Crystals with higher frequencies than about 30 MHz are almost exclusively overtone crystals. Such a crystal is intended to be used on an odd multiple of it`s fundamental frequency. Unfortunately, the crystal doesn`t want to resonate on it`s overtone frequency voluntarily, the oscillator circuit needs to force the correct overtone. For a little 2m
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band homebrew FM receiver I intent to use channel crystals and a first IF of 10. 7 MHz. After a while of thinking I determined taht I want the crystal (xtal) frequency to be defined by the following equation: Fxtal = (Freceive - 10. 7 MHz) : 3 For an initial lab test I had a hand full of crystals for the frequency 145. 625 MHz available. This frequency is more commonly used across Europe than here in the US. The crystal frequency is 44. 975 MHz and the crystal needs to be operated in 3rd overtone mode. If such a crystal is used in a regular oscillator, like for instance my crystal tester, the crystal will resonate on it`s fundamental frequency and not the intended third overtone. A little LC tank circuit can be used to get the crystal oscillator on the designated frequency. The tank circuits resonance frequency needs to be equal to the target frequency of the crystal oscillator. The exact frequency is not very critical as long as the resonance frequency is closer to the intended overtone frequency than to the fundamental mode frequency and other overtones. One possible approach is a series LC-Tank circuit in series with the crystal. This option works with almost every oscillator where the crystal is being used in series resonance. The oscillator works very reliable and always starts on the third overtone without any difficulties. I tested the circuit between about -20 and +40 degrees Celsius. In case you where wondering...
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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