This is the story of the Fredbox, a rig that first saw the light of day in 1974 in Cambridge. In the last few months it has been restored to full working order to enjoy the renewed interest in AM operation on 2m in the UK. For several years I`d worked local stations with a simple very low power 10mW AM transmitter. This was coupled with a super-re
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gen receiver that first appeared in Practical Wireless in the late 1960s. Incidentally, this receiver design has just been republished in a recent copy. The simple combination was used on the bench with just a toggle switch change-over. For some time the antenna changeover consisted of unplugging the antenna from the receiver then plugging it into the TX and vice versa. The antenna at that time was a small dipole or indoor yagi rotated by hand. Combining these two circuits into one small handheld took only a couple of weeks. A small PCB was etched after a suitable box was found and the circuit worked first time. People working along side me were so impressed by its small size that very soon 3 other copies were made. The first Fredbox to Fredbox QSO was over about 0. 3kms. Local contacts were frequent around the Cambridge city area and the most regular QSOs were on 145MHz with a local disabled amateur, Fred, G8BWI. Because of this, the little box became know as the FREDBOX. I dedicate the circuit and the memories of those fun times to dear old Fred. How Fred could talk! Sometimes you`d start a QSO, then hand over to Fred, have your tea, and he`d still be talking away. Such good, fondly remembered, times indeed. The most exciting results took place away from Cambridge in Yorkshire and in South Devon. In Yorkshire the Fredbox was regularly used to make QSOs from my wife`s parent`s house in Barnsley up to Leeds about 20 miles...
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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