As no one wants to listen to discriminator noise, the proper operation of the squelch circuit in any FM radio is vital. In a repeater, the squelch / COR is even more critical. The basic function of a squelch circuit is simple: detect the presence of a radio signal and turn the speaker audio on. That`s really all they do. The first FM squelch circu
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its worked by detecting the presence of a signal by measuring changes in the radios AGC (Automatic Gain Control) voltage. This method worked poorly on weak signals so a better method was developed, the noise operated squelch. The noise operated squelch works by measuring the amplitude of the discriminator white noise above the speech band. The phrase "above the speech band" is the critical part. Your receiver`s audio is split into two bands. One (from 300 to 3, 000 Hz) contains the speech. Everything above 5, 000 Hz is noise. No intelligence is carried there. When the radio hears a signal, the discriminator output begins to quiet. That is, the amplitude of the white noise above the speech band begins to drop. If we convert this AC high frequency noise to a DC signal, we can measure it. We can compare it to a known reference voltage as well. When the noise signal becomes weaker than the reference, the squelch circuit turns the speaker on. When the noise is stronger than the reference, the speaker is turned off. In practice we can add some timing as well. By adding a simple resistor / capacitor timing circuit to our squelch, we can keep it from opening on short bursts of noise that would be distracting. This still leaves one problem. You can`t have the squelch circuit close the audio immediately either. If you do, the audio from fluttering signals like mobiles would be badly chopped. This requires the squelch to have a time...
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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