This project, based on an article published in the February 2008 edition of Radcom (the magazine of the Radio Society of Great Britain) is for a meter with a 50 ohm input impedance for measuring very small RF powers. Many RF power meters become inaccurate at low powers, but this meter is able to measure down to very low levels. From a theoretical
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standpoint, the meter is only able to accurately measure the power of steady, sine wave voltage RF - it would not be suitable for square wave signals for example. In practice, however, the most common requirement is to measure the power of sine wave signals and to compare power readings (when peaking up IF stages, for example). The reason that the meter is best suited to sine waves is that the circuit actually measures the peak-to-peak voltage in order to infer the power. The Radcom article explains how many RF `sniffer` type projects rely on detecting RF using a diode. This diode will require a certain amount of voltage to bring it into forward conduction, and this is the source of inaccuracy at low powers for more conventional designs. The original article gives details for a meter based on PNP transistors. I am more used to understanding circuits based on NPN transistors, so I first redrew the circuit diagram with NPN transistors and the diodes and PSU reversed. Once I had a good understanding, I realised that the design can be broken down into two sections; I call these the RF section and the DC voltmeter section. The RF part of the circuit is basically a dummy load with two detecting diodes to get the peak positive and peak negative voltages. A DC blocking capacitor is connected at the input, which acts as a short circuit at RF frequencies. What makes this design different is that the detecting diodes are driven into...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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