Broadcasting: Basic Concepts

In order to program a radio station it is important to understand some basic concepts. A programmer may develop an excellent music format only to have it crippled by being placed on an AM station.


Radio transmission is a way of sending messages using radio wave propagation. Before that can happen sound information must be converted into electrical form so that it can be transmitted using electromagnetic energy. The process of turning sound into this form so that it can be transmitted is called transduction.

This involves two steps. First, sound is converted (encoded) into an electrical pattern. Second, the electrical signal travels through a channel that allows the encoded sound to reach a transmission point (transmitter) and then on to a reception point (receiver).

Devises such as CD players, microphones, turntables, and tape recorders (transducers) transform sound from a series of physical vibrations into electrical energy that can then be transmitted. We can imagine electromagnetic energy which includes visible light, infrared radiation and X rays, on a scale from low to high. This energy behaves like light and travels through space at 186,000 miles per second, or 300 million meters per second.

Radio waves, like other waves are measured by frequency, the number of times a wave varies above and below a zero point. This is represented visually by drawing a horizontal line representing zero. The wave can then be represented by drawing a line up (positive) back down through the zero point and down (negative), then back up to the zero point. One such oscillation on either side of zero is called a single cycle. Radio waves oscillate many times per second.

In addition to frequency, radio waves also have amplitude. Amplitude describes the height or intensity of a given wave. The ability to manipulate variations in amplitude and frequency makes possible the transmission of sound.

Types of Stations

Two transmission methods (systems of modulation) used are used. AM amplitude modulation varies the amplitude (intensity) of the carrier, while the frequency remains the same. FM encodes the sound information by changing the frequency, while the amplitude remains constant.

Each system has its advantages and disadvantages. AM is the older of the two transmission systems. FM, the newer system, is now the dominant band. It accounts for more than 75% of radio listeners.

AM's advantage is that it travels great distances, particularly at night via skywave. Its disadvantage is that it has limited frequency response. AM radio is restricted to 10 kilohertz. This limitation gives it less than the full-range of frequencies needed for ideal fidelity. AM stations are restricted from producing sound above 5,000 cycles per second. This results in a loss of the overtones that provide the richness and warmth that give fullness to sound. This further disadvantages AM stations by reducing their dynamic range, the difference in volume from soft to loud sound.

Because AM transmission varies the amplitude of the wave, it is more susceptible to interference. AM stations broadcast using medium frequency (MF) waves. Music has almost disappeared from AM radio. Successful formats include: News, Talk, (Full Service) and Sports.

To the average listener, FM's obvious advantage is stereo. In FM stereo, the right and left channels are transmitted on separate subcarriers. Stereo receivers detect both signals and reproduce right and left channels. The mono signal (combined left and right) leaves the transmitter as a single signal. In addition to stereo, FM benefits from having a wider bandwidth than AM, 200 kilohertz vs 10 kilohertz. This wider bandwidth give FM a frequency response that extends from below 10 Hertz to 15,000 Hertz. As a result the listener hears a truer representation of sound. Most music formats are now heard on FM. Talk and news, formats popular on AM are also heard on FM. WWBD FM, (formerly talk, now '80s format "The Point") Philadelphia and WTOP FM, (news) Washington, DC (WNEW, New York former Rock 'n' Roll Powerhouse is now a talk station as is KLSX in Los Angeles) are examples.

One of FM's other major advantages is a built in resistance to interference. Unlike AM, FM transmission varies the frequency of the signal keeping the amplitude constant. Static interacts with the amplitude of radio waves. This results, in FM being relatively interference free (see No Static At All provided by WCRB FM, Boston.


FM does have disadvantages with respect to AM. It occupies the VHF band. Signals at these higher frequencies attenuate quickly and travel line-of-sight, no further than the horizon.

FM signals are also prone to multipath interference. This happens when a bounced signal interacts with the original signal inside your receiver.

Station Classes

One of the most important things to learn about radio is that not all stations are created equal. According to radio consultant Jay Williams, Jr. "Generally speaking when two stations offer the same format in a like manner that is, comparative execution and performance levels the outlet with the strongest and clearest signal will nearly always garner the largest following" (Keith, 1987).

AM Stations

AM stations are those broadcast stations that occupy the portion of the broadcast spectrum between 535khz - 1705khz.

Classes of AM Stations

§73.21 Classes of AM broadcast channels and stations.

(a) Clear channel. A clear channel is one on which stations are assigned to serve wide areas. These stations are protected from objectionable interference within their primary service areas and, depending on the class of station, their secondary service areas. Stations operating on these channels are classified as follows:

(1) Class A station. A Class A station is an unlimited time station that operates on a clear channel and is designed to render primary and secondary service over an extended area and at relatively long distances from its transmitter. Its primary service area is protected from objectionable interference from other stations on the same and adjacent channels, and its secondary service area is protected from interference from other stations on the same channel. The operating power shall not be less than 10kw nor more than 50 kW.

(2) Class B station. A class B station is an unlimited time station which is designed to render service only over a primary service area Class B stations are authorized to operate with a minimum power of 0.25kw (or, if less than 0.25kw, an equivalent RMS antenna field of at least 141 mV/m at 1 km) and a maximum power of 50kw, or 10kw for stations that are authorized to operate in the 1605-1705kHz band.

(3) Class D station. A class D station operates either daytime, limited time or unlimited time with nighttime power less than 0.25kw (or, if less than 0.25kw and an equivalent RMS antenna field of less than 141 mV/m at one km. Class D stations shall operate with daytime powers not less than 0.25kw nor more than 50kw. Nighttime operations of Class D stations are not afforded protection and must protect all Class A and Class B operations during nighttime hours. New Class D stations that had not been previously licensed as Class B will not be authorized.

(b) Regional Channel. A regional channel is one on which Class B and Class D stations may operate and serve principal center of population and the rural area contiguous thereto.

(c) Local channel. A local channel is one on which stations operate unlimited time and serve primarily a community and the suburban and rural areas immediately contiguous thereto.

(1) Class C station. A Class C station is a station operating on a local channel and is designed to render service only over a primary service area that may be reduced as a consequence of interference in accordance with §73.182. The power shall not be less than 0.25kw, nor more than 1kw. Class C stations that are licensed to operate with 0.1kw may continue to do so.

§73.25 Clear channels: Class A, Class B and Class D stations.

The frequencies in the following tabulations are designated as clear channels and assigned for use by the classes of stations given:

(a) On each of the following channels, one Class A station may be assigned, operating with power of 50kw; 640, 650, 660, 670, 700, 720, 750, 760, 770, 780, 820, 830, 840, 870, 880, 890, 1020, 1030, 1040, 1100, 1120, 1160, 1180, 1200 and 1210 kHz. In Alaska, these frequencies can be used by class A stations subject to the conditions set forth in §73.182(a)(1)(ii). On the channels listed in this paragraph, Class B and Class D stations may be assigned.

(b) to each of the following channels there may be assigned Class A, Class B and Class D stations: 680, 710, 810, 850, 940, 1000, 1060, 1070, 1080, 1090, 1110, 1130, 1140, 1170, 1190, 1500, 1520, 1530, 1540, 1550 and 1560 kHz.

(c) Class A, Class B and Class D stations may be assigned on 540, 690, 730, 740, 800, 860, 900, 990, 110, 1050, 1220, 1540, 1570 and 1580 kHz.

§73.26 Regional channels: Class B and Class D stations.

(a) the following frequencies are designated as regional channels and are assigned for use by Class B and Class D stations: 550, 560, 570, 580, 590, 600, 610, 620, 630, 790, 910, 920, 930, 950, 960, 970, 980, 1150, 1250, 1260, 1270, 1280, 1290, 1300, 1310, 1320, 1330, 1350, 1360, 1370, 1380, 1390, 1410, 1420, 1430, 1440, 1460, 1470, 1480, 1590, 1600, 1610, 1620, 1630, 1640, 1650, 1660, 1670, 1680, 1690 and 1700 kHz.

(b) Additionally, in Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands the frequencies 1230, 1240, 1340, 1400, 1450 and 1490 kHz are designated as Regional channels, and are assigned for use by class B stations. Stations formerly licensed to these channels in those locations class C stations are redesignated as Class B stations.

§73.27 Local channels; Class C stations.

Within the conterminous 48 states, the following frequencies are designated as local channels, and are assigned for use by class C stations: 1230, 1240, 1340, 1400, 1450 and 1490 kHz.

§73.201 Numerical designation of FM broadcast channels.

The FM broadcast band consists of that portion of the radio frequency spectrum between 88 megacycles per second (MHz) and 108 MHz. It is divided into 100 channels of 200 kHz each. For convenience, the frequencies available for FM broadcasting (including those assigned to noncommercial educational broadcasting) are given numerical designations which are shown in the table below:

Note: Channels 201-220 are designated for noncommercial broadcasting only (frequencies between 88 and 92).

Frequency Channel Number Frequency Channel Number
88.1 MHz 201 98.1 MHz 251
88.3 MHz 202 98.3 MHz 252
88.5 MHz 203 98.5 MHz 253
88.7 MHz 204 98.7 MHz 254
88.9 MHz 205 98.9 MHz 255
89.1 MHz 206 99.1 MHz 256
89.3 MHz 207 99.3 MHz 257
89.5 MHz 208 99.5 MHz 258
89.7 MHz 209 99.7 MHz 259
89.9 MHz 210 99.9 MHz 260
90.1 MHz 211 100.1 MHz 261
90.3 MHz 212 100.3 MHz 262
90.5 MHz 213 100.5 MHz 263
90.7 MHz 214 100.7 MHz 264
90.9 MHz 215 100.9 MHz 265
91.1 MHz 216 101.1 MHz 266
91.3 MHz 217 101.3 MHz 267
91.5 MHz 218 101.5 MHz 268
91.7 MHz 219 101.7 MHz 269
91.9 MHz 220 101.9 MHz 270
92.1 MHz 221 102.1 MHz 271
92.3 MHz 222 102.3 MHz 272
92.5 MHz 223 102.5 MHz 273
92.7 MHz 224 102.7 MHz 274
92.9 MHz 225 102.9 MHz 275
93.1 MHz 226 103.1 MHz 276
93.3 MHz 227 103.3 MHz 277
93.5 MHz 228 103.5 MHz 278
93.7 MHz 229 103.7 MHz 279
93.9 MHz 230 103.9 MHz 280
94.1 MHz 231 104.1 MHz 281
94.3 MHz 232 104.3 MHz 282
94.5 MHz 233 104.5 MHz 283
94.7 MHz 234 104.7 MHz 284
94.9 MHz 235 104.9 MHz 285
95.1 MHz 236 105.1 MHz 286
95.3 MHz 237 105.3 MHz 287
95.5 MHz 238 105.5 MHz 288
95.7 MHz 239 105.7 MHz 289
95.9 MHz 240 105.9 MHz 290
96.1 MHz 241 106.1 MHz 291
96.3 MHz 242 106.3 MHz 292
96.5 MHz 243 106.5 MHz 293
96.7 MHz 244 106.7 MHz 294
96.9 MHz 245 106.9 MHz 295
97.1 MHz 246 107.1 MHz 296
97.3 MHz 247 107.3 MHz 297
97.5 MHz 248 107.5 MHz 298
97.7 MHz 249 107.7 MHz 299
97.9 MHz 250 107.9 MHz 300

§73.205 Zones.

For the purpose of allotments and assignments, the United States is divided into three zones as follows:

(a) Zone 1 consists of the portion of the United States located within the confines of the following lines drawn on the United States Alberts Equal area Projection Map (based on the standard parallels 29 1/2 and 45 1/2; North American datum); Beginning at the most easterly point on the State boundary line located at North Latitude 3749' and West Longitude 80 12' 30"; thence westerly along the southern boundary line lines of the States of West Virginia, Ohio, Indiana and Illinois to a point at the junction of the Illinois, Kentucky, and Missouri state boundary lines; thence northerly along the western boundary line of the State of Illinois to a point at the junction of the Illinois, Iowa, and Wisconsin state boundary lines; thence easterly along the northern state boundary line of Illinois to the 90th meridian; thence north along this meridian to the 43.5-parallel; thence east along the parallel to the United states-Canada border; thence southerly and following that border until it again intersects the 43.5 parallel; thence east along this parallel to the 71st meridian; thence in a straight line to the intersection of the 69th meridian and the 45th-parallel; thence east along the 45th parallel to the Atlantic Ocean. When any of the above lines pass through a city, the city shall be considered located in Zone 1. (See Figure of §73.699 [in complete copy of the rules]).

(b) Zone 1A consists of Puerto Rico, the Virgin Islands, and that portion of the State of California which is located south of the 40th parallel.

(c) Zone II consists of Alaska, Hawaii and the rest of the United States which is not located in either Zone I or Zone IA.

§73.210 Station classes.

(a) The rules applicable to a particular station, including minimum and maximum facilities requirements are determined by its class. Possible class designations depend upon the zone in which the station's transmitter is located. The zones are defined in §73.205. Allotted station classes are indicated in the Table of Allotments, §73.202. Class A, B1 and B stations may be authorized in Zones I and I-A. Class A, C3, C2, C1 and C stations may be authorized in Zone II.

§73.211 Power and antenna height requirements.

(a) Minimum requirements.

(1) Except as provided in paragraphs (a)(3) and (b)(2) of this section, FM stations must operate with a minimum effective Radiated power (ERP) as follows:

(i) The minimum ERP for Class A stations is 0.1kw
(ii) The ERP for Class B1 stations must exceed 6kw.
(iii) The ERP for Class B stations must exceed 25kw
(iv) The ERP for Class C3 stations must exceed 6kw.
(v) The ERP for Class C2 stations must exceed 25kw.
(vi) The ERP for Class C1 stations is 100kw.
(vii) The minimum ERP for Class C stations is 100kw.

(2) Class C stations must have an antenna height above average terrain (HAAT) of at least 300 meters (984 feet). No minimum HAAT is specified for Classes A, B1, B, C3, C2, or C1 stations.

Station Class Maximum ERP HAAT Contour

(meters)   (feet)
A 6kw (7.8 dBk) 100   (328) 28
B1 25kw (14.0 dBk) 100 (328) 39
B 50kw (17.0 dBk) 150 (492) 52
C3 25kw (14.0 dBk) 100 (328) 39
C2 50kw (17.0 dBk) 150 (492) 52
C1 100kw 20.0 dBk) 299 (981) 72
C 100kw 20.0 dBk) 600 (1968) 92


Keith, M. C. (1987). Radio programming: Consultancy and Formatics Focal Press: Boston.

O'Donnell, L. M., Hausman, C., Benoit, P. (1989). Radio station operations: Management and employee perspectives. Wadsworth: Belmont, CA.

Keith, M. C. and Krause, J. M. (1989). The Radio Station Focal Press: Boston.

Broadcasting and Cable Yearbook 1997 (1997). R.R. Bowker: New Providence, NJ.

Federal Communications Commission Rules Part 73 (1997). Rules Service Company: Rockville, MD.

Chapter Resource Links

  • Chart of electromagnetic energy.
  • Figure single cycle.
  • AM wave.
  • FM wave.
  • Figure skywave & ground wave.
  • Figure line-of-sight.
  • FigureZone1.
  • WWBD FM Talk radio on FM.
  • WTOP FM News radio on FM.
  • No Static At All provided by WCRB FM, Boston.
  • WMBR at MIT list of radio stations on the World Wide Web.
  • Gebbie Press Radio on the Web
  • BRS Radio Directory
  • Airwaves Journal The radio watcher project.
  • FCC Homepage
  • FCC AM factsheet.
  • AM Stereo FCC explanation of AM stereo.
  • The Basics of AM Radio presented by Radio World.
  • FCC FM factsheet.
  • FCC Conversion converts channel number to FM frequency.
  • FCC Contours contours for FM station classes.
  • FCC Spacing standards for FM station spacing.
  • National Association of Broadcasters
  • Rec.Radio.Broadcasting Usenet newsgroup.
  • Journal of Radio Studies
  • DAB Digital Audio Broadcasting
  • Eureka 147 DAB
  • In-Band On-Channel DAB
  • Lucent Digital Radio
  • USA Digital Radio