Radio antenna

“ For lower frequencies the radiation of a radio signal takes place by interaction between the antenna and the ground. For a vertical antenna, efficiency increases with greater length of the antenna. For a horizontal antenna, efficiency increases with greater distance between antenna and ground. Near-maximum efficiency is attained when this distance is one-half wavelength. This is the reason for elevating low frequency antennas to great heights. ”

“ The signal which radiates out from the transmitting antenna carries all the little variations in pitch and loudness of the human voice. When this signal reaches the distant antenna it establishes in that antenna circuit a current of high frequency which has just the same variations as did the current in the antenna at the sending station. The human voice isn’t there. ”

“ The antenna system is designed to provide reliable above-ground communication. A variable attenuator is connected to the above-ground antenna coax to limit above-ground RTMN radiation to a minimum of 2,000 feet without interfering with RTMN transmissions at other launch complexes. The below-ground antenna branch is a continuous coaxial slotted cable which is routed from the base station radio equipment bay in the control center throughout the under-ground launch complex. ”

“ Depending on the antenna design, the main lobe of a directional antenna can cover 60 degrees or more or be a narrow pencil beam. Directional antennas are used on long-range point-to-point circuits where the concentrated radio energy is needed for circuit reliability. Directional antennas are difficult for the enemy to find the direction of transmission. ”

“ A directional antenna has a single large lobe of radio energy in one direction (Figure D-8) . It is much like a bidirectional antenna with one of its lobes cut off. Several bidirectional antennas (long-wire, sloping-Vee) are made directional by adding a terminating resistor that absorbs the second main lobe. A terminating resistor matches the antenna. A terminating resistor must be able to absorb one-half the power output of the connected transmitter and provide 400 to 600 ohms of resistance. A directional antenna concentrates almost all the radio signal in one specific direction ”

“ Patch asked in amazement.
“That’s the antenna for the transmitter, isn’t it, Mac?” Garry asked.
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Mac nodded. “That long ropelike thing is hollow, and the antenna is in the middle of it. Captain Eaton released a switch that caused the casing to fill with compressed air, and that is what keeps it extended into the sky. That gives us a much better antenna than we could possibly have in here. Also, being as tall as it is, the radio waves leaving it can travel great distances and cross high places which they could not do if it were short. Understand?” ”

“ Because the radio signal travels in the air, any obstruction (such as a mountain) between the antennas can block or reduce the signal. For an antenna 10 feet above the ground, 8 kilometers (5 miles) is the maximum line-of-sight distance. (2) The reflected wave reflects off the earth in going from the transmitting antenna to the receiving antenna. Together, the reflected wave and the direct wave are called the space wave. (3) The surface wave travels along the surface of the earth. It is the usual means of ground-wave communication. ”

“ If the radio signal having a frequency above the critical frequency is sent at an angle, the signal is bent back to earth instead of passing through the region. This can be compared to skipping stones across a pond. If a stone is thrown straight down at the water, it penetrates the surface. If a stone is thrown at an angle to the pond, the stone skips across the pond. For every circuit, there is an optimum angle above the horizon called the takeoff angle. It produces the strongest signal at the receiving station. This optimum takeoff angle is used to select the antenna for a specific circuit. ”

“ In any system of radio-telephony you will always find that there is produced at the transmitting station a high-frequency alternating current and that this current flows in a tuned circuit one part of which is the condenser formed by the antenna and the ground (or something which acts like a ground) . This high-frequency current, or radio-current, as we usually say, is varied in its strength. It is varied in conformity with the human voice. If the human 147voice speaking into the transmitter is low pitched there are slow variations in the intensity of the radio current. ”

“ The effective part of the antenna is a copper wire from which the radio waves are radiated, supported on towers or poles at a height above the ground depending on the wave length used. The wire may be parallel with the earth, or vertical, or arranged at an angle, depending upon the function to be performed. ”

“ RADIATION RESISTANCE—The resistance, which if inserted in place of an antenna, would consume the same amount of power as that radiated by the antenna.
RADIO FREQUENCIES—Electromagnetic frequencies that fall between 3 kilohertz and 300 gigahertz and are used for radio communications.
RADIO HORIZON—The boundary beyond the natural horizon in which radio waves cannot be propagated over the earth’s surface.
RADIO WAVE— (1) A form of radiant energy that can neither be seen nor felt; (2) An electromagnetic wave generated by a transmitter. ”

“ Electromechanical protection circuits ensure that a transmitter can only be connected to an antenna that is tuned to the same frequency. The change of antennas and transmitting frequencies is made during the ten-minute interval between programmes, which always begin on the hour, preceded by the now familiar signature tune of a shepherd playing his flute with the tinkling of sheep-bells in the background, recorded in 1936, followed by the Greek National Anthem. ”

“ This concentration of energy provides a maximum amount of energy to be reflected off of a target, making detection of the target much more probable.
How does the parabolic reflector focus the radio waves? Radio waves behave much as light waves do. Microwaves travel in straight lines as do light rays. They may be focused or reflected, just as light rays may be. In figure 2-40, a point-radiation source is placed at the focal point F. The field leaves this antenna with a spherical wavefront. ”

“ Sky-wave propagation makes the selection of an antenna more complex. The first step is to find the distance between radio stations so that the required takeoff angle can be determined. The takeoff angle versus the distance tables gives approximate takeoff angles for day and night sky-wave propagation. If the circuit distance is 966 kilometers (600 miles) during the day, the required takeoff angle is about 25 degrees. At night, it is 40 degrees. Therefore, the operator selects an antenna that has high gain from 25 to 40 degrees. ”

“ In an emergency, any wire of sufficient length can be used for an antenna; for example, barbed wire, electrical wire, fence wire, and metal-cored clothesline. Communication has been successful using metal house gutters and even metal bed springs. A radio operator's mission is not completed until communication is established. f. Grounding. A good electrical ground is needed for two reasons: first, to protect the operator and his equipment; and second, as a radio frequency ground needed by some antennas to function properly. ”

“ Each antenna consists of two curtains with a total of 8 horizontal dipoles. The dipoles are all fed by open wire feeders which can be remotely switched to enable radiation in two directions 180 degrees apart. There are also three curtains for the 11 metre band (26 MHz) which may be put into service during sunspot cycle 22 if the M.U.F. allows it. ”

“ A TRANSMISSION LINE is a device designed to guide electrical energy from one point to another. It is used, for example, to transfer the output rf energy of a transmitter to an antenna. This energy will not travel through normal electrical wire without great losses. Although the antenna can be connected directly to the transmitter, the antenna is usually located some distance away from the transmitter. On board ship, the transmitter is located inside a radio room, and its associated antenna is mounted on a mast. A transmission line is used to connect the transmitter and the antenna. ”

“ The signal keeps on going through the ether until it strikes that other antenna. Then it climbs along it until it reaches the receiving set and registers the same kind of dot or dash as the one I made at this end. It’s like the pitcher and catcher of a baseball battery. One pitches the ball and the other receives the same ball. ”

“ I told him about my visitor and the repair job. "What I did was add a modulator-oscillator-power amplifier, and a few feet of wire for an antenna, coiled around inside the case."
"So what does that make it?"
"Simple. It makes it a radio transmitter. Not only will he hear what the horses are saying, but anyone in town with a radio tuned to that frequency will, too."
"And where does that get you?" The sergeant was still puzzled but not bored now. ”

“ Small aircraft and small vessels can be detected by an ingenious method, only when they move. This is how it is done:
At the receiving site of the ROTHR system a very large antenna stretches out over a distance of 8,400 feet. It consists of 372 dual-monopole vertical elements each 19 feet high, backed by a huge reflector screen which makes the antenna substantially unidirectional. Each pair of vertical elements has its own receiver which digitizes the incoming signals. All the digitized signals are then fed through a fibre-optic link to a master signal processor. ”

“ A radio astronomy antenna is sensitive to a range of directions typically a few degrees across — the ‘main beam’ — but also has reduced sensitivity in very different directions — the “sidelobes”. Likewise the satellite antenna emits most of its power in a main beam, but also some in sidelobes. The worst effects, which can potentially damage sensitive electronic receiver systems, are for an alignment between the astronomical and satellite main beams — this rules out radio observations close to GSO targets, and should be avoided even for fast-moving LEO satellites. ”

“ Components of a radio transmitter.
1017. Receivers When a radio wave passes a conductor, a current is induced in that conductor. A radio receiver is a device which senses the power thus generated in an antenna, and transforms it into usable form. It is able to select signals of a single frequency (actually a narrow band of frequencies) from among the many which may reach the receiving antenna. The receiver is able to demodulate the signal and provide adequate amplification. The output of a receiver may be presented audibly by earphones or loudspeaker ”

“ Along-wire antenna is made directional by placing a terminating resistor at the distant station end of the antenna. The terminating resistor should be a 600-ohm noninductive resistor capable of absorbing at least one-half of the transmitter power. Terminating resistors are part of some radio sets. They can also be locally made, using supply system parts (National Stock Number 5905-00-764-5573, 100-watt, 106-ohm resistor) . (2) Building a long-wire antenna only requires wire, support poles, insulators, and a terminating resistor (if directionality is desired) . ”

“ In almost the same way that a large truck can carry a bigger load than a small one, the greater number of cycles per second in a high frequency wave permits it to carry more information than a low frequency wave.
However, high frequencies must be generated in different ways than low frequency waves are; they require special equipment to handle them. Radio waves are transmitted by causing masses of free electrons to oscillate or swing back and forth in the transmitting antenna. (Any time electrons are made to change their speed or direction they radiate electromagnetic energy.) ”

“ Inside was a complete radio receiving set, with vacuum tube detector and batteries in perfect working order. Between the roots of the tree an 182 iron pipe had been driven into the earth to act as a ground. The antenna was strung from top to bottom of the tree on the side away from the path, and there was nothing to differentiate the box from an ordinary wire telephone set, except that it was slightly larger. ”

“ Also, the radio operator considers the following:
Always use a resonant antenna if possible to communicate. Always try to use a directional antenna. Remember that WD-1 is insulated, but not shielded. Using it as a lead-in wire to the antenna causes it to lose signal strength before it reaches the antenna. b. The COB or DOB is the primary link between the deployed teams and corps or division G2. COB or DOB stations are normally located well within the security umbrella of the corps or division main and should be close enough to the G2 section to facilitate a wire line for reporting purposes. ”

“ An LRS team that can see everything and report nothing is useless. LRSUs normally use high-frequent radios to report information and receive instructions. Because of the complex nature of using the HF radio spectrum, a LRSU radio operator must have an in-depth knowledge of radios, antennas, and radio wave propagation.
D-1. HIGH-FREQUENCY RADIO FUNDAMENTALS For successful communication, HF radio performance depends on the type of emission (voice or burst device) , transmitter power output, and type of antenna. The challenge facing HF radio operators is tremendous. ”