The intelligent discussion of VHF systems requires a feel for VHF systems, and how VHF energy moves through a system. At VHF, wavelength is very short. Wavelength in feet is F/983. 6, a typical 150 MHz system would have a quarter wavelength of 19. 8 inches. This does not include velocity factor of dielectric, or unevenly distributed series inductances
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or shunt capacitances, which can make electrical distance along a conductor appear much longer than it is. The general rule of thumb is two electrical degree length paths will have a negligible effect on system impedances. While that is 3 feet on 160 meters, two electrical degrees is roughly 1/2 inch on 150 MHz. A 10-inch long conductor, in particular a thin conductor with a dielectric, is just like having no path at all for VHF, yet we see Internet suggestions of adding thin wires from grid pins up to tuning capacitors to beneficially alter the path from tuning capacitor to grid in some amplifier layouts! This is the same false notion Johnson engineers used in the Valiant and Ranger transmitters. In the image below, Johnson used a buss wire to ground tuning capacitors to the 6146 socket ground, which turns out to be a disaster for ground loops and VHF harmonic suppression. A similar fallacy exists in HF amplifiers, where people add an even thinner and longer wire from tuning capacitors to the grid pins of tube sockets. A Kenwood TL922 I worked on had just such a mod, clearly the installer had no idea about wavelengths and transmission line behavior. They used a thin wire several inches long, shown below, in an attempt to reduce tuning capacitor to grid path impedance! VHF paths must be short and very wide, and ideally would be smooth surfaces. A wide path acts more like a groundplane, instead of a transmission line. For...
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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