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Transcripts for Mann DX, Page Three |
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Carl Mann DX: Carl Mann of Omaha, Nebraska is a veteran journalist and radio hobbyist. Carl has been introducing KNLS listeners to the world of distance listening (DXing) for more than a decade. You can review Carl's scripts by clicking on the subjects listed above.
Broadcasters are stations intended for reception by the general public. They can be found on Longwave, mediumwave, shortwave, and VHF which covers FM and television. Most Dxers start out by logging broadcasters, with later interest expanding into, or being replaced, by utility and ham stations. Radio began as a communication medium, with two-way communication being the principal use for “wireless” technology. But sending out signals one-way with intentions of a reception-only audience soon developed, and programming for the general public became popular making broadcasting common worldwide. Granted, the term broadcast means to disseminate in all directions and can apply to a communications station. Indeed, the famous broadcast of music and voice to wireless operators from Brant Rock, Massachusetts, in 1906 preceded the golden era of broadcasting by at least ten years. But only stations that seek no radio communication in response and seek a mainstream audience are regarded as broadcasters. The rest are utility stations, designed primarily for two-way communication. There is a gray area where utility stations are allowed to broadcast one-way, though to a much narrower intended user than the general public. Time signal stations such as WWV broadcast their time and frequency standards to anyone who wants to make use of them. Coast Guard stations broadcast weather conditions with no response expected. Even amateur radio operators are allowed to broadcast one-way under certain conditions, such as relaying space shuttle communications for general pickup. Other one-way transmissions include telecommands and telemetry signals, beacon stations, and of course general calls to other stations in trying to establish a contact. But none of these audiences can be called general so they don’t fit the accepted definition of broadcaster.
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The position of a station on a radio dial is determined by its transmitter frequency. The frequency is given in Hertz or in Wavelengths. The frequency is determined by the number of times per second the transmitter’s alternating current in the antenna goes through a cycle of peak positive and peak negative energy. A current reaching these peaks 100 thousand times per second has a frequency of 100 thousand cycles per second. Cycles are called Hertz in radio terms, spelled, capital H-e-r-t-z, so that would be 100 thousand Hertz. And since the prefix for a thousand is called Kilo, that would also be equal to 100 kilohertz. A station on 100 kilohertz is operating in the low radio frequency band called longwave. Putting it in reverse, a station on 5 megahertz has its antenna current reaching positive and negative peaks 5 million times per second. Mega is the prefix for million, so 5 megahertz is the same as 5 million hertz. Time station WWV is found on 5 mHz. In the earlier days of radio the dial position was determined by wavelength instead of frequency. Wavelength is measured in meters. Wavelength is related to frequency; it’s the measurement of how far a radio wave travels at the speed of light before the next radio wave leaves the antenna. At higher frequencies, these waves have a shorter distance in between them. That’s why Meter bands have smaller numbers as the frequency goes up. For example, the 49meter band is around 6 megahertz, while the 31 meter band is around 9 megahertz.
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Call letters are the official identification of licensed stations. The government of the country in which they operate assigns them. Most often a different set of call letters is issued for each assigned transmitter and frequency, but ham operators and many utility stations have the same call letters that can be used on various frequencies. And some operations use the same call simultaneously on different frequencies, such as time station WWV. In some countries the call letters must be announced during hourly station identifications. In other countries they are of secondary importance and only appear on the station’s license. Communications stations, especially amateur radio operators required to use them every ten minutes, use call letters more frequently. The prefix of the call letters, which is the first one or two letters, designates the country in which the transmitter is operating. In the U.S., K and W are used in broadcasting. In communications the U.S. also uses combinations of AA to AZ and NA to NZ for the prefix. Other examples include VE for Canada communications stations while using CB, CJ, CH, and CK for broadcasters. In Mexico, the prefix is XE. In some countries a number following the prefix may be used to designate a district within the country. A chart of call prefixes can be found in radio and amateur radio reference books. Some governments allow the applicant to select their call letters providing the set is not already in use. Shortwave broadcasters in many parts of the world choose not to use their call letters and instead identify with a name or slogan. Many Latin American stations have call letters but only identify by their slogans, such as Radio Mexico International, or Radio Havana. Other still use both, like TIFC, The Lighthouse of the Caribbean, and HCJB the Voice of the Andes. The Voice of America dropped the use of call letters in the 1950s.
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The ionosphere is made up of general layers, each having different characteristics. These layers are not really well-defined but are general regions of the ionosphere where specific behavior towards radio signals take place at various times of the day. The layers vary in height and intensity throughout the 24-hour day. Understanding how each region works will help with the understanding of radio propagation. The layers are identified, in order of altitude, as layers D, E, F1 and F2. The nearest layer to earth’s surface at about 40 miles, D, is present only during direct sunlight and vanishes quickly at your local sunset. It also differs from the other layers because it does not refract radio signals back to earth but instead absorbs them. Lower frequencies are affected the most; at about 7 to 10 mHz, signals begin passing through the D Layer to be refracted downward by the upper layers to be heard at great distances. The next highest layer at about 60 miles is the E layer. Active during the day, the E-layer will refract signals. The E-layer weakens during the night but never completely vanishes. As it weakens, the higher frequency signals will disappear first. But the real workhorses are the F1 and F2 layers at 140 to 200 miles. These can refract signals over the horizon at great distances. At night, the two weaken and merge into one F layer. But like the E layer, it too will last all night. As it weakens overnight, it will begin to allow higher frequency signals to penetrate on out into space rather than refract back to earth. This explains why the 7 to 10 mHz region is a general pivotal point for day and night reception conditions. The D layer and active E and F layers allow high frequency stations to get out during the day, and the absence of the D layer along with a weaker but still present E and F layer region makes for long distance reception at lower frequencies during the night.
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Interference is any signal or noise that disrupts listening to the desired signal. It’s important to know the different types of interference so that it can be reported accurately to the station in reception reports, or so that the sources can be located for possible elimination. Electrical interference can be identified by its sound. Motors create a grinding whir, spark plugs sound like popping that varies with speed, fluorescent lights and dimmers create a hash, thermostats a periodic hash of a minute or so. Computers, television sets and touch controls for lights generate a loud buzz on parts of the bands that appear every 10 to 15 kHz. Local electrical interference is the only kind of interference that a listener may try to locate and eliminate. Using a portable radio tuned to an interfering noise is one way to track down its source. If it’s off your property and can be traced to a faulty power pole transformer or leaky television cable, a call to the power or cable company might get it fixed. If it tracks to a neighbor’s home, only diplomacy can help. Atmospheric interference is static caused by lightning. It’s been on the spectrum since the dawn of time. Each lightning bolt is a high-powered broadband spark transmitter that can be heard thousands of miles away. This kind of interference diminishes as you tune higher in frequency. Interference from other stations is created when they are operating too close or on the same frequency as the desired signal. Co-channel interference is caused by a station on the same frequency as the desired station. Adjacent channel interference is from a station on a nearby frequency that creates splatter from its audio side bands, particularly annoying when music is played. If the stations are not on the exact same frequency but very close to each other, a tone called a heterodyne note is created causing additional interference. For this kind of interference only increased selectivity in receiver design or filters can help.
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The antenna is the essential part of a receiver that captures the radio station’s signal from the air. Some antennas are built into the receivers, but bigger receivers have a jack for connecting an external antenna. The most common external antenna is the random length longwire. Strung as high as possible and kept away from power lines, they perform quite well at all frequencies. A similar antenna called the inverted L allows for a shielded lead-in using coaxial cable to avoid noise pickup from electrical sources as it comes into the building. For higher performance, a dipole antenna may be designed for peak performance on a desired band. A fan-dipole is a series of dipoles with lengths cut at different frequencies all fanning out to their support points from a common lead in. Dipoles also show near-peak performance on harmonics, so a 30-meter dipole will also do well on its sub-harmonic of 60-meters, and a 40-meter ham band dipole also tunes nicely on its harmonic of 20-meters. In locations where an outdoor antenna is not permitted, a hidden indoor antenna can be satisfactory. Also useful for apartments is the active antenna, a small antenna with a broadband amplifier that feeds the receiver. Other antennas include the trapped dipole that has inductance coils at specific points to make a shorter wire perform like a longer wire. These are sold commercially with single antennas designed for multiple bands. Loop antennas are rotatable and directional, but work best at lower frequencies. And for the serious Dxer is the Beverage antenna, a long wire stretching out for a thousand feet or more. Often they are installed at remote sites for Dxpeditions and can snag normally inaudible signals for reception from the direction they are pointing. A device for portable radios is also on the market where the antenna wire is reeled out a short distance and clipped to the antenna lead. But some portables are already designed with such sensitivity that this may cause them to overload or even be damaged, so be cautious.
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Audio is sound, and the range of human hearing is about 20 to 20 thousand cycles per second. An audio signal is an electrical signal operating at a frequency that falls within the range of human hearing when converted by a speaker. While still an electrical signal in various circuits and stages, it’s called A-F for Audio Frequency. If the signal is in the Radio Frequency range, it is called an R-F signal. Some R-F signals such as the transmitter signal contain audio information, but still is regarded as R-F. The fidelity of a receiver describes how faithfully the signal’s quality is restored to what was originally broadcast. A receiver with poor fidelity will only re-create a portion of the audio spectrum that is being broadcast, and as a result music won’t sound full. This can be caused by a narrow bandwidth on the receiver. The bandwidth is the range of audio frequencies from low notes to high notes that is being passed by the circuitry. But full fidelity is not always needed, especially for Dxing or listening to distant broadcasts. Some receivers have a bandpass filter that can be switched in. This filter will intentionally narrow the audio bandwidth and allow only the middle portion of the audio spectrum to come through. Since the human voice falls into this range, it will still be readable, but a lot of other interfering noises will be greatly reduced. The narrower the bandpass, the more highs and lows will be taken out. Audio Distortion occurs when the signal is altered from the original. It can be caused by malfunctioning equipment or by running the audio circuitry too loud. The signal can also become distorted by distance as it travels through the ionosphere one or more times. Other words used to describe a receiver’s audio are: Clean, meaning good fidelity and no distortion or extraneous noises; Bassy, where high notes and sibilant sounds (like S’s and T’s) are missing; and Tinny, with no bass notes or “bottom” to the audio. Some terms describing a transmitter’s audio include: Low audio level, where the signal is good but the sound is weak, and overmodulated, where the sound is loud and distorted.
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While tuning to broadcast stations on shortwave, many other signals in between used for communication purposes will be heard, some of them using code instead of voice to send their messages. Morse Code is a set of dot and dash combinations that represent letter characters, numbers, and punctuation. Samuel Morse, the developer of the telegraph, developed it in the 1800s. The earliest code called American Morse had some characters that differ from today’s International Morse code. It was used for more than a century by railroad and commercial telegraphers. When wireless was developed, International Morse code was used. It is still in use today, although it is fading into history being replaced by machine and computer codes that are much quicker and more error-free. The U.S. Coast Guard stopped using Morse Code in 1995. The oldest and most common method of transmitting Morse Code is Continuous Wave, or CW. These are the dots and dashes heard on the shortwave bands where the transmitter carrier is keyed on and off. No sound is heard unless the carrier is beating against another carrier, either the receiver’s Beat Frequency Oscillator or another nearby station, which give the dots and dashes a tone. Mechanical machines called Teletypes can be used to send and receive code messages, displaying their messages on paper or a computer screen. Abbreviated RTTY, Radio Teletype signals sound like very fast Morse code signals. Many of these stations use Frequency Shift Keying, Abbreviated FSK. This uses two separate frequencies about 10 kHz apart. Rather than turning the transmitter on and off to make up the dots and dashes of the code, the transmitter shifts between two frequencies instead. All US stations are required to use International Morse Code, except for special codes required for telemetry, remote control commands, and digital code understood only by computers.
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A mode is a particular form or variety of doing something. In radio, it’s the form of transmitting information. This will help explain many of those strange sounding signals transmitting in between broadcast stations. They are communication stations in different modes of operation, transmitting text, voice, or images. Once a transmitter is turned on, its silent signal is only an open carrier. But getting the transmitter to send information or have a personality with that carrier requires a mode of operation. The simplest mode is to key the signal on and off in Morse code. This is called Continuous Wave, abbreviated CW. A steady carrier with a tone that is keyed in Morse Code will also work. A very fast keying of the transmitter in a code that can be understood by a machine that types out the copy is Radioteletype, abbreviated the RTTY mode. Or instead of keying the transmitter on and off, the code can be sent by shifting the transmitter frequency back and forth between two channels very close to each other. This is called Frequency Shift Keying, or FSK. Putting sound on the carrier is called modulating the carrier. This can be accomplished through varying either the strength or the frequency of the signal at the corresponding audio frequency of the sound to be transmitted. This is either the AM mode for the former method or FM for the latter. An AM signal with the carrier and one side band removed is in the single side band mode, abbreviated SSB. It is the most efficient method of voice transmission, but makes voices sound muffled until properly tuned in by a receiver that can restore the carrier. Other modes include images, the sending of pictures by Fax, short for Facsimile, and SSTV, which is Slow Scan Television. These signals produce a varying buzzing sound on the normal receiver.
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Signal processing is the manipulation of the received signal so that it may be heard more clearly. It can be processed while still at its radio frequency or as audio. Many accessories are available to the radio listener to help boost the readability of distant signals that are facing interference. Some are built into the more expensive receivers. Most receivers have a tone control to boost or reduce the high and low frequencies. This is a form of signal processing of audio frequencies. Sophisticated tone controls, called equalizer units, can remove some interfering tones and boost the voice range helping clarify reception of stations experiencing interference. Since the voice range falls in the middle of the audio band, most of the information can get through. The most modern of audio signal processing is Digital Signal Processing, abbreviated DSP. The unit will convert the audio into digital information where it can be precisely manipulated then returned to analog for listening. Some of the more expensive receivers have filters that can be switched in to narrow the bandwidth of the received signal, eliminating some nearby interference. Another kind of filter called a notch filter can vary the null point of the filter anywhere within the received bandwidth, thereby reducing interference that is coming in from one particular spot, such as a heterodyne. The QRM Cancellor can reduce electrical interference from lights and motors by setting up a separate receiver on the same frequency and feeding it back into the original receiver at an opposite phase thereby canceling the noise it is picking up. Preselectors and antenna tuners help the signal arrive at the receiver with a better match and more selectivity, thereby increasing the signal and more effectively rejecting neighboring stations. The importance of any additional accessories for your receiver depends on your personal needs. Generally it’s better to buy a receiver with as many features as you need rather than an inexpensive receiver with many additional accessories.
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The New Life Station is pleased to provide transcripts online for a number of KNLS programs. Please note that all scripts are the property of World Christian Broadcasting and/or SeedSower Productions. They are provided here for your personal enjoyment only and may not be disseminated in any fashion without prior written permission.