VHF-UHF RF Sniffer

This is a multi-chapter instruct able. I will be describing the making of a short/medium range RF remote-control using the UHF 433Mhz frequency. It´s impossible to setup & adjust a RF transmit-receive link if you are not sure the transmitter is working properly. At 433MHz, your multi meter or even a regular oscilloscope are totally useless.
In this chapter (1) I will show you this ultra-simple RF sniffer circuit with which you can visualize with an LED:
(1) if the transmitter is oscillating.
(2) its relative power output by the brightness of LED.
(3) check the frequency of the oscillator with a simple school ruler by measuring the distance between nodes (as did Ernst Lecher 120 years ago ) https://en.wikipedia.org/wiki/Lecher_lines .At 433MHz, distance between nodes (0-crossing points) is 323mm on copper wire (half wavelength).
VHF-UHF RF Sniffer
UHF comprises frequencies between 300Mhz and 3Ghz. At these frequencies the physical layout of the components is crucial; the same circuit may work or not depending on how it´s built. A single millimeter of wire or component lead is an inductor and affects the circuit. You cannot use a solder less breadboard because it´s plagued with parasitic capacitances and inductances which at UHF frequencies (and VHF) behave as actual components. To avoid crosstalk between traces & ground loops UHF circuit must share a common ground plane (e.g.:, double sided PCB) to which all ground points are connected (https://en.wikipedia.org/wiki/Ground_plane ).
On the good side, UHF inductors are of low values and are usually air-core and made with few turns of wire or even printed on the PCB. The same applies for antennas: at 433Mhz a 1/4 wave antenna is only 17cm long. Capacitor values are also very low. All these properties translate into a very small & economical circuit.

Step 1: Overview

circuit is built on a small single sided board.

Step 2: Circuit Diagram & Main Components

Q1: 2SC3358 npn RF transistor

VR1: 10kohm potentiometer

Bat: CR2032 3V battery & socket

Antenna: 10 cm wire (approx.)

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