The first circuit is a simple preamplifier showing the power arangements for conveying DC to the amplifier via the coaxial cable. The second circuit is a small modification so the antenna can still be used for transmitting. The actual preamplifier in this circuit is a practical wideband amplfier that gives about 15 - 20dB of gain from 1. 8 MHz thro
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ugh to well over 200 MHz. You will no-doubt replace this circuit for your own favorite amplifier for the band you are interested in. The 2. 2mH chokes should have an absolute minimum reactance of 5000 ohms at the lowest frequency to be used. For 145 MHz these may simply consist of a few turns of wire. I personally used a 10-turn 4mm Dia. coil in series with a 2. 2mH torroidal inductor. The relay should have a coil resistance in excess of 1000 ohms and have tw1o-pole changeover contacts. When I built this circuit I used tw1o 5v PCB mounting relays, each having a single pole changeover contact. The relays each had a 560 ohm coil. If the DC power is switched OFF the preamplifier will become inactive and the relay will pypass the amplifier. In this manner it may be used with a low-power transmitter (typically up to 10 watts). My first switch was built inside the balun housing of a 2-metre beam antenna. Note that the DC 12 volts should NEVER be applied whilst transmitting or the poor little BFY91 will be blown to bits. There is also a short delay betw1een removing the DC and the preamp dropping out into a safe condition for transmitting
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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