Here is a nice little receiver for narrow-band FM reception. It can also be used to receive FSK, RTTY and PACKET signals from the HF bands. Basic receiver sensitivity is in the region of 1uV PD and the receiver can be tuned to almost any frequency from 100KHz up to probably 120MHz. It is a bit big and cramped, but I think you will have no difficulties reading it. The receiver is built on a single- sided PCB, which is quite unusual for this type of circuit. I do have a PCB available, but more about that later. The RF transformers T1 & T2 and the capacitor Cy are chosen for the frequency you are interested in. As an example, using re-wound IF transformers (from Antique Electronic Supply, Tempe) the former is about 3.5mm Dia. and 10 turns (thin wire) plus Cy=33pf tuned 26MHz to 35MHz. This covers CB, 10-meters and the radio control bands.
Click here to download the full size of the above Circuit.
Although the circuit looks quite complex it is really very simple. The first transistor is a harmonic oscillator so arranged that it will oscillate at any valid harmonic of the crystal. Replacing the crystal with a capcitor will result in VFO operation but the frequency stability is not so good. The oscillator and antenna tuned circuit, T2, are fed into a dual-gate FET where mixing takes place and produces the 455KHz IF. This is filtered by the CFK455 ceramic filter, amplified by the next two transistors and presented to the TBA120 (pins 13 & 14) which does all the rest. It delivers AF from the output, pin 8. Without the 10uf output capacitor you can see a DC shift corresponding to the frequency shift of the input signal. All NPN transistors can be replaced with almost any NPN transistor, such as the 2N2222 etc.
Due to the choice of IF, the wanted and image frequencies are only 910KHz away from each other. This means that with just one tuned circuit in the antenna circuit the image rejection will be poor for frequencies above about 20MHz. I thought that doesn't worry me because there are fewer stations above 20MHz to worry about. Image rejection is quite reasonable on the prototype at 14.1MHz but there was almost no image rejection at 100.455KHz. If you want a better image rejection at HF then I suggest you add another tuned circuit in the antenna circuit. Consider a converter circuit if you want to receive VHF or UHF...
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.....
characters left: