Posted-By: auto-faq 184.108.40.206
See reader questions & answers on this topic! - Help others by sharing your knowledge
[Last revised: Oct 3 1993] AM/FM DXing By Scott Fybush and Earl Higgins One of the easiest parts of the radio spectrum to explore are the broadcast bands. This posting will attempt to offer some hints to make your exploration of the mediumwave and VHF-FM bands more enjoyable. I. WHAT ARE THE AM/FM BROADCAST BANDS? The mediumwave (commonly referred to as AM) broadcast band currently extends from 525 to 1605 kilohertz. Channels are spaced in even 10 kHz increments; i.e.: 530, 540, 550, ... , 1600 kHz in the United States and Canada. Elsewhere, channels are spaced in 9 kHz increments, i.e.: 531, 540, 549, etc. In the United States, the band is being expanded to 1700 kHz. Stations which are currently experiencing high levels of interference will begin appearing on the 1610-1700 kHz frequencies sometime in late 1993 or 1994. They will simulcast the new frequencies with the old for a period of a few years, eventually dropping the `old' frequency. This opening up of new channels presents some once-in a lifetime opportunities for the alert mediumwave DXer. The VHF-FM broadcast band in the United States extends from 88 to 108 megahertz. Channels are assigned at 200 kHz increments; i.e.: 88.1, 88.3, 88.5, ... , 107.9. The channels from 88.1 to 91.9 are reserved for noncommercial educational stations. Outside the United States and Canada, the boundaries and channel spacing vary. In Japan, the band starts at 76 MHz. In Western Europe, the band generally runs from 88-108 MHz, but channels can be irregularly spaced, i.e.: 101.25 MHz. II. SIGNAL PROPAGATION The distant stations you are able to receive will depend largely upon signal propagation. This varies depending upon the time of day, the season, and other factors. For mediumwave, the single most important factor for good DX is the time of day. Mediumwave signals almost always get absorbed by the D Layer of the ionosphere during daylight hours. As a result, all mediumwave signals received during midday hours will arrive by ground wave, making reception of signals over a few hundred km/miles away unusual in daylight. At night, however, the ionosphere reflects mediumwave signals, making it possible for signals to be heard at much greater distances, up to a few thousand km/miles, via `skywave'. To a lesser extent, the period up to two hours after local sunrise, and two hours before local sunset, called "Critical Hours", have varying levels of skywave, and also can provide some very unusual reception opportunities for the mediumwave DXer. Reception also tends to be better in winter than in summer, due to lower levels of atmospheric noise and longer hours of darkness. In the United States, due to the large number of stations, many smaller mediumwave stations are required to sign off or reduce power sharply at sunset so as to reduce interference to distant stations. Whereas the mediumwave band can be counted on to provide distant reception with much dependability, this is not the case at all on the VHF-FM band. Under `normal' conditions, VHF-FM signals generally carry no more than 150-250 km (100-150 miles), or `line of sight', since the ionosphere generally does not reflect VHF-FM signals. VHF-FM transmitting antennas are thus usually located as high as possible. Tall towers, high buildings, and mountaintops are common VHF-FM transmitter sites. However, under certain rare conditions, the atmosphere will even reflect VHF-FM signals, thus making it possible to receive these stations at quite long distances. There are two major forms this distant reception can take; the most common is Tropospheric Ducting, or tropo for short. Typically, this occurs when a warm air mass forms on top of a cooler mass closer to the ground. The area between these masses acts like a pipe, `bending' the signals back to the earth well beyond the horizon. This reception is most common in local late spring and summer months, in the post-sunrise hours. It will enable the alert VHF-FM DXer to log stations up to 800 km (500 miles) away in optimum conditions. The other relatively widespread form of VHF-FM DX is called Sporadic E, or E-skip, because it is the E Layer of the ionosphere which reflects the signals. Like the name implies, this form of propogation is very sporadic, yet very intense. When it's in, it is VERY strong. Stations from a relatively limited geographic area 1300-2000 km (800 to 1200 miles) away will suddenly boom in, strong, often in stereo but quite fadey, even overpowering semilocals in many cases. It will start at the bottom of the VHF-FM Band (actually TV channels 2-6 first) and work its way up in frequency. The highest frequency at which signals are reflected by the ionosphere is called the Maximum Usable Freqiuency (MUF), just as it is in shortwave, and it can occassionally surpass the top of the VHF-FM dial in an unusually good opening. III. RECEIVERS Almost any radio is capable of some broadcast-band DXing, especially long-distance mediumwave reception. However, most recent radios, even those designed for quality shortwave reception, do not have outstanding broadcast band reception. One exception is the General Electric Superadio III (Model 7-2887.) The SR III is designed for optimum AM/FM broadcast performance, incorporating: * RF amplifiers on both bands * Ceramic filters and Automatic Frequency Control on FM * No PLLs or digital displays for less electronic noise * A 2-way speaker system with 1 watt of audio power The SR III is a bulky (4" x 10" x 12") portable radio which can be run off 120V AC or 6 "D" batteries, providing over 400 hours of battery life. This radio has become popular among the DX community for its exceptional performance. It costs between thirty and sixty dollars in the US, and may be found at many discount outlets. It can be obtained from Bennett Brothers (Order #R3116) at 1-800-621-2626 or 1-800-631-3838, or from Best Products (Order # 140457) at 1-800-950-2398. If you don't have a Superadio, some important things to seek out in a receiver are: * External antenna connections. These make it easier to use a better antenna than the one supplied with the radio. * High selectivity. This refers to the receiver's ability to reject strong signals on adjacent frequencies, and is more important to good reception than is sensitivity, since a good antenna will provide more-than-adequate signal strengths. * Digital frequency display. While the circuitry involved can add to the level of internal electronic noise in the radio, digital display makes it possible to more easily determine what station is being heard. IV. ANTENNAS For mediumwave reception, most receivers have a short internal ferrite rod. This will provide acceptable signals for high-powered distant stations. Ferrite rods are quite directional, and the radio can thus be turned to null out strong interfering signals, or to improve reception of the desired signal. For more advanced DXing, external antennas offer certain advantages. The most common external antenna is a simple random wire, 15m (50 feet) or more run out the window and then as high as possible (up in a tree, for example). The wire can be connected to the external antenna terminal. If none exists, you can open up the radio and wrap the wire a few turns around the ferrite rod inside. It is also possible, although less desirable, to simply wrap the wire around the entire radio. If the radio has a terminal marked "ground" or "GND," another wire can be run from this terminal to a copper rod driven a meter/a few feet into the earth. One problem with a random wire antenna for mediumwave work is it's inability to reject strong local signals. Most receivers today lack the dynamic range to effectively deal with the extremely strong signals from a local mediumwave broadcaster as picked up by a random wire antenna. Thus, some sort of tuned antenna is best for all but the most isolated, rural locations. The most popular antenna for mediumwave DX today is called a `loop' antenna, and can be either of two types: ferrite rod or air-core wound wire loop. These antennas are small, 25-100 cm (1-3 feet) in diameter, and sit on the DXers desk or shack table where they can be easily turned by hand for optimum peak or null of a signal. Each design works with a tuned circuit before feeding the signal into your receiver, and usually this circuit includes a small powered amplifier. Generally speaking, the longer the ferrite rod, or the larger the diameter of the aircore loop, (to a point), the sharper the null of the antenna. 45 to 55 cm (18 to 22 inches) would be optimum for a ferrite rod antenna. Air-core loops need to be made by hand, as there are none on the market. Ferrite loops, however, are available commercially from at least two manufacturers; Palomar Engineers and Radio West. Unfortunately, these two antennas do not have very long ferrite elements; and reviews of their performance in the mediumwave press tends to be mixed. Ideally, one would build their own antenna, or try to find either a used, older Radio West loop or Space Magnet antenna, both pre-1980. Plans for building all sorts of mediumwave loop antennas are available through National Radio Club publications. The address is found later in this FAQ. A more advanced antenna is the "beverage" antenna. This is a length of wire 300 m (1000 feet) or more, with extremely high gain and narrow-beam directional characteristics. It is usually, but not always, terminated at the far end with a 450 ohm resistor connected to a metal stake driven into the ground. It should be pointed in the direction of the desired station. The beverage antenna can, under good conditions, be used for transatlantic and transpacific DX. For VHF-FM, the important factor is height. The higher one can place an antenna, the better reception will be. A multielement Yagi antenna, which can be found in Radio Shack or similar stores, will often produce excellent reception. Since a yagi is quite directional, the use of a rotor is essential for reception of stations in different directions. V. WHAT'S OUT THERE TO LISTEN TO? There are over 10,000 radio stations in the United States alone. It's important to have some idea of what to expect to hear. A good directory is important (see STATION LISTINGS below), but it's essential to know what the station information means. For mediumwave, North American frequencies fall into three basic classes: * CLEAR CHANNEL: These frequencies are 540, 640-780, 800-900, 940, 990-1140, 1160-1220, and 1500-1580 kHz. Clear channels are home to one or two 50,000 watt powerhouse signals which can be heard reliably in half the country or more. Other stations also occupy the clear channels, frequently using less than 1000 watts and very restrictive antenna patterns. In recent years, the US FCC has added many more low power stations to the clear channels, making reception of the big, primary, stations more inteference prone than it once was, but providing excellent hunting for the serious mediumwave DXer. Also, the clear channels are the primary hunting area for Latin American DX due to the relatively small number of North American stations on them. * LOCAL: These frequencies are 1230, 1240, 1340, 1400, 1450, and 1490 kHz, and are sometimes referred to as the 'graveyard' channels by DXers. Stations on local channels can use a maximum of 1000 watts (somewhat higher outside the US). At night, these six frequencies tend to become chaotic, as the hundred-plus stations on each channel cause each other tremendous interference. Although the primary service area of these stations may be twenty miles or less, these stations have been known to reach well over a thousand miles under good conditions. Identifying distant stations on these channels requires a directional antenna, a good ear, and plenty of patience. The National Radio Club keeps distance records for all of the stations on these channels and publishes them in their bulletin, _DX_News_, regularly. * REGIONAL: These are all the remaining channels, including the expanded band frequencies of 1610-1700 kHz. U.S. stations on these frequencies tend to be restricted to 5000 watts, although a recently signed international treaty allows for the possibility of 10,000 or even 50,000 watt stations on these frequencies if they do not interfere with other stations. In practice, only Canada has yet assigned high power stations on these frequencies. While not as noisy as the locals, reception on regional channels can be quite interference prone, with a listener able to identify three or four stations coming in simultaneously on one frequency. Most regional, or class III stations, use directional antennas to reduce interference with distant stations. On VHF-FM, the American FCC has reduced its restrictions on power and antenna height considerably. Today, VHF-FM stations are allowed up to 50,000 watts from a 150 meter antenna in the Northeast and California; 100,000 watts from a 610 meter antenna elsewhere. Many stations, however, serve much smaller areas. These "Class A" stations use only 6000 watts or less. They were formerly restricted to just the following frequencies: 92.1, 92.7, 93.5, 94.3, 95.3, 95.9, 96.7, 97.7, 98.3, 99.3, 100.1, 100.9, 101.7, 102.3, 103.1, 103.9, 104.9, 105.5, 106.3, and 107.1 MHz. While the FCC no longer restricts class A stations to those frequencies, most are still found there. Likewise, only a few of the high-power stations are found on the old class A channels. For stations with extemely high antenna, the FCC mandates that transmitter power be reduced proportionately; thus a station with only 430 watts from a 220 meter antenna will reach about as far as a 3000 watt signal from the usual 91 meter antenna will. VI. TIPS FOR BEGINNING The most important element for beginning DXers is to get to know the dial. Spend a few hours scanning up and down the dial both during the day and at night. At night, many of the clear-channel 50kw stations, particularly the non-directional ones, should be easy to hear. Learn all the local stations. Find out which ones sign off at sunset, which ones go off late at night, and which stay on all night. This will affect which distant stations can be received. If you have a local station on all night, you shouldn't expect to hear another station on that frequency without some tedious nulling. Experiment with radio placement. As you slowly turn the radio, observe its directional characteristics. The Superadio III will receive signals coming from the front and back of the set the best, and attenuate the signals coming in `off the side' of the set. You can use this to your advantage and log several stations on a single frequency. By all means, keep a log of all new stations you hear; someday you'll be glad you did! Better yet, keep it on the computer; that way you can share it with others on the net. After a few months of listening; you should have a list of 200-300 stations you've heard. Most of these will be your `regulars', audible almost daily. Beyond that, you can hunt for the rarer stuff. Try for all 50 US states (very, very difficult), or 20 countries (fairly easy in most locations). Within a few years, you'll likely have heard a thousand or so stations and have a very interesting logbook. Here's a `beginner's target list' of widely heard clear channel AM stations to start you out; from most locations in North America you should be able to hear all but four or five of these fairly easily. 540 CBK Canada SA Watrous 840 WHAS USA KY Louisville 540 XEWA Mexico SL Rio Verde 850 KOA USA CO Denver 640 KFI USA CA Los Angeles 860 CJBC Canada ON Toronto 650 WSM USA TN Nashville 870 WWL USA LA New Orleans 660 WFAN USA NY New York 880 WCBS USA NY New York 670 WMAQ USA IL Chicago 890 WLS USA IL Chicago 680 KNBR USA CA San Francisco 900 XEW Mexico DF Mexico City 700 WLW USA OH Cincinnati 990 CBW Canada MB Winnipeg 720 WGN USA IL Chicago 1020 KDKA USA PA Pittsburgh 730 XEX Mexico DF Mexico City 1030 WBZ USA MA Boston 740 CBL Canada ON Toronto 1040 WHO USA IA Des Moines 750 WSB USA GA Atlanta 1070 CBA Canada NB Moncton 760 WJR USA MI Detroit 1070 KNX USA CA Los Angeles 770 WABC USA NY New York 1100 WWWE USA OH Cleveland 780 WBBM USA IL Chicago 1120 KMOX USA MO Saint Louis 800 PJB Neth Ant. Bonaire 1160 KSL USA UT Salt Lake City 800 XEROK Mexico CH Juarez 1180 WHAM USA NY Rochester 810 WGY USA NY Schenectady 1200 WOAI USA TX San Antonio 820 WBAP USA TX Fort Worth 1210 WOGL USA PA Philadelphia 830 WCCO USA MN Minneapolis VII. SOME ADVANCED IDEAS Once you've mastered the basics, here are some suggestions for areas of specialty DX: * QSLing: Since broadcasters by and large don't use the "Q-codes" so popular in Ham and shortwave DX, QSLs are called `veries' or verification letters by mediumwave and VHF-FM DXers. You'll probably have to send a letter to the station's chief engineer (names of actual verification signers can be found in the NRC AM Log). Expect verification in card form from the 50kw AM stations, and verification letters from just about everybody else. Small stations are often excited to find out they've been heard thousands of miles away, but you'll need to take special care to explain to them exactly what you want as they are likely to not know what a `verie' is. Also, remember to always include return postage with your request. * DX Tests. A few stations still run special DX tests, usually arranged for either The NRC or The IRCA (International Radio Club of America) and published in advance in their respective bulletins (another reason to join!). In the past year alone, the following outstanding feats were accomplished via DX Tests: Hawaii (KUAI-720) was heard as far away as Ontario and Pennsylvania; New Jersey (via WJIC-1510) made it west of the Mississippi; and New Mexico (KHAC-880) made it to the East Coast! These are all fairly difficult states for most DXers (unless, of course, you happen to live in or near them). * Equipment Tests: Some stations run experimental tests with their daytime power after local midnight, in accordance with US FCC and Canadian CRTC rules. Often these will be late Sunday night/Monday morning, when some stations sign off for maintenance (although not as many as used to do so). For example, in Chicago Illinois, many DXers have logged KOMO-1000 from Seattle Washington, testing when Chicago local WLUP goes off on Monday mornings; thankfully Monday mornings just happen to be the time when KOMO seems to like to test with their non-directional day pattern. This makes an otherwise almost impossible state relatively easy around the midwestern US. * Sunrise/sunset DXing. Lots of interesting mediumwave DX can be had when your receiving station and/or the transmitter are in only partial darkness. It's possible to hear distant daytime-only stations this way. This requires a lot of skill, since there may be only ten or fifteen minutes in which to try. In fact most mediumwave DXers log the greatest number of stations in the hour or two right around local sunset, especially in the Fall and Winter months. Don't be surprised if, say, tiny KOKB in Blackwell, Oklahoma blasts right through CBJ and other East Coast powerhouse stations on 1580, for a few minutes right around Blackwell sunset! Anything can happen in the turbulent sunset and sunrise hours. * Transatlantic/Transpacific DX. Some DXers in North America specialize in trying to receive signals on the mediumwave band from across the ocean. This requires outstanding propagation characteristics and plenty of patience (a nice, quiet coastal location can yield some amazing results). * FM Subcarriers and Stereo. VHF-FM stations are allowed to transmit separate programming on a subcarrier. This requires a special decoder (one source is Bruce Elving's FM Atlas; see address below.) FM stations use their SCA (Secondary Communications Authority) subcarriers for transmitting data, background music, ethnic programming, and more. Some AM stations now transmit in stereo. With an AM stereo receiver, you can hear stereo signals from thousands of miles away. * Meteor Scatter. The most masochistic of all VHF-FM DXers attempt to hear VHF-FM signals reflected from --yes, it's true-- meteors in the atmosphere. These DXers learn to identify stations on the basis of a few seconds' listening. VIII. IDENTIFYING YOUR CATCH Radio stations in the United States are required to identify with their full call letters and city of license once an hour, between 10 minutes before and 10 minutes after the top of the hour. Canadian stations are never required to identify, and many never use any identifier other than "Q107" or "Toronto's 590 AM." It's therefore important to use other clues: * Time announcements. These can tell you at least what time zone a station is in. If there's only one or two stations on a frequency in a given time zone, this makes identification easier. * Format. If you have a list of stations that includes formats, use it. That includes knowing what network a station uses, whether the station uses a satellite-delivered music format, what slogans the station might use, etc. * Local color. You might be able to hear names of cities or streets or notable local personalities mentioned during commercials, newscasts, talk shows, or weather forecasts. If the announcer says, "Here's the weather for the beaches today...", the station you're hearing probably isn't in North Dakota (although note, interestingly, there IS a TOWN called Beach, North Dakota; go figure). Likewise, if the forecast is snow flurries and six degrees, you're probably not hearing Miami. These clues are among the most valuable. IX. STATION LISTINGS An essential tool for any DXer is a good station listing. This will help identify what's being received, as well as provide a way to contact the station being heard. For North American AM stations, one essential tool is The NRC AM Radio Logbook, now in its 13th Edition. It includes day and night antenna and power information, format, hours of operation, address, verie signers, network affiliations, etc. Price is $19.95 for US, $20.95 for Canadian, three dollars cheaper for NRC Members. To order write NRC Publications, Box 164, Mannsville NY 13661-0164 USA. NRC also publishes FM and TV Logs. To become a member (highly recommended) and receive a year's worth of `DX News', send $24.00 for US, $25.00 for Canadian to: NRC Subscription Center, Box 118, Poquonock, CT 06064-0118 USA. All other countries, write for price information. Another concise and inexpensive directory is the M Street Radio Directory, published annually. The M Street listing includes frequency, power, directionality, format, address, phone number, and other listings less important to DXing. M Street also is indexed by call letter order and by frequency. The M Street directory costs $29.95 + p/h. It can be purchased directly from M Street at 800-248-4242 or +1 212 473 4668 voice, or +1 212 473 4626 fax. The address is M Street Corp., 304 Park Ave S Floor 7, New York, NY 10010 USA. Another guide for VHF-FM DXers is Bruce Elving's annual FM Atlas. This includes maps showing every VHF-FM transmitter in North America, plus listings by state and frequency indicating power, stereo status, format, subcarriers, and slogans. FM Atlas does not include addresses or phone numbers. It can be purchased directly from Bruce Elving, PO Box 336, Esko MN 55733-0336. It costs $10.95 + $1.05 p/h. Another listing is the Broadcasting Yearbook, which is available at some larger libraries. The Canadian Almanac and Directory includes call letters, frequency, and addresses for Canadian stations. For listings outside North America, consult the World Radio TV handbook, published annually and available through your local bookstore or radio specialty mail order outlets such as the Radio Collection and CRB Publishing. X. CONCLUSION Broadcast band DXing is an exciting way to hear the sounds of cities and towns around the nation and even around the world. It doesn't require hundreds of dollars of expensive equipment or huge antennas on the roof. All it asks of the would-be DXer is time, patience, and knowledge. Have fun! THANKS TO... Bob Foxworth, Garret W. Gengler (antenna ideas), Bob Parnass, Paul Schleck (Superadio information), and Bruce Werner, along with anyone else I may have forgotten. Scott Fybush -- email@example.com Earl Higgins -- firstname.lastname@example.org -- Ralph Brandi email@example.com att!mtunp!ralph Stay idiot-proof. --Log, "Idiot Proof"