The receiver is intended primarily for use with the remote control UHF transmitter described in the preceding article. It is a super-regenerative type with an active RF amplifier, T1. The antenna signal is applied to the input inductor via a BNC socket, The input circuit is tuned by trimmer C4.
The amplified RF signal is applied to the input of the super-regenerative stage based on transistor T2. Although the oscillator is, strictly speaking, not tuned, it will lock on to the amplified RF signal applied via coupling capacitor C7. The low-frequency modulation component is extracted from the oscillator signal with the aid of a low-pass filter, R6-C11-R7-C -12-R8-C13. The signal level at the demodulator output is 50 to 800 mVpp, so that further amplification is required before the signal can be applied to a digital input.
The inductors in the RF amplifier input and output are made from 1mm dia.silver-plated wire. The length of the pieces of wire is indicated by the component overlay. The wires run at a height of about 3 mm above the board surface. Note that the stator terminal of C4 is bent upwards and soldered direct to the input inductor. The same goes for junction C6-C, which is soldered ‘in the air’, directly on to the hot end of the inductor wire.
Inductor L1 consists of 12 turns of 0.6-mm dia. enameled copper wire. Its internal diameter is 3 mm.
Each of chokes L2 and L3 consists of 4 turns of 0.2-mm dia. enameled copper wire through a 3 mm long ferrite bead.
Capacitor C8 is a surface-mount technology (SMT) type which is fitted at the solder side of the board, as are the BFG65 and the BF980. The type indication printed on the transistors is legible from the component side of the board.
As indicated by the dashed lines on the component overlay, the super-regenerative section of the circuit must be screened from the rest. To do this, it is best to solder a 20 mm high box, made from tin plate, directly to the PCB copper surface.
Resistors:
R1 = 330 kΩ
R2 = 150 kΩ
R3 = 680 Ω R4, R6 = 3.9 k.Q. R5 = 120 IcS2 = 10 kS/ R8 = 33 Ic.C2 R9 = 8.2 IcE2
Capacitors:
C1 = 470 uF, 16 V radial
C2, C5, C9 = = 330 pF ceramic
C3 = 1 nF, coffinstyle leadless ceramic
C4, C6 = 10 pF trimmer
C7 = 12 pF, ceramic
C8 = 3.9 pF (surface mount)
C10 = 1 uF, 16 V, radial
C11 = 10 nF
C12 = 3.3 nF
C13 = 1 nF
Semiconductors:
T1 = BF980 or
BF966
T2 = BFG65
D1 = 1N4148
Inductors:
Construction details are given in the text 2 off 3-mm ferrite bead
0.6 mm dia. enamelled copper wire 0•2 mm dia. enamelled copper wire 1 mm dia. silver-Plated copper Wire
Miscellaneous:
K1•K2 = BNC socket
