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Want to get more out of the basic search box? Read about Search Operators for some powerful new tools. You will be surprised at how many times the connector is installed, only to find that one of these components is still sitting on the workbench The second step is to prepare the coaxial cable.

Using a small pointed tool, carefully unbraid the shield. Be sure to separate the strands making up the shield. Lay the unbraided outer conductor over the adapter Figure Make sure that the shield strands are neatly arranged, and then—using side cutters— neatly trimmed to avoid interfering with the threads. Once the shield is laid onto the adapter, slip the connector over the adapter and tighten the threads Figure Some of the threads should be visible in the solder holes that are found in the groove ahead of the threads.

Soldering involves using a hot soldering iron. The connector ivill become dangerously hot to the touch. Handle the connector with a tool or cloth covering. After you make a final test to make sure there is no short circuit, the connector is ready for use. Some general rules or guidelines are: 1. For all types of transmission line, you want to avoid extremely sharp bends and kinks.

Getting the transmission line inside the house is a bit of a trick. If you have brick or masonry walls, then a hole can be drilled in the wall at an appropriate place. A hammer and star bit can be used for those who like hard manual labor. Most people would prefer to use a tungsten carbide masonry bit on a slow-speed electric drill to make the hole. Be sure to wear goggles when doing this job, for dust and chips fly about and are danger- antenna. If it is necessary to route transmission line around a corner, then make the turn over a gentle arc with about one foot radius or more.

Avoid, wherever possible, running transmission lines close to metallic objects such as gutter downspouts. Run the transmission line along a wall, floor, or roof using stand-off insulators Figure There are several types, all originally made for the TV antenna and cable TV industries, and they differ in the manner of fastening: machine screw, wood screw, and case hardened masonry' nail types are all readily available.

Care should be taken on roof installations to not penetrate inside the roof; otherwise, a water wicking situation will exist and it could rot ous to your eyes. Cinder block walls are used on a lot of houses, and even brick houses frequently have cinder blocks in the basement and for a few feet above the surface. Cinder block is usually built with two hollow chambers see Figure , one on either side of the center line. The best place to drill the hole is in these chambers.

To find an appropriate spot, first find the center line of the block. Once the center line is marked, split the distance to either edge and drill at that point it should be right in the center of the block, if the block was built normally. Keep in mind that an extra long bit is needed for drilling through most cinder blocks eight to 14 inches thick, depending on the block. There is a right way and a wrong way to install cable at the wall entrance site.

Figure 5 shows both ways. The wrong way is to bring the cable in from above, and then pass it through the wall. The problem is that water runs down the cable and into the hole. There are two steps to avoiding water Side View damage.

Small Antenna Handbook

Inspect the seal every so often six to 12 months to guard against deterioration or trauma damage. Figure 4 15 Transmission Lines t 49 Wood frame and siding houses like mine are even easier to install a transmission line in. Figure shows a method that I used on several occasions. You above grade. The inside of the frame is covered with dry wall, while the outside is covered with plywood sheathing and aluminum siding some houses use vinyl siding.

This method ol construction is shown in cross section in Figure In some houses, like mine, there is a ten inch space between the top of the cinder block, which is two feet above grade, and the heel plate, and this space is occupied by the floor joists for the first floor above the basement. I am able to drill holes in this space to the outside, and that is where my antenna transmission lines pass into the house. Alternatively, as shown in Figure , a fist sized or smaller square hole can be cut in the dry wall in an unobtrusive spot to accommodate locating the cable.

In either case, you can either pass the cable can fashion a flat piece of wood planking 1x6 works nicely, as do narrower widths to fit under the moving part of the window. At least one friend of mine used a 4-inch high metal panel intended for a rack mount for this purpose. Coaxial barrel connectors, stand-off feedthrough insulators and other connectors can be mounted on the wood panel to pass antenna wires into the house. The connectors and the top, bottom and side edges of the panel should be caulked against the weather. A little glass putty, and the panel is secured in place.

They will shake their heads in pity, amazement, and despair at your embarrassed expense.. They are not necessarily optimum from a technical point of view; indeed; they are probably NOT optimum, but are often the best choice for nontechnical SWLs because of practical considerations. Random Length Antenna Perhaps the most common shortwave antenna in the entire world is the random length wire antenna shown in Figure The random length antenna is untuned, and consists of a healthy length of wire strung up between two supports.

The antenna wire should be 14 hard drawn stranded copper wire, or preferably 14 stranded steel wire that is copperclad to lower the resistance to radio frequency signals. The ends of the wire are supported by end insulators El in Figure and a rope to the support structure. The supports for the random length antenna can be the house, a nearby tree, or a wooden or metal mast erected especially for the purpose.

It might be convenient, but it could also be dangerous.. The antenna wire should be well clear of the support structure, so use at least five feet of rope and more if needed. For well filled- out trees, the antenna wire should be entirely clear of the leafy crown of che tree so that no physical interference and therefore potential damage or signal loss occurs. The signal is carried to the radio receiver by a downlead. The downlead consists of a length of insulated wire of 14 to 22 size. It must be insulated, even though the antenna wire need not be insulated, for both safety reasons and to prevent signal loss by accidental grounding.

The random length antenna can be erected at almost any angle, from sloping downward to straight up in the air in which case it is a vertical. The best performance will be seen if the antenna wire is horizontal to the ground and is as high as practical. After all, if you can afford a foot tower, you can afford a better antenna! The random length antenna works best if the wire is run in a single direction so there are no bends in the wire as it runs from one support to another. If you must bend the wire, however, this can be done with minimum violence to its performance.

Many people simply run the downlead into the house, directly to the radio receiver, without going through a lightning arrestor. Lightning strikes are not very likely, but if they come the arrestor will divert a large portion of it to ground. The lightning arrestor may save the receiver no guarantees, however , and is likely to prevent the house from catching fire again. Nature does what it must so no guarantees. Even if the house does catch fire, your insurance is more likely to pay off if an approved lightning arrestor is used in the circuit.

The ground connection is necessary for the antenna to reach its best performance. Some shortwave receiver manuals recommend a cold water pipe as the ground. Even if you have metal pipes, it is usually preferable to use an eight-foot copperclad steel ground rod driven into the Earth so that only a few inches show. The ground wire from the receiver and the lightning arrestor should be as heavy as possible bur for different reasons. Use it if you please, but realize that other alternatives exist.

The "Tee" or "Top Hat" Antenna The dee antenna shown in Figure is a reasonably popular version that is related to the random length antenna of Figure It differs from the random length antenna in that a portion of the downlead is used as a vertical antenna section. The vertical section should be ten to 30 feet long, and runs at a right angle down from the antenna wire.

One popular way to make a Tee antenna is to place the downlead connection directly over the point on the house where the receiver is located or where the wire goes into the house. It will make a convenient antenna for those readers who have supports like trees that would take the antenna wire directly over the building. As in the case of the random length antenna, use a lightning arrestor and ground connection with the Tee antenna. That means that the impedance ol the antenna varies with frequency and can show wide excursions Antenna Wire 30 to feet Downlead EI R Vertical Section Lightning Arrestor Receiver o Figure over a large range of possible values.

There are actually three cases in which 54 a Receiving Antenna Handbook this tuned random length antenna might be used. If the antenna wire is less than a quarter- wavelength long at the operating frequency, then the inductor is inserted into the line with the antenna wire.

For use with the L-section coupler shown in the inset, the antenna element needs to be greater dtan a quarter-wavelength. There are several antenna tuning units which are commercially available and suitable lor tuning random wire or dee antennas. Any wire antenna is enhanced by using a series of quarter-wavelength radials connected to the ground point.

The ground rod is also used for lightning protection , but the radials improve the performance on the bands for which the radials are cut. For the sake of pedestrian safety in your yard, bury the radials a few inches underground. The Window-Coupled Random Length or Longwire Marconi Antenna Random length and longwire antennas the two are sometimes confused with each other are easily built Marconi-style antennas.

They consist of a radiator element consisting of a length of wire Figure , supported by end insulators El and ropes R. An insulated wire downlead is routed through a window or wall to the receiver. The long wire has a length that is at least two wavelengths long 2A. There is a solution: use a ivmdoiv capacitor.

Cement copper foil on both sides of the window pane Figure , so that the two pieces register with each other without overlap. Solder the downlead to the outside piece of copper, and the lead to the receiver to the inside piece of copper. The solution to this problem is to place a resistor R1 in Figure between the ground and the downlead. Use a value of resistance between kilohms and 2 megohms. However, in constructing the resistor use at least ten 2-watt resistors in series; i. It will mold into the channel that receives the moving part. The window is then dropped down onto the flat strap.

If you live in a cold region of the country, then you might want to eidier use a different approach or be sure to seal the window. One type is round, and will mold directly to the window sill and sash see inset in Figure The Dipole and Its Relatives Chapter 6 J D ipoles have long been favorite antennas with receiver owners, and there are several reasons for this popularity. One of them is that the dipole has a bit less than 2 dB gain over an isotropic radiator because it is bidirectional instead of omnidirectional Figure For a transmitter, antenna gain provides increased effective radiated power in the transmission direction.

There is no real increase in actual power, but because the total power is directed into limited directivity it acts as if there were more power being generated.

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Regular Dipole Figure shows the simple dipole. Use 12 or 14 wire size; smaller sizes tend to break too easily. Because the dipole usually must work over a wide range, it is normally cut for a frequency close to the center of the desired band of operation. Suppose we want a dipole cut to a frequency of kHz with an overall length of L and the length of each element A.

Thus, the antenna is made of two wire elements, each being 19 feet and 11 inches long. The radiator element is broken into two portions, each of which are half the length found by the equation above, or a quarter-wavelength long. The ends of the wires are tied off to a rope mechanical support via ceramic, glass, or plastic end insulators El in Figure The feedpoint, where the line to the receiver is connected, is the center of the antenna where the two quarter- wavelengdi radiator elements are supported by a center insulator or balun transformer.

This pattern is azimuthal—that is, as viewed from above. It consists of two main lobes along the same maxima axis, with low-reception nulls along an axis at right angles to the main lobes. The pattern of Figure is actually only a partial view. It represents only the horizontal cut. The horizontal figure-8 pattern is the pattern from the ideal of Figure C is due to reflections from the Earth's surface immediately below the antenna combining with the radiated signal.


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  6. Azimuthal Pattern seen from above shown at Figure B, while the vertical extent for a perfect dipole in free space is shown in Figure C. The version shown in Figure C is for a perfect, free space dipole. Figure A shows the approximate pattern Irom a dipole located a quarter- wavelength above the Earths surface, while Figure B shows the pattern existing when the dipole is a half-wavelength above ground. The angle d in Figure B is the radiation angle. This angle is critical when determining where signals will be received from at any given time and frequency.

    Dipole Feedpoint Impedance When a dipole is electrically excited, either by a transmitter at the feedpoint or by an intercepted radio wave, an electrical current flows in the radiator. This current oscillates back and forth at the transmitted frequency. Unfortunately, the situation is not so simple in real life. The coaxial cable makes a good impedance match for most practical dipoles. You need to identify or build two support points: a roof peak, wall, tree, mast, and so forth.

    The path between the two support points is ideally oriented in the direction to be rejected—at right angles to the direction of desired signals. The actual length will probably be slightly shorter, although there is a small possibility of it being a bit longer. Also, when twin-lead is used, the velocity factor of the specific brand that you buy may affect length. The actual length is found by trimming or lengthening the antenna from the formula length, until minimum VSWR is reached on the frequency of operation that you desire.

    The twin-lead is stripped at the ends, the exposed wires are twisted together, and then soldered see Inset A of Figure Similarly, one ol the wires in the twin-lead is snipped at the center and about one-half inch stripped back in either direction. Figure The Dipole and Its Relatives t 63 The Q feedline to the receiver is not a good match to the 50 12 output impedance used by most equipment sold today.

    In addition, this transmission line is balanced, while the standard receiver antenna input is unbalanced designed for coaxial cable. Many experienced people prefer this method to the twin-lead method. The best insulators are the ceramic types that arc made for the purpose, but these are hard to come by these days except at hamfests. Each insulator is secured in place by a tie wire made of the same wire stock as the antenna radiator Inset A in Figure The tie wires are twisted and then soldered.

    The feedline is Q, parallel transmission line, and it is connected to the radiator between the center insulator and the strain relief winding. Both the electrical connection from the transmission line and strain relief wrapping are soldered. The end insulator is similarly handled Inset C in Figure A spreader insulator at each end is wired in the normal way Figure , Inset A , but the ends of the radiator are twisted together in a normal insulator for support by a rope.

    If you use regular parallel wire antenna insulators, then it is possible to buy a type with a hole in the center. As with all antenna connections, the end connections and tie wires should be twisted tightly together and then soldered. When the antenna radiator elements are identical sizes, and the spacing is lour to six inches, then the impedance transformation is , as for antenna folded dipole. Other values from 0. If you use the 1 5th edition, look on page As a result of transforming the feedpoint impedance, this antenna can be fed from 75 12 coaxial cable. Using a balun transformer at the feedpoint also helps the antenna pattern by balancing the currents in the two halves of the radiator.

    In practical antennas, it can get quite ragged, but with a balun at the feedpoint it comes much closer to the ideal. Because twin-lead uses 16 or 18 wire, and it is typically soft-drawn copper rather than copper clad steel, these antennas break a lot. A little wind, or a bit of ice, and plooop! Regardless of the mechanism, however, the result is the same: you re out of business until repairs are made. He chuckled, and then drew out a little drawing A series of five screw holes are made at the points indicated. The twin-lead is prepared by using a drill, leather punch, or ordinary paper hole punch to cut holes into the twin-lead.

    The twin-lead is fastened to the insulator block using nylon NOT metal machine screws and hex nuts. Fortunately, there are some things that can be done for the situation. This antenna is called the inductively loaded shortened dipole. The inductor should be designed to have an inductance of Q at 7. You can do this by adjusting either the inductance or the overall length of the antenna. Use a noise bridge, impedance bridge, or some other means for finding the resonant point. In each case, the coil is supported by an insulator ol the sort used for the end and center insulators.

    Usually, the shorter versions of the Figure Figure insulators work best. The coil is sometimes connected exactly as shown, while in other cases where the coil is larger diameter the insulator passes coaxially through the center of the coil. Figure B shows the same type of mounting for a coil wound on a toroidal core; Figure C is similar but uses a larger size toroid that can be slipped over the insulator. A pair of commercial dipole loading coils are shown in Figure The coil is made from insulated wire wound in the space between the end caps.

    These are available from a variety of ham radio and electronics parts sources. Countryman W3HH , once called it a "squashed rhombic" antenna. The antenna is a widely spread folded dipole, and is shorter than a conventional folded dipole. We need to calculate the lengths from the feedpoint to the middle of the spreaders , which is also the length from the middle of the spreaders and the terminating resistor. For example, at 7 MHz the lengths are Thus, the overall physical length, counting the two element lengths and half of both spreader lengths, is [2 x The termination resistor can be mounted on a small piece of plastic, or alternatively as shown in Figure , it can be stretched across the end insulator in the manner of the inductors in the previous section.

    Use a Q, 2-watt resistor for this application. Resistor antenna. First, the method of Figure is basically two dipoles connected to the same feedline, but tuned to slightly different frequencies. Thus, an antenna cut for a half-wavelength on kHz, is also a 3 A-wavc- length resonant antenna for 3 x kHz, or kHz. The simplest, most straightforward method of multibanding a dipole is to connect several dipoles to the same feedline, as shown in Figure The antennas can be harmonically related to each other only if the even harmonics are used third harmonics are already resonant—see above. Use the usual formula for a standard dipole to determine the physical length of each antenna.

    Some people use a single multiconductor cable to form the dipole sections. For example, electric cord two conductors , antenna rotor wire four or five conductors , and computer flat cable up to conductors! These wires are, however, weaker than regular antenna wire and antennas built with them will most likely have a greater failure rate than regular antennas.

    Carolina Windom Compared with Dipole - 20m: 4NEC2 using a .EZ file from ARRL 22nd Ed. Handbook

    Each trap is a parallel resonant inductor L -capacitor C tuned circuit. One of the properties of the parallel LC tuned circuit is that it offers a high impedance at its resonant frequency but a very low impedance to all other frequencies. The resonant frequency is also affected by the inductor of the trap, and follows rules approximating those of the loaded trap dipole in the previous section.

    Figure shows a commercially available trap for shortwave antennas. Figure shows a long multiband trap antenna that is usable for a large number of bands. Each trap Tl, T2, T3 is resonant on successively lower frequencies. Otherwise, the antenna is very similar to the trap dipole of Figure Two common impedance ratios are and For receiving antennas, the FT and FT sizes are adequate.

    Typically, for the 3 to 30 MHz high frequency a. Each transformer is either bifilar or trifilar wound. That is, each turn consists of two or three wires wound close together, depending on the design. Note that it uses three windings, trifilar wound, on a single core. The reason is simple, especially when one looks at the antenna patterns produced by conventional dipoles with and without a balun transformer at the feedpoint. The idealized figure-8 pattern that is normal for a dipole is distorted by radiation caused by currents flowing on the outside conductor of the coaxial cable.

    Ideally, this current is geometrically balanced by currents flowing in the opposite direction in the inner conductor, but that ideal is rarely achieved. The problem is alleviated by the balun transformer, and the pattern restored to very near the ideal. This transformer uses two bifilar wound windings ever a single core.

    Both of the balun transformers shown in Figure A and Figure B are broadband RF transformers, and will cover a wide range of impedances.

    Practical Antenna Handbook 5/e

    The balun transformer of Figure C is a little different. It uses two silvered mica capacitors for frequency compensation. This winding protocol differs from the other baluns where all windings have the same number of turns. Chapter 7 J Lon gw! These antennas become more manageable at higher shortwave frequencies, such as the 19, 13, and 10 meter bands, where one wavelength is relatively short physically. He at First thought it was an old-fashioned telegraph line, bur later found out that it was a low VLF band Vee-beam longwire antenna that was 24 miles long per leg!

    Vic officially visited that radio station later during the same trip in his capacity as the director of a U. Coast Guard engineering laboratory. My First experience with longwires was a little unusual, especially since it occurred in the two-meter amateur radio band to MHz where longwire antennas are not exactly common. A ham radio club station was located in a local Red Cross chapter house. Our first contact was a chap we had worked many times before; he was located about 90 miles to the cast. That evening, he was louder than normal good conditions?

    At first, we thought he had installed either a new antenna or a power amplifier, and made some comment to that effect. Its foot length was more than 12 wavelengths long at MHz— far more than the minimum requirement for a longwire antenna. Furthermore, the main lobes of such a long longwire antenna would be off the ends of the antenna and was thus pointed at the other station. Of course, the frequency selective traps were ineffective at two-meter band frequencies.

    When I used it in July , it performed a whole lot better than I anticipated. Another receiver advantage is that its very long length provides a very large aperture, so the amount of signal energy captured is also large. DX antennas need low, horizon-kissing angles. Finally, there is a diversity effect sometimes seen on longwires. In addition, there is a related class of antennas called Beverage or wave antennas.

    We will discuss all of these antennas in this chapter. A fundamental form of longwire antenna is shown in Figure It is the interaction of the waves on the various sections that forms the pattern for reception. Because the lowest frequency in the band is 4. This is contrary to the practice on other forms of antenna where a frequency in the middle of the band is selected e. The interference between the forward and reflected waves sets up stationary standing waves of current and voltage along the wire.

    A nonresonant longiuire is terminated at the far end in a resistance equal to its characteristic impedance. When the wire is 20 to 30 feet above the ground, Z Q is about to Q. The angles of the lobes vary with frequency, even though the pattern remains unidirectional.

    Practical Antenna Handbook

    The directivity of the antenna is partially specified by the angles of the main lobes. Figure A shows how angles of the main lobes change with respect to antenna length in wavelengths. For the sake of comparison, the gain over a dipole is shown in Figure B. Thus, when an antenna is cut for a certain low frequency, it will work at higher frequencies, but the directivity characteristic will be somewhat different at each end of the spectrum of interest.

    Figure Directivity AngleCX. This complexity is due in part to the fact that the hall-wavelength segments radiate or receive out of phase with each other.

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    If all segments were in-phase, then the patterns would be somewhat simpler. Between all ol the lobes are sharp nulls in which little reception is possible. As the lobes pull in closer to the wire, the number of minor lobes increases. At 5A. Also, the number of minor lobes increases to sixteen. The minor lobes tend to be -5 to dB below the major lobes. When the longwire gets very much longer than 5A. The current loops occur in the middle of half-wavelength segments. For multi-frequency operation the best solution is to end-feed die antenna.

    It uses an antenna tuning unit right at the antenna feedpoint. The impedance to be matched is typically Li. An argument for this system is that any practical untuned parallel transmission line will re-radiate some signal, contributing an unwanted vertically polarized element to the antenna pattern. By placing the ATU at the feedpoint, the problem is greatly reduced—coax, properly terminated, is less likely to re-radiate titan open feeders.

    It is quite suitable for nearly all SWL applications and is less of a hassle than open line. A disadvantage of the simple Zepp feed method is that the integrity of the antenna pattern depends on currents in both parallel conductors being equal. At other frequencies, the currents are unequal and that increases the pattern distortion. You can either purchase such line ready-made or make it yourself.

    This matching system only works on a single band. The radial is a wire that is cut to a quarter-wavelength in the center of the band of interest. A method for using coaxial cable transmission line is shown in Figure In this version, a balun transformer Tl is inserted at the feed- point.


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    8. Radials are a key component to resonant longwires—indeed, for nonresonant longwires too. Unfortunately, the radial is also relatively long and may consume a bit of valuable lawn space needed for the longwire. It is possible to shorten the radial length by inserting an inductor in series with the radial Figure For example, in the to kHz international shortwave broadcast band, the center frequency is kHz.

      The coil makes the antenna tuning a little sharper, but this is a reasonable trade-off for most users lacking proper Figure space. The resistor should be either a carbon composition or metal fdm type because those are noninductive. However, there are two easily implemented solutions to the problem. If possible, the resistor should be shrouded inside of a waterproof plastic box. This method places the resistor at the top of a six to eight foot copperclad steel ground rod driven into the ground so that only a few inches show.

      There should be at least four radials per band, although one or two are better than none. As always, the radials should be buried for safety reasons— pedestrians can trip over radials on the surface, and receive serious injury for which you might be liable. A stand-off insulator connects the other end of the resistor to the antenna wire. Two of the most popular of these are the Vee beam and the rhombic antennas. Both forms can be made in either resonant unterminated or nonresonant terminated versions.

      If the radiation angle of the wire is 3, then the appropriate included angle is 2 3. The list below shows the optimum included angles for various wavelength Vee beam antennas. NT 2T 1 90 2 73 3 58 4 50 5 44 6 40 7 36 8 35 Note in the list above that the optimum angle changes on harmonically operated Vee beams. It is common practice to design a Vee beam for a low frequency like the 60, 49, or meter bands and then use it also on higher Maximum frequencies that are harmonics Direction A.

      Vee beam patterns are based on an antenna height that is greater than a half- Figure 7 15 88 a Receiving Antenna Handbook wavelength from the ground. Gain on a Vee beam antenna is about 3 dB higher than the gain of the single-wire longwire antenna of the same size, and is considerably higher than the gain of a dipole see Figure At three wavelengths, for example, the gain is 7 dB over a dipole. One wire of the Vee beam is connected to each conductor of the transmission line. Some books state that the two wires to the receiver are mere downleads, and need not be parallel to each other.

      I doubt that advice, and recommend against it. While open wire transmission line is a tad difficult to work with, it is usually worth it. I he upper Vcc is A. Each wire should be longer than lA. There are two angles present on the rhombic antenna. For transmitting rhombics, the resistor should be capable of dissipating at least one-third the average power of the transmitter.

      For receive-only rhombics, the termination resistor Figure 92 a Receiving Antenna Handbook A variation on the theme is the vertically polarized rhombic of Figure His mission was to listen for amateur radio signals from North America. Godley went to Scotland to see if that could happen The Beverage provides good directivity and good gain, but is not very efficient.

      As a result, it is preferred for receiving but shunned for transmitting. Some attempts have been made at making Beverage antennas work as high as the meter citizens band or the meter ham band Either that, or particular propagation conditions made the antenna work well during the period of the experiment. The experimental results are probably valid, but are misinterpreted.

      These conditions are normal in the AM BCB, where nearly all transmitting antennas are vertically polarized. The polarization of the received signal not only changes in those bands, but does so constantly when conditions are unsettled. It consists of a single conductor 16 to 8 wire, with 14 being most common erected about eight to ten feet above ground. Thus, one source claimed that sand beaches adjacent to 94 a. Figure shows why poorly conductive soil is needed.

      When these signals propagate along the wire, they reach the receiver end essentially out of phase with each other, so they cancel. Thus, the Beverage exhibits very deep nulls off the sides at right angles to the wire. Signals from either direction set up in-phase reinforcing waves at the ends. Signals arriving from the rear direction also build up in- phase reinforcing electrical signals, but these propagate towards the termination resistor end, where they are absorbed by the resistor and therefore lost.

      As with any transmission line, the electrical wave in the wire has a lower velocity of propagation than the electromagnetic EM wave in free space. The velocity factor is sometimes expressed as a decimal such as 0. As noted earlier, all transmission lines have an attribute called characteristic impedance, symbolized by Z Q. On receive antennas, a component of the signal set up in the wire by the electromagnetic wave travels towards the receiver, while another component travels towards the termination. Figure shows curves of impedance vs. Here are the diameters d of several popular U.

      Heigbit Feet Figure Another of the debates found among Beverage fans regards the best length for the antenna. Longwire Antennas r 97 Like the longwire antenna, the Beverage needs a termination resistor that is connected to a good ground. As in the longwire case, insulated or bare wire a quarter-wavelength long makes the best radials. Many articles and books on Beverages show ground rods ol two or three feet long, which borders on the ridiculous. Poor soil requires longer ground rods, on the order of six to eight feet. As before, copperclad steel makes the best rods. In addition to the radials and ground rod, Misek also recommends using a wire connection between the ground connection at the termination resistor and the ground connection at the receiver transformer see again Figure Karl F.

      Computational Electromagnetics and Model-Based Inversion. Elias H. Mingzhong Wu. B Jayant Baliga. Fundamentals of Aperture Antennas and Arrays. Trevor S. Resistive Switching. Daniele Ielmini. Modeling and Simulation for Microelectronic Packaging Assembly. Sheng Liu. Nanopositioning Technologies. Changhai Ru. Jordi Naqui. Vibration Engineering and Technology of Machinery. Jyoti K. Metal Matrix Composites. Vijayan Krishnaraj. Nanowire Transistors. Jean-Pierre Colinge. Nanoelectronic Circuit Design. Deming Chen. Charge-Trapping Non-Volatile Memories.

      Panagiotis Dimitrakis. Vincenzo Pecunia. Jianming Jin. High Temperature Electronics. Patrick McCluskey. Designing Quiet Structures. Gary H. Extremum-Seeking Control and Applications. Chunlei Zhang.