On The Art of NDB DXing
by Sheldon Remington
© 1989
All Rights Reserved
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Chapter Twelve: The Time Domain
Part One - Idents and Formats Having discussed the spectral or frequency domain of NDB transmissions, let's proceed to the other half: the time domain. This general topic includes any transmitted characteristics which vary as a function of time, and can be divided into two main areas: the keying modulation, and on-air schedule variations. The Morse Code All NDBs identify themselves by transmitting letters, and sometimes numerals, in the International Morse Code, also known as the Continental Code, Radiotelegraph Code, or simply the Morse Code. Other telegraph languages, notably the American Morse Code, have been used in the past but are now obsolete. For a fascinating history of telegraphy see Morse Code: The Essential Language ($5.00 from ARRL), written by LWCA's own L. Peter Carron. Morse Code is a binary language, meaning it consists of on-off keying, and it's the only one designed for direct decoding by the most sophisticated signal processor in existence, the human brain. Unlike the codes used by teleprinters and computer modems, Morse consists of elements of unequal length. The basic timing unit is the length of the dot; the dash is three times the duration of the dot. The space between dots and dashes within a letter or numeral is equal to one dot-length; the space between letters or numerals is normally equal to three dot-lengths. Below is a table showing the combinations for the 26 English-language letters and the 10 numerals.
There are four additional characters which don't have English-language
counter- parts but are used in some NDB idents, mostly in the USSR, but
also by a few US marine NDBS. Since standard typewriters don't have
Cyrillic characters for these, they are normally designated by two English
letters whose Morse elements, when com- bined, equal the special Morse
character, and a line is then drawn over these letters. For example, the
'dash-dash-dash-dash' character is written
We now have a complete set of 40 characters which are used in NDB idents. Note that while it is possible for the beginning NDB DXer to translate identifiers by looking them up in these tables, it is better to commit the Morse Code to memory. Indeed, those who spend substantial time OXing NDBs will eventually find that they've memorized it without deliberate effort, and could then use such knowledge to pass the code test for a Novice or Technician ham license. However, there is a hidden trap here: learning code by use of a look-up table mires us in a roundabout process, first translating the sound into visual dots/dashes, then translating these into English letters. This writer, and many others, found it impossible to increase our code speed above about 8 WPM until we unlearned this two-step process, and starting over, using a direct translation of the rhythmic sound of Morse into English. Peter's book discusses the best ways for learning the code; many aids are available to make the process painless, such as special tapes, computer software, and automatic keyers. NDB Identifiers The choice of the one, two, or three characters for use with a particular NDB's ident does not follow the usual ITU prefix/suffix callsign method. The choice belongs to each country's central government and may not adhere to a precisely organized scheme. Here are some apparent schemes currently in use:
Ident Problems In general, the Beacon Guide, the 'Lost and Found' column, the Radio Beacon Handbook, and other official-data-based listings can be counted on for the correct location of any received ident. However, as with frequency data, an occasional screw-up may occur. These are not the fault of the list compilers; they are caused either by a glitch in the governmental paper-shuffling process, or by an error in equipment set-up by the NDB installer. The result is the "wrong-ident" problem. Some examples from recent years: old IGM-266 Kingman, Arizona, IDing as KGM; IZA-394 Santa Ynez, California, lding as L47 (which is the airport code) and causing a lot of consternation among DXers; PWY-239 Hebronville, Texas, IDing as PYW for several years before being fixed recently; and AVZ-299 Terrell. Texas, initially IDing as ANZ when it came on the air in 1987. Another class of ident defect is the inevitable breakdown in equipment, sometimes unnoticed by the maintenance crew if subtle. Sometimes this will be simple and stable, as when GOL-396 Gold Beach, Oregon, transmitted a clear GOA for a couple of months, or when EMC-375 Winnemucca, Nevada, occasionally lapses into an EAC phase, or when FNM-338 Fort Morgan, Colorado, sends CMM. Other broken idents will mutate in a seemingly-random, continuously-varying way. This was the case with XFK295 La Paz, Mexico, on several occasions, sending '... XRA, URA, XFA, URU, XFU ...etc., and also with the old unsolved unIO XSK-240 and the more recent unsolved IZT 400. These cases can result in erroneous loggings since eventually the defect may cause the ident to resemble desired ones listed around that frequency. This is one of many reasons why logging a beacon should always require hearing or taping several repetitions of the ldent, not just one. On a related note. be cautious of the missing-dot syndrome. Since a dash has thrice the duration of a dot, dots are much more likely to be wiped out by short noise bursts. Beacons whose idents begin or end with an 'E' can be mislogged easily. For example, when the weak Belize NDO OZE-392 is up to its neck in general LF band crud, It can sound like BZ for many repetitions in succession. It might be mistaken by a beginner for OZ-393 Oklahoma, although careful attention to the freuency domain parameters and cycle timing should act as insurance against that. Formats In broadcast (BCB/SWBC/FM) DXing, It is standard practice for the DXer to specify the program format of each station heard, whether in reporting to DX newsletters, requesting QSLS.' or compiling station directories. In NDB DXing, we should do the same, except that we naturally won't be referring to rock, NOR, classical, etc. With NDBS. the format consists of what happens between the Morse idents. To the beginning DXer in the central US or Australia, it must seem that all NDBs simply transmit their ident over and over continuously. After some experience, however. it becomes clear that there are many other formats In use around the world. One of the main goals of the Checklists (now part of the NDB DX Newsletter) has been to come up with a systematic approach to these variations in format. As with the frequency domain fficial government sources are next to useless; their databases are woefully incomplete, obsolete, and Inaccurate. So. with the proviso that DXers are not perfect In global coverage or available time, this chapter presents two tables summarizing our results to date. More Input is very much needed, particularly from DXers with information on parameters of NDBs In Europe and Africa. Table I describes all known formats currently in use. along with their abbreviations as adopted in the Newsletter. Two special formats require detailed description. One is used by VND-320 in the Torres Strait between Queensland and Papua New Guinea, with the ambitious objective of conveying tide-height data to mariners. In slow Morse, it first transmits 3 minutes of VND Identification in the DA21D format. Next it sends the tidal height for Booby Island. 'TIDE TIDE T' and a ' series of dots which tell the height. Then another 3 minutes of Identification followed by the tidal info for Turtle Head. 'TIDE TURTLE ND T' and the series of dots. Further information (from Australian readers) on this unique beacon, and the deciphering of the dot format, would be appreciated. The other special format is known as CONSOL, and is a special directional signal transmitted to mariners who can use it to navigate crudely without any need for the usual direction-finding receiver. The CONSOL station uses three wide-spaced vertical antennas, specially phased to produce a rotating beam pattern. In the receiver, a series of dots is heard at the rate of 2 per second, which gradually blend into a continuous tone, and then into a series of dashes. The listener counts the number of dots and the number of dashes, then refers to a conversion chart or map to determine his approximate bearing from the transmitter. If this procedure is then followed with another CONSOL station, a rough positional fix is achieved. The directional signal takes 30 seconds to transmit. and is followed by 5 seconds of silence, one or two idents. and a 10-second dash. The whole cycle thus takes 60 seconds before repeating, so is considered too slow for use by aircraft, though of course the usual ADF bearing can be taken as with any other beacon. While the CONSOL format has been discontinued in the western hemisphere and much of Europe, it is still very much alive in the USSR and Japan. Indeed, the powerful CONSOL outlets on 340 and 372 kHz from the Soviet Far East are widely heard in the western US. If anyone can provide the conversion chart for these two outlets, it would be of great interest. Table 2 shows which formats are used in various countries, again based solely on reception by DXers. In this table, the LP and VLP formats are Included in the plain category. Note that many entries are labeled 'occasionally.' This is due to the common use of dual transmitters for insurance against outages; sometimes the two transmitters will have differing formats. Normally this is not the case for US, Canada, New Zealand. or Australia. In past years. some FAA-maintained NDBs used an extra-long gap between the second and third letters to indicate the backup transmitter (see Larry King's article in the June 1974 Lowdown). but evidently this practice is no longer followed. From this writer's visits to western US NDBs, it appears that most of them have only one transmitter. In Canada, per Harold Sellers' item in the May 1987 Lowdown, the DAID is supposed to be slightly truncated without reducing the overall cycle-length, but I have seen no reports of this scheme actually being observed. To the contrary, DXers' measurements show that some Canadian NDBs have greatly different overall cycle lengths between their two transmitters. This matter of cycle length and precision timing will be the topic of the next chapter, along with a discussion of NDB schedules.
Thus ends "On The Art of NDB DXing" as it now stands. The series was not finished, but could eventually be finished if there is sufficient demand.
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