A very basic radio frequency detector, capable of detecting high frequency emissions in the lower GHz range, has gained attention recently. The detector, known as RF Detector w/ LM1458 op amp, has been circulating in books and on the internet for decades, but few have actually built this particular device. Intrigued by its potential, one individual decided to put it to the test.
The key component of this radio frequency detector is Capacitor C1. By shortening its pins, the performance of the device may be significantly improved. While the exact value of the capacitor doesn’t seem to be crucial, it should ideally be within the nF range.
To provide immediate feedback, a LM386 amplifier and a speaker can be connected to the OUT pin. However, there are other possibilities for utilizing the output signal, such as the example oscillogram photo.
The detector’s design consists of two stages of an LM1458 op amp. The first stage, along with two 100k resistors, functions as a supply splitter, ensuring the detector is powered by a 9V battery rather than a symmetrical voltage. The second stage acts as an inverting amplifier. Capacitors C3 and C4 provide capacitive coupling.
Several tests have been conducted using various devices emitting radio frequency waves, including a Raspberry Pi Pico W, a Bluetooth Low Energy module, and a mobile phone. It is worth noting that military and civil radar systems, such as those used at airports, also operate in the lower GHz regions. This opens up the possibility of detecting high-frequency sources with this device, in principle.
For those interested in a speaker variant, an LM386 amplifier can be used along with the detector. In this setup, the sound produced doesn’t need to be pleasant; it simply needs to be loud enough to hear. Consequently, most design guidelines for the LM386 IC can be disregarded in this case.
The RF Detector w/ LM1458 op amp offers potential for detecting high-frequency emissions in the lower GHz range. While it may not be a widely built device, it has piqued the interest of those who enjoy delving into the intricacies of radio frequency detection. As more individuals explore and experiment with this concept, it will be interesting to see how it evolves and if it finds practical applications beyond its current scope.
