A 2N3904 in the base circuit sets the `Q' point of the amplifier. FM subcarrier audio at 4.5 MHz is also injected at this point through a 3300 ohm resistor and a DC blocking capacitor. A high frequency 5-watt RF power transistor (2SC1909) serves as the last stage of the modulator. An NTE-235, NTE-236, or equivalent is suitable in this application. Clamped video is also fed into an LM311 voltage comparator that serves as a video sync detector. Some builders have used an LM1881 sync separator chip for this stage. Either way, sync pulses detected by this circuit trigger a CD4016B silicon bilateral switch that lowers the negative feedback around the video amplifier and voltage follower at sync time to compensate for high power gain compression in any solid-state linear power amplifiers that may follow the video modulated stages.
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Building an in-band, duplexed ATV repeater system is not a trivial task. Just ask anyone who's tried. The output spectrum of the repeater's transmitter must be extremely clean, and both the transmitter's output as well as the receiver's input must be tightly filtered to achieve adequate isolation and reject interference from strong signals on neighboring frequencies.
When the Brookdale ATV Repeater System was first constructed, a PC Electronics model RTX-70 exciter was used in the transmitter portion of the repeater. However, the intermodulation distortion products generated by the exciter when amplified by a Mirage D100ATV-R amplifier were so severe, they completely overwhelmed the repeater's receiver, despite the extensive combline and interdigital filtering used in the system.
After much study and research, the cause of the exciter's strong IMD products was found to be the result of distortion and non-linearity in the exciter's video modulator, and not the modulated RF stages themselves. Once the original video modulator was replaced with the one described on this page, the harmful effects of IMD were reduced to imperceptible levels. An added bonus was a noticeable increase in the exciter's RF power output.
This method of sync expansion is unique in that it also compensates for audio subcarrier compression at sync time, resulting in a clean output signal with no sync buzz in the transmitted audio. The first...
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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