Schematic Symbol for an Integrated Circuit

 INTEGRATED CIRCUIT

INTEGRATED CIRCUIT 2

IC COUNTER

DEMULTIPLEXER - DEMUX

MULTIPLEXER - MUX

D FLIP FLOP

AND GATE

NAND GATE

OR GATE

NOR GATE

XOR GATE

XNOR GATE

NOT GATE

SCHMITT TRIGGER NOT GATE

OPERATIONAL  AMPLIFIER OP-AMP

MICROCONTROLLER

RASPBERRY PI

RASPBERRY PI MODEL B

RASPBERRY PI MODEL B GPIO

RASPBERRY PI A+ /B+ 2 AND ZERO GPIO

DIGITAL BUFFER

ARDUINO MEGA 2560

RASPBERRY PI PICO

What is symbols are commonly used on circuit diagram ?

FIXED RESISTOR

VARIABLE RESISTOR

POTENTIOMETER

THERMISTOR

LIGHT DIODE RESISTOR (LDR)

CAPACITOR (C)

VARIABLE CAPACITOR

TRIMMER CAPACITOR

POLARISED CAPACITOR

DIODE

ZENER DIODE

LED (LIGHT EMITTING DIODE)

PHOTODIODE

SCHOTTKY DIODE

RAIL

GROUND AND EARTH

An Active antenna for 160 to 4 meters

This active antenna has been doing its job in my loft for well over 10 years. l’'ve seen anumber of designs over the years, and this is the simplest, deriving from experiment. When | recently saw a highly sophisticated-looking commercial unit, | felt it was time to ‘go public’.
Active antennas rely on a combination of an antenna element (Such as a dipole, monopole, orloop) and anamplifier, which is the ‘active’ part. The antennaelementis non-resonant, and tends to be physically small. They have broad operating bandwidths, so don’t need to be tuned. In comparison, a resonant antenna would need tuner adjustments to cover the whole HF and lower VHF spectrum. So, the attraction of active antennas is convenience.
It is only fair to point out that some people dislike them, and there are pitfalls, which | shall point out. If you want a really excellent receiving antenna for all the HF amateur and broadcast bands, and have masses of space, why not put up a Beverage or rhombic antenna? If, as in my case, that’s out of the question, then consider an active antenna and, better still, try building your own! This one can be put together in a few hours and covers 160 to 4 metres.

DESIGN CONSIDERATIONS

THE CHOICE of a small antenna element (less than a tenth of a wavelength or so) is between the dipole and monopole, which respond to the electric field component of the radio wave; and the loop, which responds to the magnetic field component. A broadband active loop antenna is still on my list of things to try.
My first homebrew active antenna was a dipole, and was quite successful. The main thing it taught me was thatit’s nota good idea to have too much gain. It is natural to conclude that, as a short antenna picks up a smaller signal than a resonant dipole, the gain must be made up in the amplifier. Being a broadband device, the amplifier is subjected to the entire HF radio spectrum including powerful broadcast transmitters. What tends to happen in practice is that it distorts, generating intermodulation products. These appear to the receiver as additional signals and, though giving the impression of a ‘lively’ receiving system, are entirely unwanted. An attenuator between the active antenna and receiver is of no use at all, if the distortion has already happened in the active antenna.
It occurred to me to try asingle wire monopole, which made for a simpler amplifier. This worked and has been in use ever since.

CIRCUIT DESCRIPTION

THE AMPLIFIER, shown in Fig 1, is a source-follower circuit designed around Tr1, aJ310 FET (field-effect transistor). This has to present a high impedance to the small monopole, otherwise signal voltage is lost, and then deliver the signal to the receiver input, commonly a 50 Ohm impedance.

The FET has an output impedance in the region of 50 to 100 Ohm , which means that, if the FET source fed the receiver 50 Ohm input, more than half the signal voltage would appear across the FET, and less than half would be delivered to the receiver. That's where the transformer T1, in the source circuit, comes in. I used a quadrifilarwinding to give a 4:1 voltage step down ratio. This gives the source follower an overall gain of almost 1/5 in voltage (-14dB when the ratio of gate voltage to output voltage is expressed in decibels). The benefit of doing this is that the FET has much less work to do. The action of the transformer makes the impedance presented to the FET source bigger by a factor of 42 = 16 times, which is 800 Ohm. The result is improved linearity. Locations differ, but I have never known the active antenna produce unwanted signals. You may be concerned that this low gain would produce a rather 'deaf' receiving system but, from experience, comparing it to a transmitting dipole and tuner, you won't miss much, if anything. The internally-generated noise is very low, and the background noise in most of the HF spectrum is high. 

Power to the active antenna is fed via the coaxial cable, and the supply is injected via choke RFC1 housed in the power-feed unit near the receiver. R4 is included to limit the current in the event of an accidental short-circuit. An LED in series with the supply indicates that current is being drawn, and protects against inadvertent supply polarity reversal.

Shown on the circuit diagram is a power feed for a receiver. This is for the case where the receiver and antenna can share the same power supply. You may choose to omit it. The frequency response is shown in Fig 2, and is nominally flat to within 1dB to 60MHz and within 2dB to 100MHz

CONSTRUCTION 

TRANSFORMER T1 requires some care in construction, and is described in some detail, starting with the quadrifilar wire itself. This would probably be a labourintensive and expensive item to produce commercially, and is where the amateur's craft skills come into their own. Take four strands of 0.2mm diameter (35/36 SWG) enamelled copper wire, length approximately 300mm for each strand. Placing the wires side-by-side, clamp one end and, pulling the wires taut, fix the free end in the chuck of a hand drill. Turn the drill to twist the strands together. There is no need to twist too tightly, a few twists per centimetre being adequate. The core should be a high-permeability (greater than 100) ferrite toroid, 10 to 15mm in diameter. The purpose of the core is to produce a sufficiently high inductance to avoid gain roll-off at low frequencies, and given a high enough permeability, a wide variety of types, still to be found at rallies, should be suitable. If you are buying new, Table 1 shows the types that should be suitable. Supplier contact details are given at the end of the article. Between them, they should be able to source all items needed for construction. Wind seven or eight turns of the quadrifilar wire on the core. (Each time the wire passes through the core counts as one turn.) The photograph shows how this has been done on a T37 -61 core. To secure the winding, the core has been dipped in polyurethane varnish and left to dry. The individual wires need to be separated and the windings identified. Each wire end should be stripped of its insula tion. An easy way to do this is to hold the wire end in a blob of solder on the end of a soldering iron for a few seconds. Make sure you do this in a well-ventilated area and avoid inhaling the fumes or getting them in your eyes. The ends of each winding can then be identified with a multimeter or continuity tester. I found it useful to markthewindings with short strips of insulation stripped from ribbon cable, and slid overthe wires as shown in the same photograph. If you do this with three windings, the fourth can be left plain. Naming the windings arbitrarily 1 to 4, take the end of winding 1, and twist together with the start of winding 2. The end of 2 is then twisted with the start of 3, and so on. Twist fairly close to the toroid, and make electrical connection using the soldering iron, as described above, observing the precautions. The transformer is now complete. Check for electrical continuity through the whole transformer by measuring across the un-paired wires. Once the transformer is done, the rest of the construction is straightforward. Start with R2 as 47 Ohm  or 68 Ohm . It may need to be changed on test. The photograph shows my loft unit built into a diecast box, with a couple of solder tags for earthing to the box. Alternatively, the circuit can be built above a small piece of plain copper-clad board, which can then be fitted inside a weatherproof enclosure if outdoor mounting is required. The enclosure itself can be plastic - it is an antenna after all! Make sure you select the correct tap on transformer T1 for the output, and take care to prevent the unused taps from shorting to any other part of the circuit.

THE POWER FEED 

AS THE PHOTOGRAPH (right) illustrates, I built my power feed unit in a small plastic box. The choke isa single winding of around 20 turns on another high permeability toroid, which can be the same type as that used for the transformer. A metal enclosure would make sense for the power feed unit, since it will be near the receiver and possibly also domestic interference sources. If using a plastic housing, link the coaxial sockets with coaxial cable: I used some RG178. Keep the braid 'tails' short to avoid unwanted pickup.

TESTING AND COMMISSIONING 

CHECK CAREFULLY forwiring errors. For bench testing, the powerfeed and antenna units can be linked with a short coaxial cable. Having ensured that its voltage and polarity are correct, connect the power supply and check that the LED is lit. Measure the voltage across R2 and divide this by its resistance to find the current, or measure the supply current directly. This should be in the region of 10 to 20mA. I selected R2 for a current of around 15mA. Ifthe power feed output is now connected to a receiver, a small amount of additional hiss should be heard. Nothing should be heard until a short wire (1 metre or less) is placed on the antenna input. Signals should be heard on the HF bands, given suitable propagation conditions, or perhaps television or PC monitor timebase harmonics. The antenna unit should be installed as high and as far away from local sources of interference as practicable. Mine is at the apex of the loft, with an antenna wire of around 1 metre length, suspended from a hook in the highest beam. Avoid the temptation to increase the wire length excessively in order to increase the signal. This brings the risk of distortion, and departure  
from a flat gain with frequency. 

POSITIVE - EARTH VERSION 

WITH A NEGATIVE supply and positive earth, a couple of components can be omitted. This is shown in Fig 3, below. However, note that, while this is fine on its own, it must not be connected to a receiver with a negative earth, because this shorts out the supply

=* by Ian Braithwaite, G4COL *= 

Directional Antennas

It has already been mentioned that ideal omnidirectional antennas cannot be produced in reality. Nonetheless only antennas that focus their radiated power in a particular spatial direction can properly be called directional antennas. At an equivalent transmit power, they significantly improve the signal-to-noise ratio, but must be aligned on the distant station so that in many cases a rotation facility has to be used. For directional antennas the parameters gain, directivity and all values associated with the radiation pattern, like front-to-back ratio, side-lobe suppression or half-power beamwidth as already discussed give an overview about how much the radiated energy is focused into a certain direction. The simplest form of a directional antenna is a setup of two monopole antennas at a predefined distance, which are fed with different phase

Principle of a directional antenna

In the example a distance of a quarter wavelength and a phase difference of 90° have been chosen, resulting in a cardioid shaped radiation pattern when the far field strengths generated by the two individual antennas are added.

Cardiold shape radiation pattern

Even though this configuration does not produce strongly focused radiation, it however exhibits a sharply defined null towards the backside which can effectively be used to suppress interfering signals. By superimposing the diagrams obtained by combining two or several radiators arranged at defined distances and with defined phase shifts, directional patterns can be generated whose directivity is limited mainly by the available space to setup the number of required radiators. Instead of feeding the radiators via cables , the principle of radiation coupling is mostly applied in practice, with only one radiator being fed from the cable and the remaining elements activated by this radiator. Yagi-Uda antennas, which are commonly used for the reception of TV and VHF sound broadcast signals, have typically between 4 and 30 elements and yield gain values of 10 dB and more. The possibility of changing the direction of the main beam of a highly directive antenna by purely electronic means is utilized to an increasing extent also with antenna arrays for very high frequencies (e.g. for satellite radio services). The antennas used are referred to as planar antennas and mostly consist of a dipole curtain which, in contrast to curtain antennas, is installed in front of a conductive plane. This array can also be implemented by etching the radiators as tracks into a printed circuit board (microstrip antenna). In this way, even large arrays of antennas can be implemented for the microwave frequency range with high precision and efficiency.

=* by Rohde & Schwarz*=

What is the basic principle of antenna?

An antenna is defined by Webster‘s Dictionary as ―a usually metallic device (as a rod or wire) for radiating or receiving radio waves.‖ The IEEE Standard Definitions of Terms for Antennas (IEEE Std 145–1983) defines the antenna or aerial as ―a means for radiating or receiving radio waves.‖ In other words the antenna is the transitional structure between free-space and a guiding device. The guiding device or transmission line may take the form of a coaxial line or a hollow pipe (waveguide), and it is used to transport electromagnetic energy from the transmitting source to the antenna or from the antenna to the receiver. In the former case, we have a transmitting antenna and in the latter a receiving antenna.

An antenna is basically a transducer. It converts radio frequency (RF) signal into an electromagnetic (EM) wave of the same frequency. It forms a part of transmitter as well as the receiver circuits. Its equivalent circuit is characterized by the presence of resistance, inductance, and capacitance. The current produces a magnetic field and a charge produces an electrostatic field. These two in turn create an induction field. 

Definition of antenna 

An antenna can be defined in the following different ways: 

1. An antenna may be a piece of conducting material in the form of a wire, rod or any other shape with excitation. 

2. An antenna is a source or radiator of electromagnetic waves. 

3. An antenna is a sensor of electromagnetic waves. 

4. An antenna is a transducer. 

5. An antenna is an impedance matching device. 

6. An antenna is a coupler between a generator and space or vice-versa.

source : https://www.sathyabama.ac.in/sites/default/files/course-material/2020-10/SEC1301.pdf

Electromagnetic Radiation

Electromagnetic Radiation is energy in the form of a wave of oscillating electric and magnetic fields, the wave travels through a vacuum at a velocity of 2.998 x 10^8 meters per second (186,284 miles per second). The Wavelength of an electromagnetic wave determines its properties , x-rays , infrared , microwaves , radio waves and light are electromagnetic radiation. 

                                                             WAVELENGTH

Electromagnetic radiation (EMR) is a form of energy that surrounds us in various forms and has profound effects on our daily lives, scientific research, and technological advancements. It is energy that travels and spreads out as it moves—taking the form of visible light, radio waves, microwaves, X-rays, and other wavelengths on the electromagnetic spectrum. In this article, we’ll delve deep into what electromagnetic radiation is, how it works, its different types, and its applications and impacts on human life.

What Is Electromagnetic Radiation?

Electromagnetic radiation is composed of electric and magnetic fields that oscillate perpendicular to each other and the direction of the energy's travel. This dual-wave nature allows EMR to move through the vacuum of space as well as through various materials. Unlike sound, which needs a medium (like air or water) to travel through, EMR can move through empty space.

The Nature of Electromagnetic Waves

Electromagnetic radiation has both particle-like and wave-like properties, a duality explained by quantum mechanics. Each particle of electromagnetic radiation is known as a photon, which travels at the speed of light (approximately 299,792 kilometers per second in a vacuum). Photons have no mass but possess energy and momentum, which makes them unique. The amount of energy they carry depends on their frequency—the higher the frequency, the more energy each photon carries.

The Electromagnetic Spectrum

The electromagnetic spectrum encompasses all types of electromagnetic radiation. The spectrum is typically divided into seven major categories based on wavelength and frequency:

1. Radio Waves (low frequency, long wavelength): Used in communication systems such as radios, televisions, and cell phones.

2. Microwaves: Employed in microwave ovens, radar, and satellite communications.

3. **Infrared Radiation**: Used in night vision equipment, remote controls, and thermal imaging.

4. **Visible Light**: The only part of the spectrum visible to the human eye, encompassing all colors from violet to red.

5. **Ultraviolet (UV) Radiation**: Naturally emitted by the sun, can cause skin burns and is used in sterilization.

6. **X-Rays**: Commonly used in medical imaging to view bones and other structures inside the body.

7. **Gamma Rays**: Extremely high-energy waves produced by radioactive atoms and certain astronomical processes, used in cancer treatment and scientific research.

Each type of radiation on the spectrum has distinct applications, properties, and effects.

Properties of Electromagnetic Radiation

The characteristics of electromagnetic radiation include its **wavelength**, **frequency**, and **speed**.

- **Wavelength** is the distance between two peaks (or troughs) of a wave. The longer the wavelength, the lower the frequency.

- **Frequency** is the number of wave cycles per second, measured in hertz (Hz). High-frequency waves carry more energy.

- **Speed** of EMR in a vacuum is constant at approximately 300,000 kilometers per second, though it can slow down when passing through different media like glass or water.

How Electromagnetic Radiation Works

The behavior of electromagnetic radiation can vary depending on its wavelength and the type of material it encounters. EMR can be **reflected**, **refracted**, **absorbed**, or **scattered**.

- **Reflection** occurs when EMR bounces off surfaces, like light reflecting from a mirror.

- **Refraction** happens when EMR passes through a medium and changes direction, which is why objects look distorted when viewed through water.

- **Absorption** is when a material takes in the energy of the EMR, as seen when sunlight warms the skin.

- **Scattering** occurs when EMR is forced to deviate from its straight path, often by particles in the atmosphere.

### Applications of Electromagnetic Radiation

Electromagnetic radiation is indispensable in both science and technology. Here’s a closer look at some of its uses:

#### Communication

Electromagnetic radiation, particularly in the radio and microwave parts of the spectrum, is essential in communication. Radio waves transmit audio, television, and data signals. Microwaves are used in mobile networks, Wi-Fi, and satellite communications.

#### Medicine

In the medical field, X-rays are pivotal in imaging bones and tissues, while gamma rays are used in radiotherapy for cancer treatment. UV radiation can also be used to sterilize medical equipment. Infrared technology aids in heat-based therapies and infrared saunas.

#### Industry

EMR finds widespread industrial applications. For instance, infrared waves are used in thermal cameras to detect heat leaks and insulation issues. UV radiation is used in curing adhesives and coatings in manufacturing processes, while lasers (highly focused EMR) are used in cutting and welding metals.

#### Astronomy and Space Exploration

Astronomers rely on EMR to study distant galaxies, stars, and other celestial bodies. Different types of radiation, from radio waves to gamma rays, provide insights into the universe’s structure, formation, and evolution.

#### Everyday Devices

Our daily lives are filled with devices that rely on EMR. Microwaves cook food, remote controls operate TVs using infrared signals, and smartphones and laptops communicate via Wi-Fi signals. Even visible light—the lightbulbs in our homes—are forms of electromagnetic radiation.

### Effects of Electromagnetic Radiation on Health

Electromagnetic radiation’s effects on human health depend on the radiation type, intensity, and duration of exposure.

#### Non-Ionizing Radiation

Radio waves, microwaves, and visible light fall under **non-ionizing radiation**, meaning they don’t have enough energy to remove tightly bound electrons from atoms. This type of radiation is generally considered safe in low doses. However, prolonged exposure, especially to high levels of microwave radiation, can cause heating effects and potential tissue damage, which is why microwave ovens have shielding.

#### Ionizing Radiation

Ultraviolet rays, X-rays, and gamma rays are forms of **ionizing radiation**. This radiation has enough energy to ionize atoms and molecules, potentially damaging DNA and causing mutations. Prolonged exposure to ionizing radiation can lead to serious health issues like cancer. For instance, excessive exposure to UV radiation from the sun can cause skin cancer, which is why sunscreen is recommended.

Medical imaging procedures that use X-rays are generally safe due to the controlled doses, but frequent or prolonged exposure should be avoided.

### Safety and Protective Measures

Given the potential hazards of electromagnetic radiation, several safety guidelines and protective measures are in place:

- **Limit exposure to high levels of EMR**: Medical professionals take precautions during X-ray procedures, such as using lead shields to protect patients and personnel.

- **UV Protection**: Applying sunscreen, wearing sunglasses, and limiting direct sun exposure can protect against UV radiation.

- **Microwave Oven Safety**: Microwaves are designed with shielding to contain radiation. It’s advisable to avoid standing directly in front of a microwave while it's operating.

- **Safe Distance from EMR Sources**: Avoid prolonged use of cell phones and keep devices at a distance during sleep.

- **Regulations and Standards**: Regulatory bodies such as the International Commission on Non-Ionizing Radiation Protection (ICNIRP) set limits for EMR exposure, especially for workers in industries where EMR exposure is a risk.

### Future Developments in Electromagnetic Radiation Research

As technology evolves, the study of electromagnetic radiation continues to advance. Scientists are exploring new ways to harness EMR safely and efficiently in fields such as:

- **Quantum Computing**: Quantum computers rely on the properties of EMR to manipulate quantum bits (qubits) and perform complex calculations.

- **Advanced Imaging Techniques**: Researchers are developing methods to use EMR more effectively in imaging technologies, allowing for non-invasive diagnostics and early disease detection.

- **Green Energy Solutions**: Solar power, which harnesses EMR from the sun, is becoming an increasingly popular and sustainable energy source.

- **Wireless Power Transmission**: Electromagnetic radiation is being studied for its potential to wirelessly transmit power, eliminating the need for wires and enabling more versatile power solutions.

### Conclusion

Electromagnetic radiation is one of the most critical forces in our universe, playing a significant role in natural phenomena and technological advances. From visible light that allows us to see to radio waves that enable global communication, EMR affects virtually every aspect of modern life. While certain types of EMR, like gamma rays and X-rays, require careful handling to prevent harm, others are indispensable in healthcare, communication, and entertainment.

Understanding EMR and its applications, alongside the potential health risks, is essential in a world increasingly reliant on electronic devices and communication networks. With ongoing research and evolving safety standards, the future holds promising possibilities for harnessing electromagnetic radiation safely, efficiently, and innovatively.

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This should give you a good foundation on electromagnetic radiation. For specific subtopics or additional details, feel free to ask!

Electromagnetic Spectrum

nm = nanometer  ( 1 nm = 0.000000001 meter)

u    = micrometer ( 1 u    = 0.000001 meter)

mm= millimeter    ( 1 mm= 0.001 meter)

m   = meter          ( 1 m   = 39.37 inches)

km = kilometer     ( 1 km = 1000 meters)