This transmitter had its origins as a conventional shunt fed Hartley oscillator for 80 meters using a pair of 27 triodes connected in parallel; with 300 VDC on the plates of the 27`s, I was able to get about 4 watts output ( with decent stability ) for about 18 watts input, about 23% efficiency. Here is a schematic of the oscillator by itself: Thi
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s circuit will work fine as shown as a stand-alone transmitter. Circuit parameters are as follows: 15K grid leak; tank circuit: 12 turns, 1/4" copper tubing, 2. 5" diameter, about 4. 75" long, with 540 pf padding capacitance ( tub micas ) and a 60 pf tuning capacitor. For an antenna coupler, I used a 250 pf variable capacitor in series with a coil consisting of 40 turns 18 Awg insulated wire wound on a 2. 5" diameter black PVC pipe. I put taps at 10, 20, 30, 35, and 40 turns. This will tune a 1/4 wave end fed antenna ( marconi antenna), which for 80 meters, is about 67 feet. Incidentally, I use the same tuner, in parallel configuration, to tune this same antenna as a 40 meter "half-wave". The coupler is simply placed in inductive proximity to the tank coil- don`t couple the antenna too heavily or the "note" will suffer with this circuit. There is an optimal coupling point whereby stability is good and yet useful output power is developed. Trial and error required here. Inspired by a George Grammer article in a February 1931 issue of QST magazine, "More power with better frequency stability", I decided to build a MOPA ( Master Oscillator Power Amplifier ) using the two type 27s in parallel to drive a single 865 tetrode. Both tubes were available in 1929, and both are still relatively easy to find and inexpensive. Here is a schematic of the 865 power amplifier: The Hartley oscillator is coupled to the grid of the 865 thru a...
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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