The RF signal is split into two signals that are shifted 90 degrees out of phase (one plus 45 and one minus 45 degrees). Both are mixed to audio frequencies. The two audio signals are again shifted 90 degrees out of phase (again one plus 45 and one minus 45 degrees). When we add the two signals, one side band is in phase and added, the signals fro
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m the other side band are 180 degrees out of phase and substracted. The RF phase shift circuits are simple RC combinations, the trimmers are adjusted for maximum suppression at 3550 kHz. The disadvantage of such a simple phase shift network is that the side band suppression is a little frequency dependent. Both mixers are a CMOS switch. One 74HC4066 IC contains even four CMOS switches of which only two are used here! So a very simple and cheap solution for the mixer! At the input, you will find the very useful RF attenuator. It is the main volume control. The preselector is a bandfilter tuned to 3550 kHz. The RF preamplifier has some gain, a high input impedance for the bandfilter and a low output impedance for the phase shift networks. After this preamplifier we have the RF phase shift filters. It are simple RC networks, both tuned with the trimmers for approximately 45 degrees phase shift. They also compensate for amplitude differences. For optimum settings for phase and amplitude, it is possible that one network is plus 55 degrees, the other minus 35 degrees as long as the difference is 90 degrees. Adjust it by ear, try different trimmer settings while adjusting the other at 3550 kHz while listening to a signal on the suppressed side band. Usually, phase shifting is not done in the RF signal path but in the VFO. In that case, the VFO works at 4 times the reception frequency. The 90 degrees phase shift is obtained by...
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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