Magnetic Classification of Materials
What Are the Magnetic classifications of Materials?

Material Type Description

Nonmagnetic No magnetic reaction.

Diamagnetic Induced dipole moment opposes applied field.
Repelled by bar magnet.
Very weakly magnetic.

Paramagnetic Induced dipole moment aligns to applied field.
Attracted by bar magnet.
Weakly magnetic.

Ferromagnetic Induced dipole moment aligns to applied field.
Attracted by bar magnet.
Very strongly magnetic.
Has memory and so can be used to create permanent magnets.
High electrical conductivity.

Ferrimagnetic Type of ferromagnetic material.
Induced dipole moment aligns to applied field.
Attracted by bar magnet.
Very strongly magnetic.

Ferrites Type of ferrimagnetic material.
Induced dipole moment aligns to applied field.
Attracted by bar magnet.

Very strongly magnetic.
Low electrical conductivity.

Superparamagnetic Material mixture: ferromagnetic particles suspended in a plastic binder.
Induced dipole moment aligns to applied field.
Very strongly magnetic.
Has memory, which allows for uses in audio, video, and data recording.


What are the dangers of radio frequency (rf)  and microwave exposure to humans?
Dangers to Humans of Radio Waves and Microwaves.

We can define the potential hazards of RF radiation in terms of:

1 Direct effects on people
(a) Thermal effects attributable to the heating of the human body due to the absorption of RF energy. At lower frequencies this includes heating due to excessive current densities in some parts of the body.

(b) Shocks and burns which may result from contact with conductive objects, e.g. scrap metal, vehicle bodies, etc., located in electromagnetic fields.

(c) The so called ‘athermal’ effects, if any, where it is postulated that the fields act directly on biological tissue without any significant heating being involved.

2 Indirect effects on people
Effects on people wearing implantable devices such as heart pacemakers, insulin pumps, passive metal plates and other related hardware due to interaction with some aspect of the implantable device. Some effects in this category affect the quality of life rather than physical health, e.g. interference with hearing aids and other electronic devices.

3 Effects on things in the environment
Ignition of flammable vapours and electro-explosive devices, e.g. detonators

Interference with equipment
Category 3 above may, of course, also involve people who may be present near the subject and may be affected by fire or explosion, people in aircraft where critical equipment is interfered with and the aircraft may be in jeopardy.

With the widespread use of mobile phones risks extend to interference with critical medical equipment in hospitals. Hence many people are likely to be affected in some way ranging from these obvious examples down to the merely irritating cases of interference with computers and domestic radio sets.

Before proceeding it is worth noting that a perceived ‘effect’ is not necessarily synonymous with ‘harm’ or ‘injury’. Our environment affects our bodies daily and some effects are of value, some harmful, and some have no apparent effect.

Some aspects of these topics may be differentiated in a general way in relation to the frequencies involved. Standards do tend to differ considerably in the detail of these.


An Introduction To Microsoft Hololens.
What is Microsoft Hololens?

Microsoft’s vision for the future is, it’s fair to say, one that not too many of us were expecting. Launched during the Windows 10 keynote with all the cloak and dagger reveal of a Jobsian ‘one
more thing…’ it became the headline story of the talk. this was undeniably a curve ball from the redmond giant.

But what kind of curveball exactly? Well, what it definitely is not is microsoft’s take on google glass.
holoLens is not an optical hUd and, while glass Explorers might be ridiculed and even viciously beaten for ‘exploring’ in public, you’d almost certainly be arrested if you approached a bank cashier wearing holoLens.

Yet that’s nothing to the trouble you’d be in should you even step near a petrol station or jittery downtown corner shop wearing oculus rift. Awesome it is. pretty it ain’t. and while it’s of closer comparison to holoLens than glass is, it’s still not quite the direct competitor to microsoft’s offering.

Rift locks you into a wholly virtual world whereas microsoft embraces the real world, showing its users pinning apps to living room walls and tinkering with projections of motorcycles.

Microsoft has effectively produced a micro pc that is hooked up to a set of high-definition holographic lenses, which it projects its 3d experience on 19 to. this, combined with spatial sound technology, creates wholly immersive Vr that promises to redefine Windows 10 apps… if the launch video is to be believed, anyway.

And that’s what’s making us very excited. Early hands-on reviews with development units have been both positive and profound. seen-it-all before technology journalists are genuinely excited about holoLens’s commercial, creative and educational potential.


How good is Panasonic CX850 TV?

Panasonic is really cranking the 4K at the moment, firstly with a slew of impressive 4K tVs, and secondly with the fact that it will introduce a range of 4K gadgets to support its panels, including a player that enables you to watch 4K content on and 4K cameras.

But ultra high-definition wrangling aside, the most exciting thing about panasonic’s tVs – specifically, its flagship 55-inch 4K LEd cX850 screen – is not so much what’s on the outside, but what’s on the inside.

Unlike the majority of television manufacturers, who are implementing android tV into their boxes, panasonic has made a shrewd move and plumped for the Firefox tV operating system.

Ignoring, for a moment, whether you prefer browsing the web via chrome or Firefox, mozilla’s os looks pretty spectacular, with an intuitive feel that makes it easy to find your way around and access the myriad of content – and voice command capabilities will further enhance this.

The new OS will also come with a range of extra nifty features, such as the ability to wirelessly exchange content like photos and videos from a smartphone, tablet or pc; and apps designed to notify you of new events, much as they would on a mobile.


What is small loop antenna?
Small loop antenna defined.

Large loop antennas are those with overall wire lengths of 0.5λ to more than 2λ. Small loop antennas, on the other hand, have an overall wire length that is much less than one wavelength (1λ).

According to a Second World War US Navy training manual such antennas are those with an overall length of ≤0.22λ. Jasik’s classic 1961 text on radio antennas uses the figure ≤0.17λ, while John Kraus (1950) used the figure ≤0.10λ.

An amateur radio source, The ARRL Antenna Book, recommends ≤0.085λ for small loop antennas. For the purposes of our discussion we will use Kraus’s figure of ≤0.10λ.

A defining characteristic of small loops versus large loops is seen in the current distribution. In the small loop antenna the current flowing in the loop is uniform in all portions of the loop. In the large loop, however, the current varies along the length of the conductor, i.e. there are current nodes and antinodes.

The small loop antenna also differs from the large loop in the manner of its response to the radio signal. A radio signal is a transverse electromagnetic (TEM) wave, in which magnetic and electrical fields alternate with each other along the direction of travel.

The large loop, like most large wire antennas, respond primarily to the electrical field component of the TEM, while small loops respond mostly to the magnetic field component. The importance of this fact is that it means the small loop antenna is less sensitive to local electromagnetic interference
sources such as power lines and appliances.

Local EMI consists largely of electrical fields, while radio signals have both magnetic and electrical fields. With proper shielding, the electrical response can be reduced even further.


How to calculate the capacitance of coaxial cable?
Coaxial Cable Capacitance Calculation Explained.

A coaxial transmission line possesses a certain capacitance per unit of length. This capacitance is defined by:

C = 24ε / log(D/d)          pF/Metre

C is the capacitance
D is the outside conductor diameter
d is the inside conductor diameter
ε is the dielectric constant of the insulator.

A long run of coaxial cable can build up a large capacitance. For example, a common type of coax is rated at 65 pF/metre. A 150 metre roll thus has a capacitance of (65 pF/m) (150 m), or 9750 pF. 

When charged with a high voltage, as is done in performing breakdown voltage tests at the factory, the cable acts like a charged high voltage capacitor. 

Although rarely if ever lethal to humans, the stored voltage in new cable can deliver a nasty electrical shock and can irreparably damage electronic components.


What is transmission line noise?
Transmission Line Noise Defined.

Transmission lines are capable of generating noise and spurious voltages that are seen by the system as valid signals. Several such sources exist.

One source is coupling between noise currents flowing in the outer and inner conductors. Such currents are induced by nearby electromagnetic interference and other sources (e.g. connection to a noisy ground plane).

Although coaxial design reduces noise pick-up compared with parallel line, the potential for EMI exists. Selection of high-grade line, with a high degree of shielding, reduces the problem.

Another source of noise is thermal noise in the resistances and conductances of the line. This type of noise is proportional to resistance and temperature.

There is also noise created by mechanical movement of the cable. One species results from movement of the dielectric against the two conductors.

This form of noise is caused by electrostatic discharges in much the same manner as the spark created by rubbing a piece of plastic against woollen cloth.

A second species of mechanically generated noise is piezoelectricity in the dielectric. Although more\ common in cheap cables, one should be aware of it.

Mechanical deformation of the dielectric causes electrical potentials to be generated.

Both species of mechanically generated noise can be reduced or eliminated by proper mounting of the cable. Although rarely a problem at lower frequencies, such noise can be significant at microwave
frequencies when signals are low.


What is Voltage standing wave ratio (VSWR)?
Voltage standing wave ratio (VSWR) Defined.

When an RF cable is mismatched, i.e. connected to a load of a different impedance to that of the cable, not all the power supplied to the cable is absorbed by the load. That which does not enter the load is reflected back down the cable.

This reflected power adds to the incident voltage when they are in phase with each other and subtracts from the incident voltage when the two are out of phase. The result is a series of voltage – and current – maxima and minima at halfwavelength intervals along the length of the line.

The maxima are referred to as antinodes and the minima as nodes. The voltage standing wave ratio is the numerical ratio of the maximum voltage on the line to the minimum voltage: VSWR = Vmax/Vmin.

It is also given by: VSWR = RL/Z0 or Z0/RL (depending on which is the larger so that the ratio is always greater than unity) where RL = the load resistance.

The return loss is the power ratio, in dB, between the incident (forward) power and the reflected (reverse) power. The reflection coefficient is the numerical ratio of the reflected voltage to the incident voltage.

The VSWR is 1, and there is no reflected power, whenever the load is purely resistive and its value equals the characteristic impedance of the line. When the load resistance does not equal the line impedance, or the load is reactive, the VSWR rises above unity.

A low VSWR is vital to avoid loss of radiated power, heating of the line due to high power loss, breakdown of the line caused by high voltage stress, and excessive radiation from the line. In practice, a VSWR of 1.5:1 is considered acceptable for an antenna system, higher ratios indicating a possible defect.


What is Doppler Effect?
Doppler Effect Defined.

Doppler effect is an apparent shift of the transmitted frequency which occurs when either the receiver or transmitter is moving. It becomes significant in mobile radio applications towards the higher end of the UHF band and on digitally modulated systems.

When a mobile receiver travels directly towards the transmitter each successive cycle of the wave has less distance to travel before reaching the receiving antenna and, effectively, the received frequency is raised.

If the mobile travels away from the transmitter, each successive cycle has a greater distance to travel and the frequency is lowered. The variation in frequency depends on the frequency of the wave, its propagation velocity and the velocity of the vehicle containing the receiver.

In the situation where the velocity of the vehicle is small compared with the velocity of light, the frequency shift when moving directly towards, or away from, the transmitter is given to sufficient accuracy for most purposes by:

fd = (V/C )ft

fd = frequency shift, Hz
ft = transmitted frequency, Hz
V = velocity of vehicle, m/s
C = velocity of light, m/s

Examples are:
• 100 km/hr at 450 MHz, frequency shift = 41.6Hz
• 100 km/hr at 1.8 GHz – personal communication network (PCN)
frequencies – frequency shift = 166.5Hz
• Train at 250 km/hr at 900MHz – a requirement for the GSM pan-
European radio-telephone – frequency shift = 208 Hz

When the vehicle is travelling at an angle to the transmitter the frequency shift is reduced. It is calculated as above and the result multiplied by the cosine of the angle of travel from the direct approach.


What are the Memory IC Failure Modes?
Memory IC Failure Modes Defined.

Memory ICs failures result in the inability to read or write data, erroneous data storage, unacceptable output levels, and slow access time. The specific failures that cause these problems are as follows:

Open and short circuits: can cause various problems from a single bit error to a catastrophic failure of the whole device.

Open decoder circuits: cause addressing problems to the memory.

Multiple writes: writing one cell actually writes to that cell and other cells (multiple write and address uniqueness problems).

Pattern sensitivity: the contents of a cell become complemented due to read and write operations in electrically adjacent cells (cell disturbances, adjacent cell disturbances, column disturbances, adjacent column disturbances, row disturbance, adjacent row disturbance).

Write recovery: the access time of the device may be slower than specified when each read cycle is preceded by a write cycle, or a number of write cycles.

Address decoder switching time: this time can vary depending on the state of the address decoder prior to switching and on the state to which the decoder is switching.

Sense amplifier sensitivity: memory information may be incorrect after reading a long series of similar data bits followed by a single transition of the opposite data value.

Sleeping sickness: the memory loses information in less than the specified hold time (for DRAMs).

Refresh problems (may be static or dynamic): the static refresh test checks the data contents after the device has been inactive during a refresh. In dynamic refresh, the device remains active and some cells are refreshed. All cells are then tested to check whether the data in the nonrefreshed cells is still correct.

Special tests are needed for memory devices to insure the integrity of every memory bit location. These functional tests are composed of four basic tests, pattern tests, background tests, timing test, and voltage level tests.

Memory tests cannot be specified to test each part 100% as a RAM can contain any one of 2N different data patterns and can be addressed in N factorial (N!) address sequences without using the same address twice.

Test times shown may be extremely long for some high-density memory devices; a GALPAT test for a 4 M DRAM would take 106 days to execute. It is easy to see how impractical it is to overspecify device testing. Any test plan should be developed along with the supplier of the memory devices you are to purchase.

System level tests may use bit-map graphics where the status of the memory cells is displayed on the cathode ray tube (CRT) display of the system (i.e., failing bits show up as a wrong color). Various patterns are read into the memory and the CRT may be configured to show 1 cell equivalent to one pixel (a picture element) or compressed to show 4, 16, or 64 cells per pixel depending on the number of pixels available and the memory size.

Zoom features can be used to scale the display for close examination of failing areas of the memory. Note, in large memory intensive systems, consider using error correction codes to correct hard (permanent failure) and soft errors (i.e., alpha particle upsets, a single upset that does not occur again).

One vendor of video RAMs estimates a soft error rate of a 1 Meg part of 3.9 FITs (at a 500-ns cycle time with Vcc at 4.5 V, and a 4 Meg DRAM error rate of 41 FITs (at a 90% confidence level, 5 Vcc operation with 15.625-μs cycle (refresh) rate). Soft error rates are dependent on cycle time and operating voltage; the lower the voltage and faster the cycle time, the higher the failure in time rate.

One thousand FITs equals 1 PPM (1 failure in 106 h), which equals 0.1%/1000 (0.1% failures every 1000 h). When calculating soft error rates, add the refresh mode rate and the active mode rate, which can be determined from acceleration curves provided by the manufacturer.


What is Rayleigh Scattering?
Rayleigh Scattering Explained.

As a light pulse traverses the optical fiber, a small percentage of the light is scattered in all directions by the collision of photons with the materials that make-up the transmission medium, at the molecular level.

This phenomenon is called Rayleigh scattering. Rayleigh scattering is the primary source of power loss in optical fiber, accounting for well over 95% of the total light lost, extrinsic factors aside. In simple terms, as light propagates in the core of the optical fiber it interacts with the atoms in the glass structure in a complex manner depending upon the energy of the light (i.e., wavelength) and the size of the particles in the specific material or materials used in the waveguide.

Under certain conditions, photons may elastically collide with the atoms in the fiber matrix and be scattered as a result. Attenuation occurs when light is scattered at an angle that does not support continued propagation in the desired direction.

The lost light is either diverted out of the core or reflected back to the transmitter source. Less than 1% of the scattered light is reflected back, or “backscattered,” toward the transmitter source, and it is this effect that forms the basis by which optical time domain reflectometers (OTDR) operate.

The OTDR is an important tool in fiber optics and is the piece of equipment most commonly used for testing and troubleshooting fiber optic systems. A characteristic OTDR trace is provided below.

Because the reflected light comes from the light pulse the original pulse power decreases, adding to the total attenuation before it reaches the receiver. The slope of the OTDR trace represents the attenuation coefficient of the fiber for the particular wavelength of light being transmitted.

The trace appears essentially straight, barring isolated events, because the overall attenuation coefficient of the fiber, which includes the Rayleigh backscatter coefficient, is assumed to be constant.


What are the Benefits of Optical Fiber Telecommunications Systems?
Advantages of Optical Fiber Telecommunications System.

Optical fiber provides many fundamental advantages over alternative transmission technologies for telecommunications applications. The comparatively limited performance of copper conductor based systems forces the use of expensive signal conditioning and regeneration equipment (e.g., amplifiers and repeaters) at much closer intervals than for fiber optic systems. 

A single line of a voice grade copper system (i.e., 56 kbs) longer than a couple of kilometers requires the use of in-line signal processing for satisfactory performance, and even then is subject to the electromagnetic effects of interfering radio frequency sources such as radio, television, cell phone, and air traffic control broadcasts.

As information throughput requirements increasewith the demands ofmore data-intensive applications at the end-user premises, the spacing between the copper-based repeater points must decrease in order to maintain the same aggregate data rate capability over a given length. 

Contrast that to all-optical systems in which it is not unusual to transmit 10 gigabits per second data rates over hundreds of kilometers without the need for active signal processing between the transmitter and receiver.

Additionally, as it becomes necessary to increase the data transmission capacity or coverage area of a telecomunications system, the diameter and weight of cables for copper conductor systems increase much more rapidly than for optical fiber systems, resulting in a proportionally higher increase in materials, installation, and maintenance related costs.

The small size of optical cables, coupled with readily available components that make efficient use of the optical fiber’s transmission capabilities, enable them to be manufactured and installed in much longer lengths than copper cables. The virtually unlimited capacity of optical fiber also alleviates fears of incurring significant long-termcosts associated with frequent system upgrades, extensions, or over builds.

The availability of long lengths of individual lightweight fiber optic cables, up to 10 km or more, also make the installation of fiber optic systems much safer, easier, and less expensive, than comparable copper-based systems. Because of their design, fiber optic cables can generally be installed with the same equipment historically used to install twisted pair and coaxial cables, allowing some consideration for the smaller size and lower standard tensile strength properties of fiber optic cable.

More importantly, fiber optic cable design has progressed to the point where it serves as an enabling technology for newer installation methods that are faster, less expensive, and less intrusive to the environment than traditional installation means. 

Optical cables can be installed in duct system spans of 4000 meters (m) or more depending on the condition, construction, and layout of the duct system, and the details of the installation technique(s) used. Even longer lengths of fiber optic cable can be installed aerially, trenched, or buried in the ground and ocean floor. 

These extra-long lengths of cable reduce the number of splice points, thereby making the overall installation of optical fiber based telecommunications systems more efficient. The small size of fiber optic cable also saves on valuable conduit space in buried duct applications. 

This feature becomes even more prevalent when considering some emerging cable types that are specifically designed for use with air-blown or air-assist installation techniques into miniature ducts that are only about one centimeter in diameter.

Another advantage of optical fiber and fiber optic cable is the inherent flexibility in design options, allowing for the development of innovative products for specific applications. Since optical fiber is a man-made composite glass structure, it can be custom designed to meet optimal cost/performance targets in any number of specific applications. 

As it does not conduct electrical current and is not affected by electromagnetic interference, fiber optic cable can be made all dielectric, making it the ultimate in electromagnetically compatible transmission media. 

This eliminates such issues as dangerous ground loops, the effects of voltage spikes from the cycling of heavy electrical equipment, and requirements for separate conduits for metallic conductors. It also improves the security of controlled transmission rooms as it is much more difficult to tap a fiber optic line, andmuch easier to provide security for fiber optic cable.



Radar is an acronym for radio detection and ranging as these were primary functions during the early use of radar. Radars can also measure other target properties such as range rate (Doppler), angular location, amplitude statistics, and polarization scattering matrix.

In its simplest form, a radar propagates a pulse from an antenna to a target. The target reflects the pulse in many directions with some of the energy back scattered toward the radar. The radar return is received by the radar and subjected to processing to allow its detection.

Since the pulse travels at approximately the speed of light, the distance to the target can be determined based on the round trip time delay. Reflections from undesired targets are known as clutter and often include terrain, rain, man-made objects, etc.

Usually, the radar will have a narrow beam so that the angular location of the target (i.e., azimuth and elevation) can also be determined by some technique such as locating the centroid of the target returns as the beam scans across the target or by comparing the signals received simultaneously or sequentially by different antenna patterns or overlapped beams.

The radial velocity of the target can be determined by differencing the range measurements. Since the range measurements may not be very accurate, better range rate accuracy can be obtained by coherently measuring the Doppler frequency; that is, phase change from pulse-to-pulse in a given range cell.

At microwave frequencies, the wavelength is quite small and, hence, small changes in range are readily detected. Generally, frequency is measured by using a pulse Doppler filter bank, pulse pair processing, or a CW frequency discriminator.

Coherently measuring the frequency is also a good way for filtering moving targets from stationary or slowly moving clutter. Radar parameters vary with the type of radar. Typically, the radar transmitted pulse width is 1 to 100 μs with a pulse repetition frequency (prf) of 200 Hz –10 KHz.

If the antenna is a mechanically rotated reflector, it generally rotates 360◦ in azimuth at about 12–15 r/min. If the two-way time delay is T, the range to the target is R = 0.5T × c, where c = 3 × 108 m/s is the velocity of light.


How to Classify Channel and Station In AM?

In standard broadcast (AM), stations in the U.S. are classified by the FCC according to their operating power, protection from interference, and hours of operation. A Class A station operates with 10–50 kW of power servicing a large area with primary, secondary, and intermittent coverage and is protected from interference both day and night.

These stations are called clear channel stations because the channel is cleared of nighttime interference over a major portion of the country. Class B stations operate full time with transmitter powers of 0.25–50 kW and are designed to render primary service only over a principal center of population and contiguous rural area.

Whereas nearly all Class A stations operate with 50 kW, most Class B stations must restrict their power to 5 kW or less to avoid interfering with other stations.

Class B stations operating in the 1605–1705 kHz band are restricted to a power level of 10 kW daytime and 1 kW nighttime. Class C stations operate on six designated channels (1230, 1240, 1340, 1400, 1450, and 1490) with a maximum power of 1 kW or less full time and render primarily local service to smaller communities.

Class D stations operate on Class A or B frequencies with Class B transmitter powers during daytime, but nighttime operation, if permitted at all, must be at low power (less than 0.25 kW) with no protection from interference.

Although Class A stations cover large areas at night (approximately a 1000 km radius), the nighttime coverage of Class B, C, and D stations is limited by interference fromother stations, electrical devices, and atmospheric conditions to a relatively small area.

Class C stations, for example, have an interference-free nighttime coverage radius of approximately 8–16 km. As a result there may be large differences in the area that the station covers daytime vs. nighttime. With over 4900 AM stations licensed for operation by the FCC, interference, both day and night, is a factor that significantly limits the service stations may provide.

In the absence of interference, a daytime signal strength of 2 mV/m is required for reception in populated towns and cities, whereas a signal of 0.5 mV/m is generally acceptable in rural areas without large amounts of man made interference.

Secondary nighttime service is provided in areas receiving a 0.5-mV/m signal 50% or more of the time without objectionable interference. Table 16.1 indicates the interference contour overlap limits. However, it should be noted that these limits apply to new stations and modifications to existing stations.

Nearly every station on the air was allocated prior to the implementation of these rules with interference criteria that were less restrictive.

Note: SC = same channel; AC = adjacent channel; SW = skywave; GW = groundwave; RSS = root of sum squares. When a station is already limited by interference from other stations to a contour of higher value than that normally protected for its class, this higher-value contour shall be the stablished protection standard for such station. Changes proposed by Class A and B stations shall be required to comply with the following restrictions.

Those interferers that contribute to another station’s RSS using the 50% exclusion method are required to reduce their contribution to that RSS by 10%. Those lesser interferers that contribute to a station’s RSS using the 25% exclusionmethod but do not contribute to that station’s RSS using the 50% exclusion method may make changes not to exceed their present contribution.

Interferers not included in a station’s RSS using the 25% exclusion method are permitted to increase radiation as long as the 25% exclusion threshold is not equaled or exceeded. In no case will a reduction be required that would result in a contributing value that is below the pertinent value specified in the table.

cSkywave field strength for 10% or more of the time. For Alaska, Class SC is limited to 5 μV/m.
dDuring nighttime hours, Class C stations in the contiguous 48 states may treat all Class B stations assigned to 1230, 1240, 1340, 1400, 1450, and 1490 kHz in Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands as if they were class C stations.

Source: FCC Rules and Regulations, revised 1991; vol. III, pt. 73.182(a).


What is half-wave dipole antenna?

Most antennas can be analysed by considering them to be transmission lines whose configurations and physical dimensions have been altered to present easy energy transfer from transmission line to free space. In order to do this effectively, most antennas have physical sizes comparable to their operational wavelengths.

Figure 1.12(a) shows a two wire transmission line, open-circuited at one end and driven by a sinusoidal r.f. generator. Electromagnetic waves will propagate along the line until it reaches the open-circuit end of the line.

At the open-circuit end of the line, the wave will be reflected and travel back towards the sending end. The forward wave and the reflected wave then combine to form a voltage standing wave pattern on the line. The voltage is a maximum at the open end. At a distance of one quarter wavelength from the end, the voltage standing wave is at a minimum because the sending wave and the reflected wave oppose each other.

Suppose now that the wires are folded out from the λ/4 points, as in Figure 1.12(b). The resulting arrangement is called a half-wave dipole antenna. Earlier we said that the electromagnetic fields around the parallel conductors overlap and cancel outside the line.

However, the electromagnetic fields along the two (λ/4) arms of the dipole are now no longer parallel. Hence there is no cancellation of the fields. In fact, the two arms of the dipole now act in series and are additive.

They therefore reinforce each other. Near to the dipole the distribution of fields is complicated but at a distance of more than a few wavelengths electric and magnetic fields emerge in phase and at right angles to each other which propagate as an electromagnetic wave.

Besides being an effective radiator, the dipole antenna is widely used as a VHF and TV receiving antenna. It has a polar diagram which resembles a figure of eight. Maximum sensitivity occurs for a signal arriving broadside on to the antenna. In this direction the ‘gain’ of a dipole is 1.5 times that of an isotropic antenna.

An isotropic antenna is a theoretical antenna that radiates or receives signals uniformly in all directions. The gain is a minimum for signals arriving in the ‘end-fire’ direction. Gain decreases by 3 dB from its maximum value when the received signal is ±39° off the broadside direction.

The maximum gain is therefore 1.5 and the half-power beam-width is 78°. The input impedance of a half-wave dipole antenna is about 72 Ω. It turns out that the input impedance and the radiation resistance of a dipole antenna are about the same.


The highly anticipated The Witcher 3 on XBOX.

Ho! What news from the PAX East panel? Oi, what did you call me? Well, during CD Projekt Red’s panel it showed off a juicy seven-minute gameplay demo in which Geralt takes to the sprawling No Man’s Land to dispatch a phantom harassing a trade route.

This phantom, it turns out, is a Royal Wyvern, which gets its scaly ass kicked by fire spells, crossbow bolts and swordplay.

What’s all this talk of ice skating, then?
The strangest moment came when senior game designer Damien Monnier revealed a feature sadly cut. “At some point we had the idea of ice-skating,” he said. “You were going to skate and fight, and you could slice heads and the blood goes on the ice and it’s beautiful.”

Apparently you could even control Geralt’s legs with the left and right triggers. Any details on the world? Wild Hunt’s world simulates things even when you’re not around to witness them. Monsters, for example, spawn miles away from you. If you kill an animal, the scent might draw roaming monsters.

If two monsters go for the same kill there’s a chance they could clash, regardless of your involvement. The engine can calculate random NPC dust-ups, too.

What other cool things are there to do? CD Projekt Red confirmed rich customisation options for the UI, where you can enable and disable elements according to how much you like meters and bars and stuff. And bad news for you Annie Leibovitz types, because there’s no built-in photo mode. But we won’t bemoan that too much thanks to Xbox One’s new screenshot functionality.

Enough! Tell me when it’s out immediately. There’s not long to wait now, you lucky thing. After two high-profile delays in which CDP released a shoe-gazing apologetic statement, it’s finally announced the official release date: 19 May– so close you can almost taste the Griffin sweat.

Actually don’t do that. Yes, it’s almost a year late, but we’re willing to forgive this epic-looking RPG.



Typical digital clocks using clock chips MM5387/MM5402 and MM5369 show normal time in only
hours and minutes, and seconds or alarm time is visible only after pressing a pusht o on switch. Here’s a digital clock using the same IC (MM5387) that shows normal time in hours, minutes, and seconds and alarm time simultaneously. For this, ten 7-segment LED displays and a few extra ICs and some discrete components are needed.

IC1, IC5 - CD4017BE decade counter/
IC2 - NE555 timer
IC3 - MM5387 clock chip
IC4 - CD4060 14-stage binary
T1-T5 - BC547 npn transistor
D1-D6 - 1N4001 rectifier diode
D7, D8 - 1N4148 fast switching diode
Resistors (all ¼-watt, ±5% carbon,
unless stated otherwise):
R1 - 10-kilo-ohm
R2 - 150-ohm
R3-R7 - 15-kilo-ohm
R8 - 3.3-mega-ohm
C1 - 0 .01μF ceramic disk
C2 - 4.7μF, 16V electrolytic
C3 - 1000μF, 16V electrolytic
C4 - 470μF, 16V electrolytic
C5-C7 - 0.22μF ceramic disk
C8, C9 - 47pF ceramic disk
XTAL - 4.9152MHz crystal
LED1, LED2 - 5mm dia. red LED
DIS1-DIS10 - LT543 common-cathode
7-segment display
S1 - SPDT switch
S2-S7 - Push-to-on tactile switch
X - 230V AC primary to 4.5V-0-
4.5V secondary, 500mA
- 9V PP3 battery



LG EG9900 4k TV

Curved TVs are hotter than Oman in summer right now, but while they’re perfect for watching two-abreast, when there’s a room full of people, those in the middle can’t see diddly. Lg’s revolutionary bendable screen could solve that irksome problem by adapting to your needs with its flexible display.

Instead of pigeon-holing you with either flat or curved, Lg’s bendable tV can, rather brilliantly, do both. When it’s just you and a friend, go curved for maximum immersion.

When you’ve got friends around, a wave of the tV’s remote will make the display instantly flex into a flat position, so everyone gets a slice of the action.

LG is really pushing the organic technology found inside its panels, and the Eg9900 features the same oLEd spec, giving this screen impeccably bright and vibrant colours and perfect blacks. With ‘just’ a 4K resolution to contend with, you can lap up all that glorious 4K content rearing its head right now.

Yes, its 77-inch screen is a little bit gargantuan, but the cool, bendable technology will eventually trickle down to the smaller models, so you won’t necessarily have to build a man cave to justify your rather ott purchase, though you should.

TOP 6 Miniature Gadgets To Boost Your Portable Computing Power in 2015

The ThinkPad STACk adds layers
of productivity to your laptop. The units
– a 2x2 watt speaker, 1TB portable uSB 3.0
hard drive, dual uSB power bank, and a
Wi-Fi access point – hold together
magnetically, with a 136x76mm footprint.
$377 LenoVo.CoM ouT APRIL

Plug Intel’s Windows 8.1 Compute Stick
into the HDMI port of your TV or monitor
and you’ve got an Atom-powered PC with
2GB RAM, and 32GB storage, controlled
via Bluetooth keyboard and mouse. A Linux
version will also be released.
$149 InTeL.CoM ouT SPRInG

Seagate claims to offer the world’s
thinnest 500GB portable hard drive – just
7mm thick and 122.5mm long. The Sevenmm
connects and powers via a braided uSB
3.0 cable and has a reassuringly utilitarian
design, inspired by the ‘bare drive’ look.
£149 ouT noW

4. AMpliCiTY
Amplicity is similar to an Intel nuC. The
difference is that instead of buying it, you
rent it at $99 for six months. With 4GB
RAM, 128GB storage plus 1TB cloud space,
it comes with office and Creative Cloud,
and is a bit bigger than a smartphone.

zutALabs has torn the print head out of a
conventional printer, robotised it in a neat
teardrop design, and is now selling it as a
pocket printer. Put your paper down on a
flat surface, place zutA top left, send it the
file, and – bzzzt-bzzzt-bzzzzt – page ready.

6. pRYNT
You could copy your pics from your phone
to your computer and print them, or go to
a website to do it for you. But a Prynt case
for your smartphone has a printer built in,
including 10 sheets of paper, meaning you
can snap and print on the spot.


Here is an inexpensive electronic car security system with remote control that uses readily available, low-cost components. The gadget comprises a base unit, which remains fitted inside the vehicle, and a remote control handset for activating/deactivating the base unit. The base unit, in enabled state, can be used to set off an alarm device when an unauthorised person tries to gain access to the vehicle.

Remote control handset

The remote control handset is used to switch on/off the base unit installed inside the vehicle.

Base Unit


The small-signal amplifier is generally referred to as a voltage amplifier because it usually converts a small input voltage into a much larger output voltage. The audio power amplifier works on the basic
principle of converting low-power audio signal to a suitable level to be delivered to the load.

This low-power amplifier circuit is useful for the amplification of sound from small-signal devices such as mobile phones, laptops or desktops.

Circuit and working As shown in Fig. 1, this circuit is built around a step-down transformer (X1), bridge rectifier BR1, regulators 7809 (IC1) and 7909 (IC2), dual op-amp TL072 (IC3), low-power amplifier LM386 (IC4) and some other components.

The circuit can be divided into two sections—dual power supply section and amplifier section. The dual power supply section is built around step-down transformer X1 (230V ac primary to 12V-0-12V, 1A secondary) and two voltage regulators 7809 and 7909.

IC 7809 is a positive voltage regulator, while 7909 is a negative voltage regulator. Diodes D1 and D2 are used to protect IC1 and IC2 against reverse voltages from capacitors connected to the regulators. These regulators provide ±9V regulated output for the operation of the circuit.

Use suitable heat sinks with the regulator ICs because they get hot during operation. In case of overheating, there is provision for a thermal shutdown.

The amplifier section is built around TL072 (IC3) and a low-power amplifier LM386. The op-amp A1 of IC3 operates as a low-noise preamplifier. Capacitor C8 is used in order to pass low frequency. The op-amp A2 of IC3 operates as a low-pass filter. For changing the cut-off frequency, you have to change the values of capacitors C11 and C12.

LM386 is a low-power amplifier IC with built-in biasing and inputs that are referred to the ground. It has a gain of 20 and can drive a speaker of 8-ohm impedance.

Parts List
IC1 - 7809, +9V regulator
IC2 - 7909, -9V regulator
IC3 - TL072 dual op-amp
IC4 - LM386 low power audio
BR1 - 1A bridge rectifier
D1, D2 - 1N4007 rectifier diode
Resistors (all 1/4-watt, ±5% carbon):
R1 - 1-kilo-ohm
R2 - 10-kilo-ohm
R3 - 2.2-kilo-ohm
R4 - 47-kilo-ohm
R5-R7 - 33-kilo-ohm
R8 - 56-kilo-ohm
R9 - 3.3-ohm
VR1 - 10-kilo-ohm potentiometer
C1, C3 - 1000μF, 35V electrolytic
C2, C4 - 0.33μF ceramic disk
C5, C6 - 1μF, 25V electrolytic
C7, C14 - 220μF, 25V electrolytic
C8 - 4.7μF, 25V electrolytic
C9, C10, C13 - 0.1μF ceramic disk
C11, C12 - 0.01μF ceramic disk
LS1 - 8-ohm, 0.5W speaker
RCA1 - RCA socket
X1 - 230V AC primary to
12V-0-12V, 1A secondary
- 8-pin IC bases for ICs
- Heat sinks for regulators


Astronauts need 3D printers, despite their not-so-luxurious lifestyles. You must be wondering about the need of a 3D printer in an astronaut’s life.

Well, there is a relevant answer too. Stuff breaks in space and replacement of the same is not an easy task while someone is in the space.

So, to help those folks, Made in Space has designed a 3D printer that sidesteps Earth’s gravity, when it is used in the orbit. The 3D printer, known as the Zero-G printer, is not made of molten filament but its surface tension holds a widget.

There are plans to make a gizmo that would allow astronauts to melt tools. Made in Space has focused on cost-effective measures.

The team is also planning 3Dprinting robots, which will be sent to Mars or the Moon. Several tests have been performed on parabolic plane flights by Made in Space that says 15 to 20 minutes are required for complete parts to be printed.

The printer has been designed to be operated from the ground, most of the time.


Schematic diagram for rain alarm.


Water is a conductor of electricity. When water is in contact with the probe then there is a flow of current which reaches to the base of Q1. Transistor Q1 is a NPN transistor which conducts. With the conduction of Q1 electron reaches to Q2 which s a PNP transistor .

Q2 also conducts and current flows through the speaker. In aspeaker there is inductive coil which causes motion in one direction and also produce induce current which is in opposite direction to the flow of current this induce current in the form of pulse flows through a capacitor, resistance and switches off Q1 and relax .

This process repeats again and again till probe is in contact with water or we can say there is a oscillation in the circuit thus speaker diaphragm vibrates and gives a tone. Frequency of the circuit depends on the value of Speaker Coil impendance, Capacitor and Resistance Value.


Each electromagnetic field can be divided into four zones: the near zone, the intermediate zone, the far zone, and the plane-wave zone. The near zone is the portion of the field close to the source. It is defined as the region where stored energy is much greater than any radiating energy. The far zone is the region where:

1) the stored field energy is much less than the radiating energy,

2) the wave impedance is approximately ho = 120p, and 3) the electric and magnetic fields are perpendicular to one another.

The intermediate zone is the region between the near and far zones. The plane-wave zone is the region in the far zone where the radiation can be approximated as plane waves.

This last zone is different from the others because its definition depends on the size of the receiving antenna.

Just as a basketball’s surface appears curved to a human but relatively flat to a tiny microorganism on the surface, and the Earth’s surface appears flat to a walking human, the apparent flatness of a curved wavefront depends on the relative size of the observer.

In optics, the plane-wave zone is called the Fraunhofer zone, and the combination of the three other zones is called the Fresnel zone.


SOLDERING IRON - Basic tools for electronic projects.

The connecting lead of each component must be soldered into place on the printed circuit board. A specialized soldering iron must be used — one that is neither too big nor too powerful to harm either the component or the circuit board.


This is a simple electronic project of automatic shutoff battery charger. Adjust this circuit by setting the 500-ohm resistor while it is attached to a fully charged battery.

The circuit is capable of charging a 12-v battery up to six ampere rate.


This is a simple schematic diagram of automatic water pump controller.

The circuit of a water pump controller, as shown in the diagrag, comprises three npn transistors, all connected as emitter followers to present high input and low output impedance. Gate N1 of the quad NAND gate iC is connected as an inverter, while two other NAND gates N2 and N4 form a set-reset flip-flop controlled by outputs of NAND gate N1 and pole voltage of relay Rl2.

The tank has a reference probe C, which is directly connected to 12V supply, while probe a represents the lower limit of liquid (any conductive liquid including normal drinking water) level. if liquid level falls below this level the pump motor must start and remain on until the liquid touches the upper probe B.

When the liquid level falls below probe a level, transistor T1 is cut off and hence pin 13 of gate N4 (via N/C contact of relay Rl2) is at ground level. The output pin 11 of gate a therefore goes high.

Transistor T3 conducts to energise relay Rl1 and the pump motor is switched on through its contacts. Once water touches probe A (but not the upper limit probe B), relay RL2 energises because of forward biasing of transistor T1, whereby pin 13 of gate N4 goes high.

But its other input pin 12 is low as transistor T2 is not conducting. hence input to gate N1 is low and the logic output of gate N2 is low.

PartS LiSt
IC1 - CD4011 - quad 2-input NAND gate
T1- T3 - BC547 - npn transistor
D1, D2 - 1N4001 - rectifier diode
R1, R2, R6 - 1-kilo-ohm - resistor, 0.25W
R3, R5 - 47-kilo-ohm - resistor, 0.25W
R4 - 10-kilo-ohm - resistor, 0.25W
Rl1, Rl2 - 12V, 1 C/O - relay with 1a contact rating
- probes - 3 metal probes on insulating rod
- 12 V battery



A breadboard is used for making solderless temporary connections using leads, which are pushed into the holes in the board to make connections.

This is basically a way of wiring a circuit temporarily, for testing purposes or to try out an idea. Since no soldering is done, all the components can be reused afterwards. it is easy to change connections and replace components.

Below is the external appearance of a breadboard. it has two rows of supply/ground channels on the
top and bottom, separated by two 5-hole vertical channel rows.

The conductor channels embedded under the holes if you rip open the breadboard from the bottom, you can easily see these conducting channels. all adjacent holes are separated by 2.54 mm (0.1 inch), enabling direct insertion of most iCs that have identical pin-to-pin spacing.

Normally, two sections of the breadboard are integrated into a single unit and are sold as a single breadboard.