By Diana Williams – Updated Mar 24, 2022
In the fast‑moving worlds of TV broadcasting and high‑speed Internet, ensuring a strong, clear signal is essential. A signal strength meter, or S‑meter, quantifies received signal power in decibels (dB), allowing you to fine‑tune your setup and diagnose issues.
The circuit we’ll build uses two operational amplifiers, three precision capacitors, two resistors, and a 74HC4040 binary counter IC. All parts are wired together on a breadboard for easy assembly and troubleshooting.
Begin by placing the three capacitors in a delta configuration, grounding one terminal. Connect one op‑amp in parallel with a resistor to the remaining two delta nodes, then join this network in series with the second op‑amp. Wire the second op‑amp to pin 10 of the 74HC4040. Power the IC from a DC source via pin 16 and ground it on pin 11. The signal to be measured enters the meter through pin 5. Trim leads if necessary so they fit snugly into the breadboard holes.
Attach the completed circuit to a BNC tee adapter at pin 5 of the IC. One arm of the tee goes to an oscilloscope, while the other receives the coaxial cable whose signal you wish to monitor.
Configure the oscilloscope’s horizontal and vertical controls so the waveform fills the display. A clean square wave indicates a shorted cable, whereas a stepped waveform confirms a healthy connection. The oscilloscope will also show the signal’s strength, frequency, and wavelength.
Use a 16‑AWG wire for optimal accuracy when connecting the components in your DIY signal strength meter.
