phase and amplitude detectors. The phase detector and VCO form a phase-locked loop (PLL) which locks to an input signal frequency which is within the control range of the VCO."

Fairchild CD4024.
datasheet (pdf)


LM386 audio amplifier

"The LM386 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value up to 200."

National LM386
datasheet (pdf)