VHF Public Service Monitor (Action-Band) Receiver in Software

Draw GTIN - 13 in Software VHF Public Service Monitor (Action-Band) Receiver

11

VHF Public Service Monitor Receiver: R1,R2,R3 10k ohm potentiometer R4,R8,R13,R21 47k ohm, 1 w, 5% resistor / 4 [yellow-violet-orange] R5 470 ohm, 14w, 5% / resistor [yellow-violet-brown] resistor [brown-gray-orange] / R22 2 ohm, 14w, 5% resistor [red-black-gold] C1,C6,C22 100 pF, 35 vdc disk capacitor [marked 100, 101, or 101K] C2,C5 10 pF, 35 vdc disk capacitor C3,C4 56 pF, 35 vdc disk capacitor C7,C8,C11,C20 001 F, 35 vdc disk capacitor [001 or 102 or 1 nF] C9,C10 15 pF, 35 vdc disk capacitor C13,C16,C17,C21 01 F, 35 vdc disk capacitor [marked 01 or 103 or 10 nF] C12 82 pF, 35 vdc disk capacitor C14,C32,C33,C35 100 to 220 F, 35 vdc electrolytic capacitor C15,C30,C36 47 F, 35 vdc electrolytic capacitor C18 220 pF, 35 vdc disk capacitor [marked 220 or 221] C19 22 pF, 35 vdc disk capacitor

R6,R9,R20 270 ohm, 14w, / 5% resistor [red-violet-brown] R7,R17,R19 10k ohm, 14w, / 5% resistor [brown-black-orange] R10 1 megohm, 14w, 5% / resistor [brown-black-green] R11,R12 1k ohm, 14w, 5% / resistor [brown-black-red] R14 33k ohm, 14w, 5% / resistor [orange-orange-orange] R15 470k ohm, 5% resistor [yellow-violet-yellow] R16 100k ohm, 14w, 5% / resistor [brown-black-yellow] R18 18k ohm,

1 w, / 4 1 w, / 4

C23,C24,C25 001 F, 35 vdc disk capacitor [001 or 102 or 1 nF] C26,C28,C29,C31 01 F, 35 vdc disk capacitor [marked 01 or 103 or 10 nF] C34 1 F, 35 vdc disk capacitor [marked 1 or 104] C27 10 F, 35 vdc electrolytic capacitor L1,L2 2-turn coil 5/32 OD dia - #24 ga Insulated magnet wire L3 L4 slug-tuned 3 12 turn / coil, see Table 11-3 450 kHz shielded quadrature coil, see Table 11-3 Varactor diode, BB505 [orange body marked BB505] 1N4148 signal diode 2SC2498 or 2SC2570A transistor

Misc PC board, battery holder, battery clip, speaker, etc Keep an ear on the local action from your easy chair with the VHF Public Service Receiver project, shown in Figure 11-1 The VHF Public Service Radio will allow you to tune the VHF high-band Police and Fire band, marine band, weather band, as well as railroad frequencies The receiver tunes any 5 MHz portion of the 136 to 175 MHz band Excellent performance, less than 1 uV sensitivity The receiver features: tuned input, low noise pre-amp stage with true dual-conversion superhet design with 2 pole Ceramic High Intermediate Filter or I-F and 6 pole ceramic low I-F filters! The receiver also features front panel volume, squelch, and tuning controls This is a great inexpensive receiver to put on your desk at home or to watch local radio activity while you are away from home on vacation or business trip

The heart of the VHF Public Service Receiver shown in the block diagram of Figure 11-2 is the MC3359

Q2,Q3,Q4 2N3904 transistor U1 U2 U3 Y1 SA602 8-pin IC MC3359 18-pin FM receiver IC LM386 8-pin audio amplifier IC 1024 MHz Crystal

FL1 107 MHz ceramic filter [brown, molded, 3 leads] FL2 450 kHz ceramic filter [black, square] S1 J1 J2 DPDT push switch PC mount RCA jack PC mount Figure 11-1 VHF public service receiver

integrated circuit The integrated circuit is a complete high gain low power FM IF sub-system which includes an oscillator, a mixer, a limiting amplifier, AFC, quadrature discriminator, op-amp, squelch, scan control and mute switch all combined in a single IC The MC3359 was designed to detect narrow-band FM signals using a 455 KHz ceramic filter Let s get into more details of the VHF Public Service Receiver by examining the schematic diagram shown in Figure 11-3 VHF signals from the antenna are amplified through the tuned input circuit (L1, C3 and L2, C4) by Q1, a microwave bipolar transistor Q1 s output is fed to the input of the SA602 IC, an efficient single-package (8-pin DIP) mixer-product detectoroscillator The tuneable oscillator section of the SA602

is aligned to operate at 107 MHz higher than the signal fed and amplified by Q1 For example, to receive 144-148 MHz signals, the oscillator must tune 1547 to 1587 MHz in order for the SA602 s mixing capability to produce a steady 107 MHz output signal to the rest of the circuit The oscillator frequency is determined by L3 and its associated capacitors, and varied by the varactor tuning network using D1 and varied by R1 The output from pin 4 of the SA602 passes through a ceramic 107 MHz filter, amplified by transistor Q2 and applied to input pin 18 of U2 Q3 provides AFC (Automatic Frequency Control) by keeping the local oscillator of U1 from drifting away from an incoming signal This is accomplished by tuning the varactor circuit in the direction opposite the drift