Electromagnetic Radiation and Human Health
Reduce exposure to potentially harmful electromagnetic fields. AlphaLab's handheld TriFieW Meter measures AC electric fields, AC magnetic fieids and radio microwave power density. Find ground faults, AC current wires or measure high-field generators with the Magnetic setting - 100 milligauss, 60 Hz) identify poorly grounded or shielded equipment, high VDT or fluorescent light lieids, distinguish hot vs. ground wires with Electric setting (.5 - 100 hV m, 60 Hz) measure antenna radiation patterns, leaky microwave ovens, etc. on RF microwave setting (50 MHz to 3 GHz, ,01 to 1 mW cm2). AfphaLab, T20O South 300 West, Salt Lake Cityp UT 64101. Call 800-769-3754 OR 801 487-9492 lor speedier service or free literature on electromagnetic radiation health risks.
Reduce exposure to potentially harmful electromagnetic fields. AlphaLab's handheld TriField Meter measures AC electric fields, AC magnetic fields and radio microwave power density. Find ground faults, AC current wires or measure high-field generators with the Magnetic setting (+2 - 100 milligauss. 60 Hz) identify poorly grounded or shielded equipment, high VOT or fluorescent light fieJds, distinguish hoi vs. ground wires with Electric setting (.5 - 100 kV m, 60 Hz) measure antenna radiation patterns, leaky microwave ovens, etc. on RF microwave setting (50 MHz lo 3 GHzT .01 to 1 mW cm2). AlphaLab, 1272 Alameda Ave, Salt Lake City, UT 84102 Call (801 532-6604 lor speedier service or free literature on electromagnetic radiation health risks.
Reduce exposure to potentially harmful electromagnetic fields. AtptiaLab's handheld TriFIeld Meter measures AC electric fields* AC magnelic fields and radio-microwave power density. Find ground faults. AC current wires or measure high-field generators with the Magnetic setting (.2 - 100 mtlligau Ep GO Hz) identify poorly grounded or shielded equipment, high VDT or fluorescent light fieFds, distinguish hot vs. ground wires with Electric setting (.5 - 100 kV m, 60 Hz) measure antenna radiation patterns, leaky microwave ovens, etc. on RF microwave setting (50 MhU to 3 GHz, .01 to 1 mW cm*). AlphaLab, 1260 South 300 West. Salt Lake City, UT 84101 . Call 80Q-769-37SJ OR 801-487-9492 for speeder service or free titerauire on electromagnetic radiation health risks.
It was considered important that System 35 meet new standards for electromagnetic interference. We had seen real needs in several applications. Government regulations were being enforced more rigidly and were becoming more severe. European users in particular demanded it. As a result, System 35's radiated interference levels are approximately 20 dB lower than those of its predecessors, enabling it to meet the standard of VDE radiated interference level A (see article, page 16).
AlphaLab, 1272 Alameda Ave, Salt Lake City, UT 64102 Call (301) 532-6604 for speedier service or free literature on electromagnetic radiation health risks. Reduce exposure to potentially harmful electromagnetic fields, AJphaLab's handheld TriField Meter measures AC electric fields, AC magnetic fields and radio microwave power density. Find ground faults, AC current wires or measure high-field generators with the Magnetic setting (,2 - 100 milligauss, 60 Hz) identify poorly grounded or shielded equipment high VDT or fluorescent light fields, distinguish hot vs. ground wires with Electric setting (,5 - 100 kV mf 60 Hz) measure antenna radiation patterns, leaky microwave ovens, etc. on RF microwave setting 50 MHz to 3 GHz, .01 to 1 mW cm2). AlphaLab, 1272 Alameda Ave, Salt Lake City, UT 64102 Call (301) 532-6604 for speedier service or free literature on electromagnetic radiation health risks.
Are you womed about electromagnetic radiation. TV cmi distribution loss poor antenna performance, or EMf RFI7 The DtGl-FIELD field strength meter w -1 pul you ai ease. With nsirequency response oi DC up to T2 GHZ rt reaenry oeleos potermal jioctromagne c rad a-tion hazaras h is an eiceJlent ooi tor measurtng TV coax distribution loss, tr addytkxl OGt-FltJ car easjly find 60-Hz AC-r ne inte ferenoe asw tlas Rfl EWI Inst-vmertaDor isojpt-mg Mt-ups. Se trvity 100 MMz Mode 'A' i5C n ro Watts ModerB'S rwio wans
Transmission of intelligence through space by means of electromagnetic radiation cannot be accomplished satisfactorily at audio frequencies. There are several reasons for this (1) The radiation efficiency of antennas is very low at audio frequencies, and so the range is small. (2) Efficient radiation and reception of electromagnetic waves require the use of antennas and circuits tuned to the frequencies of the waves. The antennas required at audio frequencies would be impractical because of their great lengths, and they would not respond equally well to all frequencies in the audio range. (3) If transmission were effected at audio frequencies, all transmitters would operate over the same frequency range and so the programs of various transmitters would be heard simultaneously at the receiver. These difficulties are avoided by radiating a radio-frequency wave, the amplitude, frequency, or phase of which is varied in accordance with the audio-frequency signals that it is desired to...
They went on to more important things. Thousands of years later, I, a radio amateur, sat at my desk in Dallas and communicated with a fellow named Peter in Pitea, Sweden. After a brief exchange of electromagnetic fields at the speed of light, I was possessed of the information that my signal had indeed reached Sweden in fairly readable form. He was little better informed than L We did not go on to more important things. It was a contest of course. Admittedly, but for the contest, he probably wouldn't have been on the air. But still Zip Forty-five seconds What result 5-7, name is Peter 5-8, name is Don.
In general, echocardiography has made an important contribution to patient care because it is noninvasive (nothing need be injected into the body , it can be done without hospitalizing the patient (and so the cost is kept downj, there is no ionizing radiation involved, and there is no known risk to the patient from performing the procedure. It offers improved differentiation of soft tissues which look the same in X-ray images and because of all of the above, it is quite repeatabie, The repeatability translates to the ability to follow patients and learn the natural history of their condition with and without interventions to change that natural history. If the physician simply wants to make a diagnosis of a suspected condition, the physician mighl often use echocardiography now, whereas a cardiac catheterization, with attendant risk and cost, would have been the method of choice in the past. Certainly the echocardiogram is superior to any other technique for the diagnosis of small...
To decrease emission of electromagnetic energy and sus-ceptibil itv to it. the logic ground is isolated from the frame ground. This is achieved by electrically isolating all printed circuit boards and backplanes from the sheet-metal cardcages. Radiated emissions are minimized by providing and connecting ground planes in the printed circuit boards
Rotational microwave spectrometers detect and record the absorption spectra of low-pressure gases or vapors at microwave frequencies. A spectrum recorded by one of these instruments is a graphic plot of the electromagnetic energy absorbed by the sample as a function of the frequency of the energy. The processes which lead to the absorption of radiation by the sample are governed by quantum-mechanical laws, and as a consequence a given substance will absorb energy only at discrete frequencies. A typical spectrum, therefore, consists of many very narrow peaks called absorption lines.
When a nuclear bomb is detonated, electromagnetic energy is released across the entire spectrum, from extremely low frequency up through radio frequency, infrared (heat), and right on through visible light to gamma rays. This massive release of broad-spectrum energy can cause large-scale disruption of radio propagation. lust as lightning striking an antenna will destroy a radio on its way to ground, the high currents generated in cables, overhead wires, antennas, and other conductors can destroy electrical equipment connected to them. This can cause loss of electrical power, telephone service, and other serious problems. But the EMP isn't through yet The large current flowing through all these conductors to ground generates a huge electromagnetic field, and that's the real problem for solidstate electronics, amateur radio included. When an electromagnetic field collapses, it will generate induced current in any conductor which happens to cut its lines of magnetic force. The magnitude...
Walker Scieniificns ELF-50 Field Monitor is a new. low cost monitor for measuring potentially hazardous tow level electromagnetic field radiation generated by power lines, TVs. VDTs, appl ances. and other equipment. It is a hand-held instrument thai measures the extra-low-frequency (ELF) etectro-magnetic field radiation generated from any AC 60 Hz device It 's easy to operate usl switch it on and pface it
Radio waves are electromagnetic waves similar in nature but much lower in frequency than light waves or heat waves. Such waves represent electric energy traveling through space. Radio waves travel in free space with the velocity of light and can be reflected and refracted much the same as light waves. Alternating current passing through a conductor creates an alternating electromagnetic field around that conductor. Energy is alternately stored in the field, and then returned to the conductor. As the frequency is raised, more and more of the energy does not return to the conductor, but instead is radiated off into space in the form of electromagnetic waves, called radio waves. Radiation from a wire, or wires, is materially increased whenever there is a sudden change in the electrical constants of the line. These sudden changes produce reflection, which places standing waves on the line.
Pair of D-shaped coils used in the older type. They have essentially no pick-up from a moderately uniform electromagnetic field and, when energized, they produce no such field in their vicinity. Accordingly, they may be used close to each other or to other circuit components.
The change in frequency of electromagnetic waves as a function of relative motion is now known as the Doppler shift. The phenomenon was first described by Johann Christian Doppler, a mathematics professor at the State Technical Academy in Prague, in 1842, in a paper delivered to the Royal Bohemian Society of Learning titled On the Colored Light of Double Stars and Some Other Heavenly Bodies (Magnin, 1986). Doppler shift varies directly with both the transmitted frequency and the relative velocity between the transmitter and receiver, and inversely with the speed of light. It is utilized in fields as diverse as aircraft radar (Shuch, 1987), spacecraft navigation, remote sensing, biomedical imaging, and of course satellite orbital analysis (Davidoff, 1978). To understand the Doppler shift for electromagnetic waves, imagine the headlight on the front of an approaching train, which is traveling at a substantial velocity let's say, mach 100,000, a tenth the speed of light. Now we know the...
The natural wavelength of a Hertz antenna depends primarily upon its length and secondarily upon such factors as may operate to change the distributed constants of the wire from those it Would have in space. The natural wavelength is approximately twice the length of the wire, as explained in Chapter Four. In practice the natural wavelength of the wire will be somewhat greater than twice the physical length, partly because electromagnetic waves do not travel quite as fast on wires'as they do in space, and partly because the antenna is in proximity to other objects, including the antenna poles, guy wires and insulators, all of which increase the distributed capacity and thereby increase the wavelength of the antenna. Because of the varying nature of these extraneous effects, the natural period of a given length of wire will differ with different surroundings. If the antenna is reasonably clear of other objects and is well off the ground, its natural wavelength will be between 2.07 and...
The wavelength in centimeters is obtained with sufficient accuracy by dividing 3 X 1010 by frequency. In most applications electromagnetic waves are characterized by their frequency, but in some problems the use of wavelength may be more convenient. It has been shown in the paragraph entitled Frequencies over 200 Mc, , above, for instance, how an unknown frequency over 200 Mc can be determined from the two frequencies of the heterodyne oscillator which produce successive beat notes. If all frequencies are converted into wavelength, the wavelength of the unknown is simply the difference between the two wavelengths which produced the successive beat notes. Example 160 and 200 Mc in the example above correspond to 187.5 and 150 cm. The difference of 37.5 cm corresponds to 800 Mc.
Propagation of Electromagnetic Waves. An a.c. current flowing through a wire produces a circularly disposed magnetic field about the wire in a plane perpendicular to the wire. The alternate collapse and reversal of the magnetic field due to the A.c. variation of current induces across the ends of the wire a voltage which is equal to the rate of change of the magnetic flux surrounding the wire and is in opposition to the applied voltage. The latter has, therefore, to overcome not only the resistance of the wire but also this induced component from the magnetic field and the voltage equation is represented by
In general, the radio receiver is a device designed to intercept the electromagnetic waves, which.are being transmitted by the sending station and convert them into audio frequency vibrations of such a character as will cause a response in the telephone receiver. This is accomplished in the following manner Figure 4 shows the layout of a simple receiving set, all of which, with the exception of the head telephones can be constructed by the beginner. A set of this description will afford excellent practice to one Just starting in to study wireless a3 it i3 suitable to receive code signals from nearby transmitters, A is the Antenna or Aerial, which is constructed of four lengths of No. 14 B. & S. gauge bare copper, each length approximately 35 ft. long and insulated from the spreaders at each end. For good reception the antenna should be from 40 to 50 ft. above the ground. The usual place for installation is on the roof of a house or suspended from the roof to a tree, making sure that...
Some have claimed that Doppler ascribed his principle of motion affecting perceived frequency only to sound waves, and then others extended it to electromagnetic waves. Not so. His 1842 work was titled Oaj the Coloured Light of the Double Stars and Certain Other Stars in the Heavens. He gave an oral presentation to the Royal Bohemian Society oi Sciences at the Patriotic Hall ol Carolinum on the same topic. He theorized that light from double stars (stars
The antenna or aerial consists of a network of wires suspended in the air and serves to catch or receive the electromagnetic waves from the atmosphere. In a transmitting station the aerial serves to radiate the waves out into space. For transmitting purposes it is desirable to have the antenna of special dimensions and design in
7900-Series drives are designed to operate in areas which have a large amount of electromagnetic interference. A line filter in the power supply removes severe line transients. Provision for electrically isolating the disc drive from the cabinet rack is incorporated in the chassis slides. This is accomplished without sacrificing grounding of all operator-accessible controls. The front-end frame assembly is grounded to the rack rather than to the main casting which is the disc system ground. Thus the disc system can be isolated for added protection from noise, such as that from static charges produced by walking on carpeted floors.
And panels are made of steel sheet because it offers easy fabrication, low tooling costs, and excellent shielding for electromagnetic interference (EMI). Fig. 6. EMI (electromagnetic interference) shielding detail. Fig. 6. EMI (electromagnetic interference) shielding detail.
Design of the control panel for electromagnetic compatibility was especially difficult since the control panel must contain any electromagnetic interference (EMI) generated in the high-performance logic system, and must protect the circuitry from electrostatic discharge (LSD). Mechanical and electrical design teams worked together to meet these stringent requirements. Interface circuits are filtered to remove normal-mode noise before cabling to the control panel. The filters also guard the internal circuits agains ESD-induced transients. The mechanical design minimizes the control panel's ESD entry points by using light pipes and a molded plastic enclosure. The inner surface of the enclosure is zinc-coated and electrically connected to the chassis to act as an EMI shield and a conductive path for ESD.
Figure 5a shows a piece of typical large-scale multi-board equipment, such as a microcomputer, in which plug in primed wiring boards are installed on a socketed motherboard. Usually, these PWBs will be mounted in a closed cabinet lor both ElectroMagnetic Interference (EMI) and aesthetic reasons. If we apply air broadside to the PWBs, only the first one in the lineup will benefit. Figure 5b
The metal backplate, in conjunction with the attached metal connectors and mating metal connectors on the cable, also provides a significant improvement in limiting EMI (electromagnetic interference) radiation. Since the cable can be disconnected at the backplate. the I O card is now-independent of the cable length and the system can be configured easily. The space chosen for the cards allows an increase in printed circuit board area from 174 square centimetres for the older 980xx series cards using two boards to 206 square centimetres for the new cards using a singleboard design (Fig, I). Electrical Architecture
To reduce electromagnetic radiation in the system environment, several techniques are used, Fig. 3. A line filter is used as well as two inner and two outer top and bottom covers. There are gaskets between plug-ins and mainframes, and beads between 14-module plug-ins. Also die castings are used for plug-in front panels.
An improved ac Power Switch by Raymond A Robertson A novel combination of solidstate switches and mechanical relays
Switching ac power on and off may seem simple we do it every time we turn on alight. But if you're concerned about electromagnetic interference or need a switch that'll operate a million times before it wears out, you have some problems. The article on page 34 describes a new ac power switch. Model 14570A, that's designed forten years of service switching power on and off under computer control in automatic systems, where interference can't be tolerated and 50,000 operations, the lifetime of a typical relay, may occur in six months.
Almost three-quarters of a century ago, Einstein explained how electrons are knocked out of solids by sufficiently short electromagnetic radiation. Yet until recently practical applications of this fundamental phenomenon have been limited almost entirely to radiation detectors, photomulti-pllers, and photovoltaic and photoconductive cells. That the escaping electrons contain Important information about the material from which they are ejected has been a recent discovery, dating back scarcely a decade. Einstein's theory of the photoelectric effect predicted that the ejected electron's energy should equal the energy of a quantum of the incoming electromagnetic radiation less the electron's binding energy. However, early measurements of the energies of escaping electrons were disappointing. There was little correlation between Einstein's simple relation and the energies observed. This lack of correlation wasn't too surprising, since electrons typically make numerous collisions with atoms...
This new lowcost radiant flux meter system gives direct radiometric measurements in the infrared visible and
Optical measurement is one of the oldest and most fundamental areas of science, yet it's still one of the least mature. Optical energy is generally considered to be the portion of the electromagnetic spectrum between microwave and x-ray frequencies.* Measurements in this region are a separate area of science because optical sources, detectors, and techniques differ markedly from those used in the microwave or x-ray regions of the spectrum. Within the optical region lie the visible wavelengths, those to which the human eye is sensitive. Fig. 1. Easy-to-use, low-cost HP 8330A 8334A Radiant Flux Meter System measures optical power in the ultraviolet, visible, and infrared regions of the electromagnetic spectrum. It reads directly in absolute radiometric units without spectral calibration curves. Maximum absolute uncertainty is less than 5 of full scale. Fig. 1. Easy-to-use, low-cost HP 8330A 8334A Radiant Flux Meter System measures optical power in the ultraviolet, visible, and infrared...
Much is being said in the technical press these days about fiberoptic communications. By now, it would seem, all electronics engineers are aware of the great advantages that optical fibers have over coaxial cable as a transmission medium, namely, a drastic reduction in weight and size for a given bandwidth, electrical isolation, immunity to electromagnetic interference, and a capability for secure transmission of information. So, in view of the explosive growth of communications beginning with essentially man-to-man messages and now encompassing transmission of complex information, computation, instrumentation, and control data the question arises why are fiber-optic links not in high-volume use The dielectric nature of the fiber contributes many advantages. An optical-fiber link maintains practically complete electrical isolation between transmitter and receiver, effectively eliminating ground loops. It is also immune to electromagnetic interference. Both of these properties are...
Electromagnetic interference (EMI) can cause errors of several dB, A spurious signal will add proportionately more power to the noise-source-off power measurement than Lo the noise-source-on measurement. This decreases the Y factor and thus increases the measured noise figure.
A special power transformer conforms to IEC and VDE (Verband Deutcher Electrotechniker) safety standards. The standard 5314A has exceptionally low electromagnetic emissions. Extensive environmental and life testing insure that this instrument will provide good measuring capability in a wide variety of applications.
THE MILLIMETER-WAVE PORTION of the electromagnetic spectrum lies between the microwave and far infrared regions. Generally, millimeter-wave frequencies are between 3Qand 300 GHz (wavelengths from 10 to 1 mm . The main applications for millimeter-wave systems are in communications, radar, and spectroscopic observation.
Once the basic architecture was chosen, work proceeded to design a tow-cost, low-power, electronic interface to the system. The combination of a custom CMOS (complementary metal-oxide-semiconductor) integrated circuit and miniature pulse transformers is the result. The electronic interface links each device to the next through a pair of wires using a floating, balanced, differential voltage mode of operation. This provides good noise immunity and reduces EMI (electromagnetic interference). Eliminating the need for a system ground avoids the problems often associated with ground loops and makes it easy for devices to float with respect to earth ground, a feature especially convenient for devices like voltmeters. The electronic design of the interface is discussed in the article on page 11. The design of the custom CMOS IC is described in the article on page 16,
This advance in SAW excitation initiated a new wave of interest in SAW devices to capitalize on their novel properties. Such devices are small because surface-wave velocities are typically 300U metres per second, five orders of magnitude slower than electromagnetic waves. The IDT is a planar structure that can be made with a single metallization step. Advances in microelectronic fabrication and photolithography brought about by the booming semiconductor industry were immediately applicable to the emerging SAW technology. The growing research led to new piezoelectric materials and material cuts optimized for particular requirements such as temperature stability nr large fractional bandwidth.
I have stated in this column many times that it is my belief that an amateur license is not a license to say anything you want, when you want, whether your language is welcome or not. Your license Is a permit granted to you by our government to communicate through the use of electromagnetic radiation on pre-determined spectrum in exact accordance with regulations as set forth by the governing body, i.e the FCC. If you are a jammer or thinking of becoming a jammer, then I suggest you weigh the potential consequences. By this action, the Commission has set a long needed precedent that can be used against you. They can take your license. They can take other punitive action. You might even wind up in prison, or at least have to pay a stiff fine along with court costs.
Time domain reflectometry (TDR) is a simple and accurate way to locate and analyze discontinuities in coaxial cables and microwave transmission systems.1 The time domain re-flectometer applies a fast voltage step to the cable or system under test some of this energy is reflected by discontinuities or changes in the characteristic impedance of the system then both incident and reflected waves are displayed on an oscilloscope. Because of the finite velocity of electromagnetic waves, discontinuities at different distances from the step generator appear as individual responses on the display, and their locations can be determined easily. The shape and magnitude of each reflection tell what kind of discontinuity is present resistive, inductive, or capacitive, series or shunt.
EARLY EVERY TEST SET includes a device to apply ac power to the unit under test. It may be a commercially available unit, but more commonly is specially built. It is normally a box containing a power supply, a relay, and a relay driver. Some of the fancier ones include inductors to enhance the life of the relay contacts and some sort of EMI electromagnetic interference) filtering. While these devices do the job, they generate EMI when turning on or off. Many are special, one-of-a-kind designs, and it is not only time-consuming to design and fabricate a rack-mounted box that has convenient input and output connections, but the finished product is sometimes less than ideal from the points of view of safety, reliability and electromagnetic compatibility.
Because electromagnetic energy, and the associated electrostatic energy, oscillates to and fro inside them in one mode or another, resonant cavities resemble wave guides. The mode of operation in a cavity is affected by the manner in which micro-wave energy is injected. A cavity will resonate to a large number of frequencies, each being associated with a particular mode or standing-wave pattern. The lowest mode (lowest frequency of operation) of a cavity resonator normally is the one used.
Manufacturers, vendors, and shippers of radio frequency devices thai emit electromagnetic energy capable of causing harmful interference to radio communications must meet the technical standards of FCC rules after October 1, 1970. The new order implements a 1968 law empowering the Con mission to make reasonable regulations governing the interference potential of certain devices. (Section 302, Devices Which Interfere with Radio Reception, was added to Une Communications Act on July 5, 1968, bv Public Law 90-379, 82 Stat. 290.)
The 5315A B is a moderately priced universal counter that accepts signals from dc to 100 MHz on both input channels. Its basic time interval resolution is 100 nanoseconds, but this may be improved on repetitive signals to less than a nanosecond through the use of averaging. The 5315A (Fig. 1) comes in a rugged plastic case that is suitable for bench use and can be equipped with an optional internal battery pack for portable and field applications. The 5315B is the same instrument housed in a standard HP metal package. The 5315B is useful for system applications or where superior EMI (electromagnetic interference) performance is required. Either instrument may be ordered with a temperature-compensated oscillator for applications where higher accuracy is necessary.
One only has to look at the communications industry to see what's happened. The crowded electromagnetic spectrum has been squeezed to make room for more and more channels. To guarantee that each transmitter remains within its allocated channel, its frequency must be controlled to within a few parts per million. Measuring frequency with this degree of accuracy requires an electronic counter. Or look at the vast network of telephone cable and equipment, over which millions of messages are transmitted daily. To keep it in working order, carrier frequencies must be measured and calibrated. Tone bursts must be counted. Millions of relays must be checked and timed. These are jobs for electronic counters.
In the past two years, ARRL's Educational Activities Department (EAD) has sponsored several technical workshops, beginning with an Introduction to Digital Signal Processing, which we have run four times. Additional workshops scheduled for 1994 are Electromagnetic Interference, which will be held September 30, in Boxboro, Massachusetts, in conjunction with the ARRL New England Division Convention, and Computer-Aided Design of HF Antennas, scheduled for October 21, in Concord, California, at the ARRL Pacific Division Convention (Pacificon). (Contact EAD at ARRL Headquarters for further information about these workshops.)
Why fool around with approximations and guesses You can know exactly whats happening on your coaxial cable
A step voltage applied to one end creates a power wave that reaches the load at some later time. Some of this power may return back to the sending end at a still later time. The two conductors (the center lead and the braid) are said to act as guide.s for this power wave,2 and that the electromagnetic energy is actually conveyed, in a mathematical sense, by the electric and magnetic fields that exist within the dielectric material. After the initial, or transient conditions, have all been resolved, this
In designing equipment to meet EMI standards, two basic types of EMI emissions are considered conducted and radiated. Conducted emissions consist of radio noise conducted through the ac power line. Radiated emissions consist of electromagnetic energy radiated from the equipment and connecting cables. When these tests indicated that an acceptable level of EMI performance had been achieved, quantitative measurements were made outdoors in an open field. A 52 x 60-metre elliptical area, oriented at right angles to nearby commercial radio transmitters, was cleared of all objects that could affect the electromagnetic fields. The equipment was placed at one focus of the ellipse and the measuring antenna was at the other. Tuned dipole antennas and tuned radio receivers of the VDE-recommended type were used to measure the electric field strength in the 30-to-1000-MHz range. The magnetic field strength was measured in the 10-kHz-to-30-MHz range using loop antennas and a tuned receiver. Analyses...
Electromagnetic pollution may be defined as the effects of electromagnetic interference (EMI) produced by man-made apparatus. The seriousness of this interference ranges from annoying interference that affects a radio or television channel to interference that causes failure of an important communication channel or a cardiac pacemaker. Electronic computers generate electromagnetic radiation that may range up to 1 GHz and beyond. This radiation is caused by alternating currents and voltages present in the computer hardware. The spectral content of these signals consists of both harmonic and broadband products.
Above the surface, the signal disappears or is greatly reduced. If one antenna is left below the surface, communication is possible with certain other types of antenna above the surface and at a distance- Communication can be achieved over a distance greater than that predicted by the normal electromagnetic radiation formula used to show the attenuation expected on an underwater path. From this, the proponents of tire Hydronics Theory deduce that there is a form of radiation from the transmitter somewhat different from electromagnetic radiation, possibly a form of energy heretofore not proven to exist, although hypothesized by some of the early experimenters in radio and electricity,
In preceding chapters, the component parts of transmitters have been presented in some detail. Here, the method of linking oscillators, amplifiers, modulators, antennas, and microphones into a single unit, called a transmitter, becomes the main problem together with observation of any new phenomena which result from the mutual influence of these parts upon each other. In a broad way, we realize that the transmitter must contain an oscillator in order to generate currents whose frequency is sufficiently elevated that appreciable electromagnetic radiation can take place from a suitably designed antenna, and that some means must be devised to add human intelligence to the emitted energy. Our transmitter (of the amplitude modulated type) must be so designed and adjusted that its frequency will remain constant also the carrier wave, when unmodulated, must not change in amplitude. In other words, we desire stable output. If we attempt to devise a single oscillator of...
The basic reason for this procedure in both carrier and radio systems is to make possible the transmission of a number of different signals over the same transmitting medium without mutual interference by placing each signal in a different portion of the frequency spectrum. In radio transmission, such a procedure is also necessitated by the fact that efficient electromagnetic radiation in space can only be attained at high frequencies. It should be noted, however, that the total width of the transmitted carrier frequency band cannot be less than the sum of the bandwidths of all the signals carried whether the signals are only a few cycles wide as in telegraph, or millions of cycles wide as in television.
The system should provide quick response to inquiries from its users. It should be possible for a salesperson to respond to a customer's inquiry and ascertain the scheduled shipment date of an order while the customer waits on the phone. High system performance and a powerful software architecture are required to support such transactions effectively while several other users are updating data bases, accessing files, writing reports, or developing programs at the same time. To be well-suited for the office environment, the system should consume minimal floor space and require no major changes to office facilities for installation. This means that no special temperature and humidity controls and no special power should be required. The system must be quiet, safe, and esthetically pleasing. There must be no radiated electromagnetic energy that would interfere with other equipment in the vicinity, and static discharges to the machine produced by walking on carpets during periods of low...
No photo of the trophy is available yet, because the original design work is still under way. It will have the general character and size of a conventional Oscar award, however, consisting of a male figurine about 15 inches in height. The figure will bear a lightning bolt representing electromagnetic radiation and will be supported on a small pedestai of marble encircled by a metal band for the inscriptions.
Electromagnetic fields are described in terms of volts or amps per meter, so the dimensions of the antenna determine the volts or amps that appear at its terminals. To confound the issue, the antenna s dimensions relative to a wavelength also determine the impedance of the source of voltage or current. The impedance of the anienna is resistive (resonant) only for particular lengths. The longer the antenna, the higher the maximum available power output, hut for some dimensions ir is very difficult to obtain the power that is available. For example, a full-wave dipole has a high impedance that is difficult to match. In short, bigger is
The major change on the new form is a certification to the effect that the applicant has *read and will comply with Section 97.13(c) of the Commission s Rules' regarding RF radiation safety and the amateur service section of OST OFT Bulletin No. 65. Evaluating Compliance with FCC-Specified Guidelines for Human Exposure to Radio Frequency Electromagnetic Fields. station could cause human exposure to RF electromagnetic field levels in excess of those allowed, you must perform an RF environmental evaluation if your transmitter PEP exceeds the following limits. SHF EHF (all bands) 250 W If the routine environmental evaluation indicates that ihe RF electromagnetic fields could exceed the maximum permissible exposure limits, you must take action to prevent human exposure.
(2) Pressing down a telegraph key causes a current to flow through the telegraph circuit. This current operates a sounding device at the receiving end. In radiotelegraphy pressing down the key also induces a current to flow through a sounding device in the receiver. In the telegraph circuit, the voltage is supplied by the battery, and the current is transmitted by means of wires. In the radio-telegraph circuit, the energy is supplied by a producer of radio waves, and the radio waves are transmitted through space by means of electromagnetic fields. (1) An alternating current flowing in a wire radiates energy into the space around it. This radiation is in the form of an electromagnetic field. If this wire forms the primary of a transformer, then the secondary of the transformer is cut by the magnetic lines of force which are part of the electromagnetic field. The magnetic lines of force expand and contract because of the alternating current in the primary. These magnetic lines, moving...
Electrical safety Harmful or lethal aspects of electricity safety procedures interlocks discharge ol power supplies disconnection of devices harmful or lethal aspects of RF and microwave energy (non-ionizing radiation) standards of exposure harmful or lethal aspects of antennas and erection controlled and uncontrolled environments hazards of portable and mobile operation. Interference with other devices ipacemakers) and other areas may be suggested.
Counters designed for detecting gamma radiation and fast neutrons need no window, because the glass envelope and the cathode are to a large degree transparent to these rays. Gamma rays, or photons, are flashes of electromagnetic energy which eject photo electrons from the surface of the countertube cathode in the same way that light causes the emission of electrons from a photo-sen
Already covered has been the propagation of electromagnetic energy, through both wires and space, as well as the ideas of voltage and current, resistance and reactance, and Ohm's Law for both ac and dc. We're now ready to attack such puzzlers as power, decibels, and harmonic frequencies.
Both Faraday and Maxwell studied and wrote, in quite a different style of course, about something they called displacement current , which left the conducting metal and jumped across the intervening space. This thing is of course electromagnetic energy and travels at the speed of light. I expect it would, being emitted in quantum style and thus made up of photons
Moreno1 defines transmission lines as a system of material boundaries forming a continuous path from one place to another and capable of directing the transmission of electromagnetic energy along this path. In wideband practice at higher frequencies, where the principle mode (TEM) of transmission is used, coaxial structure is the type most commonly used. For quite some time standards have been established in coax. Connectors have been correspondingly standardized. Attenuators, as one of the basic building blocks of measurement systems, are developed to fit these standard transmission lines. With the advent of thin film technology, new types of attenuator realizations have come about, transforming the coaxial transmission line into a plane, allowing the use of precision thin film techniques.2
ELF Electromagnetic Field Radiation Measurement ELF-50C3 Measure potentially hazardous ELF Electromagnetic Field Radiation generated by Video Display Terminals (VDT's), TV sets, home appliances, industrial machinery and other similar devices, calibration traceable to nist
Various organizations and countries have recommendations and laws establishing limits on the levels at which computers may radiate. MIL-STD-4611 is a military document of the United States Government that is used as a control standard, primarily for procurement of military equipment. The Federal Communications Commission of the United States currently has a proposal specifying that the electromagnetic field at a distance of k 2ir shall not exceed 15 V m, where A is the wavelength of the signal. At present, the FCC regulation regarding computers is not very specific, merely prohibiting harmful interference. Comit International Sp cial des Perturbation Radio lectriques (CISPR), which operates under the auspices of the International Electrotechnical Commission (IEC), is an international organization that seeks to establish international agreement on EMI limits. CISPR publication 112 has limits on industrial equipment covering frequencies between 0.15 MHz and 18 GHz. The limits are...
ELECTROMAGNETIC FIELD METER flsduce exposure to potentially harmful electromagnetic fields, AlphaLab's handheld TrlField Meter measures AC eleeiric fields, AC magnetic fields and radio mtcrowave power density. Find ground faults, AC current wires or measure hlgMietd generators with the Magnetic setting (.2 - 100 milligauss, 60 Hi) identify poorly grounded or shielded equipment, high VDT or fluorescent light fields, distinguish hot vs. ground wires with Electric setting (.5 - 100 kWmf 60 Hi) measure antenna radiation patterns, leaky microwave ovens, eic, on BF microwave setting (50 MHz to 3 GHz, .01 to 1 mW cm2 + AlphaLab, 1272 Alameda Ave. Salt Lake City, UT 64102 CalJ (801) 532-6604 for speedier service or free literature on electromagnetic radiation health risks.
Electromagnetic field, (3) ample output for use as a source for high frequency measurements, and (4) a convenient physical size. A good compromise between these conflicting requirements has been achieved in a new oscillator utilizing a vacuum tube1 especially designed for the ultra-high frequencies coupled to a lumped concentric-element tank circuit.
An electric field E accompanies a moving magnetic field, just as a magnetic field H accompanies a moving electric field. The fields, if in motion, are always associated together. It can be shown that they are at right angles to each other, that both are at right angles to their motion, and that they contain equal amounts of energy. They are spoken of jointly as an electromagnetic field. In 1864, Clerk Maxwell said that light, passing from a source to an observer, consisted of electric and magnetic fields in motion. He predicted that there should be other electromagnetic waves of comparatively low frequency. These were found in the laboratory work of Heinrich Hertz in 1887, and are now called radio waves. 8.2 Radiation. When an alternating current starts to flow through a conductor, its electromagnetic field builds up, with the lines of force in a certain direction, until the current has reached its maximum. Then, as the current decreases, the field continues to collapse back into the...
With a high standing wave ratio* What is needed then is a method of remotely tuning the antenna to keep it matched, or nearly so, to the transmission line, Many schemes have been tried with varying degrees of success and currently the most popular centers around either a tapped or continuously variable rotary inductor, iliis article offers a different solution to this problem in the form of a remote tuning unit that uses a variable capacitor for the tuning element. This technique, in general, is more economical in that the rotary variable inductors are expensive whereas a variable capacitor can usually be salvaged from the junk box, If the power is low, that is, less than about 15 watts, a receiving type capacitor can be used* It also appears that there is less contact loss in. the capacitor than in the inductor. For what it is worth, it is also noted that the electrostatic field of the capacitor is much easier to shield than the electromagnetic field of the inductor* Also a more...
Experiments conducted in 1888 by a young German scientist, Heinrich Rudolf Hertz , showed that by connecting the terminal of a spark coil to two brass balls separated by a small gap, Fig. 1, that the spark caused a disturbance which produced electromagnetic waves. This apparatus is known as the Hertz Radiator or Oscillator, and these waves have since been called Hertzian waves.
Triacs are capable of generating a considerable amount of electromagnetic interference. This interference is proportional to the turn-on dv dt so it can be minimized by firing a triac only when the voltage is low. The current through a triac, on the other hand, must be greater than a certain minimum, known as the latching current, if conduction is to be sustained. There thus exists an optimum time for firing a triac late enough in the ac cycle for the current to be above the latching level but not so late that the dv dt would
All of the EMI objectives set for the 9835A B Desktop Computer have been met. The product has passed the legal requirements of VDE for both conducted and radiated electromagnetic interference. VDE tested the 9835A both separately and as a system. The system consisted of a 9835A, a 9885M Flexible Disk Drive, a 9866B Thermal Printer, and a 9872A Plotter. The 9835A B has passed other internal specifications such as static discharge to 15 kV, line transient tests, and susceptibility to EMI fields.
Another aspect of the machine is the electrical interconnection system, which includes the power cord, I O cables, printed circuit boards, and the wire bonds to the integrated circuits. Cost, safety from shock hazard, international safety standards, durability, and immunity from electromagnetic interference (EMI) and electrostatic discharge (ESD) are important concerns. The printed circuit boards are also a level of packaging, with parameters of size governed by interconnect cost, packaging density, system partitioning,
Meeting the required electromagnetic interference ffiMl) and susceptibility goals was a bit more challenging than initially expected. Large-amplitude RF fields tend to generate voltages on exposed cabling and circuits. These voltages overdrive many of the active circuits, causing nonlinear operation and distortion. To avoid direct exposure to these fields, the analog circuits are housed in an internal HM1-tight box. The box has an aluminum frame around the sides. The bottom cover is the ground plane of a printed circuit board and the top cover is a removable EMI-tight lid. Removal of the lid. which is held in place by only two screws, makes all the circuits available for service. The microprocessor boards are sufficiently shielded by the instrument cabinet and do not require the extra shielding To keep the RF fields from developing voltages on the cabling feeding the circuits, special precautions were taken. First, from the inner box to the front panel, shielded cable is used. Second....
Heart pacemaker wearers Numerous letters to the- r rn journals indicate a growing need for information about EMI Electromagnetic interference , especially as it 'elates to ham oper aiingl Pacemaker wearers generally do not have access to reports of EM susceptibility tests made by military and or f e d e r a 11 y sponsored FDA BRH testing programs. As a result, the lack of relevant in form a Tion leads to confusing and often erroneous, ' advice from well-meaning buT ill-advised individuals
Computers and their peripheral devices, like many common household appliances, emit electromagnetic Interference (EMU Ordinarily these emissions pass around us, unnoticed until the television or radio show we are listening to is interrupted by noisy reception. Current government standards aimed at limiting EMI, as well as a desire to reduce unwanted Interactions between computers, have prompted the following design goal tor the HP 2700 EMI suppression commensurate with the many requirements of a powerful desktop peripheral.
Sounds audible to the best human ears lie in a frequency range of about 20 Hz to 20 kHz. But acoustical energy is by no means limited to this range. Just as the human eye responds to only a small portion of the electromagnetic spectrum, the human ear provides man with only a part of the information that could be extracted from sonic energy.
Our cover subjects this month can barely be seen in the cover photograph. They're the two tiny specks in the middle of the flat plate In the foreground. They are spheres of barium ferrite that serve as the frequency-sensitive elements of magnetically tunable bandpass filters for the millimeter-wave frequency range. (The millimeter-wave range is the region of the electromagnetic spectrum from about 30 to about 300 gigahertz. It's becoming more important as radar, communications, and other systems move to higher I freauencies seekina hioher Derformance or less crowdinn.l These filters are
One of these jumps is termed the Lyman Series. Only about one atom in a million in the soiar atmosphere is excited to this state. However, this is enough to emit energy in the ultraviolet portion of the electromagnetic spectrum. Radio waves make up a small part of the electromagnetic spectrum. The spectrum consits of radio waves, infrared, visibile light, ultraviolet, X-rays, and gamma rays. The sun radiates all forms of energy along the electromagnetic spectrum. However. the sun itself along with the earth's atmosphere and ionosphere - filter out
The great Maxwell said that there was a medium for electromagnetic waves. He confidently assumed other physicists ( Natural Philosophers ) would discover this. But, as you know, they did not do so, and, one hundred years being quite a time to wait, it became unfashionable to talk about this aether. After all, if you were unable to find it, even though you know a wave has to have a medium, and being a professor you had to teach something, the only thing you could do was to make it an out thing and stop talking about it. Maybe then people would stop trying to make you admit you didn't know. You can also fall back on the
The principle of operation involves immersion of the transistor radio in two electromagnetic fields. Both of these fields are at frequencies within the passband of the i-f amplifier of the radio. (Because of the proximity of the oscillators which generate these fields, we have considerable latitude with respect to where these frequencies enter the response curve of the i-f amplifier.)
The history of cesium beam clock development has its roots in the discovery of quantum mechanics although exploitation on a large scale dates back only about two decades. The knowledge upon which cesium beam clocks are based developed from the study of the absorption and emission of electromagnetic radiation by matter. The concepts of the electron and the nucleus of the atom, the quantization of the energy of atoms, and the quantization of the electromagnetic field, discovered by Thompson, Rutherford, Planck, Einstein and Bohr, combined with the theories of Schroedinger and Heisenberg in 1926, led
A circuit is called an antenna when ir radiates (transmits) into the atmosphere radio frequency (RF) energy that passes through it and or to intercepts (receives) electromagnetic waves. HF High Frequency. A section of the electromagnetic spectrum from 3-30 Megahertz (MHz). The 80-10 meter amateur bands are HF bands. Worldwide amateur communications occur most often on these bands. Polarization The orientation of the electromagnetic field of the antenna in relation to the earth. The electrical field of a wave is generally parallel with the active elements) of the antenna. RF Abbreviation for radio frequency energy. The RF portion of the electromagnetic spectrum ranges from about 20 kHz to 30 GHz, which is divided into eight frequency ba nds, from VLF (very low frequency) to EHF (extremely high frequency).
The HP-IL is a two-wire balanced differential interface with both transmitter and receiver electrically isolated from the interface cable. The isolated operation (there is no ground on the wires) eliminates many system noise problems such as electromagnetic interference (EMI) susceptibility and radiation. This is especially important because
8EHIMD THE DIAL -Tr-5 book exptians. in j.tall A aT s going on on v t e Irequefictos from r*noriwave up to microwave n gives the reader a good itiea o what he can find and where to find It, including sorr of the secret stations such as the C.I.A and the F.B.I, Everything is covered short of microwave monitoring. Anyone interested m purchasing a snorts avr receiver should have a copy of this book surveillance, station layout consideration, antenna systems, interface, and rhe electromagnetic spectrum, are Included SK73Q7 S4 95
The 9835A B is similar in hardware design to Model 9825A.1 In language and performance, however, it resembles System 45 (Model 9845A).2 It provides most of the high-level capability of System 45 and adds significant new capabilities. It extends and allows for further extension of memory, it provides a low-level language with a refreshing ease of use, and it meets new standards for electromagnetic interference.