By the addition of one integrated circuit and some passive components, I was able to convert my earlier developed 40-meter direct conversion receiver design into a superhet model. Anyone who has listened to 40 meters during the evening hours on the crowded 40 m band will appreciate the advantages of the single signal reception, which this circuit
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offers. All simple direct conversion receiver designs suffer from degraded selectivity performance and are more subject to overload by contrasted to even modest superhet designs. Direct conversion designs are simpler by contrast because they are missing an IF stage and any associated filtering, a BFO and the second mixer. In order to modify the design to create a superhet model, it was necessary to increase the 1st oscillator frequency from 7000 kHz - 7040 kHz to a revised range of 10686 kHz -10731 kHz (operating frequency plus the intermediate frequency). The choice of this 1st oscillator frequency turned out to be fairly easy by considering the availability of 3686 kHz crystals. Bandwidth is set to 200 Hz by a series coupled filter (using a single 3686 kHz crystal) in the IF amplifier section. This choice is highly suitable for CW operation. The choice of 3686 kHz IF allows use of readily available 10. 7 mHz ceramic resonator in the 1st oscillator circuit. The first part of the circuit to be described is the 1st oscillator (main tuning). It is a variation of the Colpitts type oscillator. It uses a 10, 7 ceramic resonator as its frequency-determining component. Unlike a quartz crystal based VXO, the ceramic resonator Q1 results in a much broader tuning range (approximately 45 kHz) while still maintaining a desired level of frequency stability at the same time. A second ceramic resonator with a center frequency of 7020 kHz...
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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