This is a very straightforward circuit. The first stage acts as a crystal receiver. Use a germanium detector diode (like 1N34, but AA119 is much more common in Europe), a silicon one won`t do. The frequency is determined by L and C. For the FM band and VHF, wind a coil 5mm in diameter, 6-8 turns of coated wire 1mm thick. You can always vary the fr
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equency by spacing the turns a bit looser or tighter. C is much less critical. Something around 100p is preferable, though. The second stage is based around the versatile 2N3819 JFET high-impedance amplifier. With the 470k potentiometer you can adjust sensitivity of the circuit. The trimmer is used to zero the meter. Use any old 50mA or slightly smaller ammeter from the junk box. You can`t expect great performance from such a simple detector-based meter. Sensitivity is just adequate enough to get a basic idea of the power that your transmitter is capable of. Use the field-strength meter to find out when a transmitter is operating at optimal power. It can be very handy when aligning stages (like in case of the 4W transmitter) or experimenting with different antennas.
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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