On The Art of NDB DXing
by Sheldon Remington
©
1987-2000 All Rights Reserved
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CHAPTER TEN: BEACONS ON THE ROAD
April has arrived, and our thoughts begin turning to planning a summer vacation. Maybe we'll go touring in a car or on a bike, maybe we'll jet to a resort area, maybe we'll even take to the water on a cruise. We'll visit with relatives and friends including fellow DXers, or we'll immerse ourselves in nature; sooner or later we'll find ourselves in almost any conceivable location. We'll say goodbye to the radio gear for a while--hey, wait a minute! We are radio enthusiasts, and we know what a spectrum of enjoyment can be gotten from a receiver. So why should we cut ourselves off from a whole additional spectrum of fun just because we're not at the home QTH? For us longwave specialists, there are several interesting activities we can partake of when touring, the two main ones being DXing, of course, and visiting beacon transmitter sites, both NDB and Lowfer. Of special value to the DX community at large is the making of band-scans at locations normally lacking in resident DXers. Every location produces its own set of dominant signals, and many of these will be hotly sought after by more distant listeners, so we can supply important clues that will benefit everyone. Thus every trip, even business trips, can act to multiply our effective geographical coverage. And we can join forces with another DXer for a shared DXpedition, for even more fun and productivity. Portable Receivers The first thing we're going to need is some sort of battery-operated receiving equipment, but there are plenty of ways to achieve this. Even if our LW receiver can be powered only from AC, as with most surplus units, it could alternatively be supplied by a small 12 VDC to 117 VAC inverter (for about $60 and up), which in turn is powered by the vehicle supply or other large 12 V battery. However, these receivers are usually heavy and bulky, so the whole assembly can become unwieldy unless we're really dedicated. More practical is to use a modern solid-state receiver (or transceiver), nearly all of which can be powered directly from a 12 V supply. Such rigs as the R71A, R5000, TS430, TS440, TS450, FT757, FT990, IC765, to name a few, make superb portable/mobile receivers, and are ruggedly built to withstand the rigors of field operation. They typically have a current drain on the order of an amp, so we'll need something more substantial than D-cells for extended listening. But any healthy vehicle battery can supply that current several nights or days with little risk of depletion, even without the engine recharging it. We can also use a separate battery, preferably a rechargeable one. Best of all are the deep-cycle lead acid types used for photovoltaic, marine, and golf cart systems. Plenty of details on the care and use of large batteries can be found in ARRL literature. A good reference to start from is a two-part series by our own Michael Mideke in Sept. and Oct. 1987 QST, entitled "Alternative Energy-An Overview of Options and Requirements." Incidentally, if we do use an independent battery in a car, it's still a good idea to ground the receiver to the car body, especially with digital rigs. Another approach, which is a lot less expensive if we're starting from scratch, is to acquire a true portable, i.e., a radio with self-contained batteries. Of course, none of these will be very satisfying for long-term, serious beacon DXing. But they have many other uses; for instance, if we operate or plan to build a 1750-meter beacon, we can use the portable for all kinds of tuneup and range testing. And if you've never listened to NDB's and Lowfers on a radio while you hold it in your hand, you're missing a real thrill. For some time now, Sony Corp. has been leading a wave of innovation in small, digitally-synthesized portables. First with the ICF-2001, and later with the 2002 (= 7600D outside the U.S.) and the 2010 (= 2001D outside the U.S.), Sony has offered many of the attributes of a communications receiver in a moderately-priced package about the size of an average book. Best of all, all three of these receivers cover the LW beacon band. The 2002 can be obtained for under $200 (check the ads in the photography magazines), and the 2010, for somewhat more. And according to Radio Netherland's Medianetwork program, Sony is due to introduce their SW-1 this summer (1988). While it lacks the BFO and fine-tuning capability of the 2002/2010, it does have seamless 150 kHz to 30 MHz coverage, plus FM stereo in headphones, keypad frequency entry, memories, and a price in the same class as the 2002. The shocker: it's the same size as a pack of cigarettes! Some other manufacturers, such as Panasonic and Radio Shack, are doing their best to keep up with Sony, so one may find comparable products from them, although usually a couple of years later. On an even more economical basis, there are a few analog portables with longwave coverage. Or we could modify a portable to add LW, either by adding inductance to the AM (MW) band, or by using a converter (sources in Chapter Two). The same applies to car radios as well. Finally, those who really enjoy RF design and construction could build an excellent custom portable receiver from scratch, as Mike Mideke has done. Mobile and Temporary Receiving Antennas While the self-contained portables provide a whip and/or a loopstick for reception, these will be pretty useless inside a car or other metal structure, and even in the clear they can't provide the signal strengths of a larger external antenna. Of course, the real communications receivers have no internal antenna at all. For use while mobile-in-motion, there is only one practical solution: the active whip. These have already been discussed in Chapter Two, but now we must find a way to attach them to the vehicle, preferably on the rooftop, that will be secure with high wind forces. The easiest way is to clamp them to a permanent or temporary roof luggage rack. In fact, a roof rack can hold several whip antennas for various parts of the radio spectrum, if the DXpedition is an ambitious one and we don't mind quizzical looks from passerby. Another method is to use a commercial CB whip which then supplies the mounting base, whether magnetic, clamp-on, or permanent. The bottom of the whip can simply be connected to the input of the preamp, which is mounted on the antenna base, with a normal coaxial downlead. If necessary, whips can even be guyed with heavy monofilament secured to the front of the vehicle, sometimes with musical aeolian wind sounds. To preserve full sensitivity with the ignition running, we may need to suppress interference sources in the vehicle electrical system; Nelson's Interference Handbook and ARRL books discuss the methods. Then we can cruise along, making lots of interesting observations. We can park the receiver on a marginal beacon signal, listening to the great effects of terrain and man-made structures on the signal strength. We will also be nicely equipped to track down noise sources, PLC's (Powerline Carriers), etc., and for checking the coverage of our 1750-meter beacons. But now it's April, and we're probably thinking of our vacation not so much in terms of being in motion but rather as being one or more destinations. Since active bandscanning is difficult while driving, this is where the real DXing can come play. But even so, a good mobile setup will be invaluable for checking out DX locations for powerline noise levels, before stopping to set up camp. The other important considerations in site selection are low horizons, minimum distractions from traffic or other activity, and, if possible, proximity to ocean or lake shorelines. At a fixed location, even if only temporary, we can draw upon our arsenal of more substantial antennas. Chief among these are the horizontal end-fed wires. These give good signal-to-noise levels (dynamic range is practically infinite) that we can take full advantage of our chosen noise-free vacation spot. A lot of the fun of DXpeditions is trying out different lengths and orientations or wires, perhaps several at once, with a selector switch. Local terrain is a major factor in the directivity of such antennas; for example, a pair of wires run at right angles, with some small hill or ridge separating them, will be surprisingly good at isolating DX signals from different directions. Since these low horizontal wires are so non-critical in their installation, it is easy to lay one out at a listening site upon arrival, and just roll it up the next day before departing. In fact, experience has shown that taut, post-mounted beverage wires invariably become terminated by stray cows or deer during the night. So the best procedure is just to take a sunset stroll along the beach or through the woods, carrying a stick or rod which holds a freely-turning spool of single-conductor insulated wire. When we begin the walk, we fasten the end of the wire to an anchor near the receiver, so that as we proceed, the wire will be pulled off the reel. The wire can be draped over convenient low branches, or even on the ground. It may even turn out to be a more adventurous walk than it would be without the wire, since we should travel in a fairly straight line, regardless of obstacles. If we don't anchor the far end of the wire, and bring the empty reel back to camp, rolling up the antenna later can be done without another walk. In order to avoid sore wrists when winding up the wire, get a polyethylene hose reel on a low stand, with a hand crank (try Sears). These can hold miles of wire, and have such a large hub that a long Beverage can be rewound in five minutes. It could be kept in the car trunk, and can remain there as we walk away pulling the end of the wire with us. LWCA and IRCA member Don Moman has succeeded in actually motorizing his Beverage spool, and we'd all appreciate a diagram and description of this invention. Recommended wire lengths range from perhaps 100 feet to over 2000 feet. Shorter wires may not give good signal strengths, while wires that are too long may have such a narrow main lobe that it only produces DX signals from a small region. Experimentation will teach us the optimum compromise length for each DXpedition situation. Recent results indicate 500-800 feet is optimum for the high-frequency end of the NDB band, and 1200-2000 feet works best for the low-frequency end. A good bargain in wire, at about 2.8 cents per foot, is the five-conductor flat antenna rotator control wire, available in 100-foot hanks from Radio Shack #15-1201. This is AWG 20 gauge stranded copper, with very rugged brown (for camouflage) insulation. The five wires can be zipped, spliced (solder and heat-shrink tubing, please), and wound onto a reel. Hamfests can also be good sources of Beverage wire. Another, even quicker way to get a long, low, horizontal wire is to find one already installed: a wire fence. This technique may have originated with BCB DXer Glenn Hauser; it consists of simply using a short connector wire from the receiver to an alligator clip, which attaches to a fence wire. The posts, of course, must be wooden, and it's a good idea to watch out for insulators, which imply an electrified fence, a hazard to the receiver front-end and often a source of electrical noise. Presto, an instant Beverage, if the fence is long and straight. Maybe we can luck up on a corner where two fences diverge at right angles, and switch between them. Loops and Direction-Finding The other special antenna we can pull out at our listening sites is the loop. As discussed in Chapter Four, loops can be ferrite or air core, tuned or broadband, and small or large, in which case the Kauai Collapsible Loop will be just the ticket. Tilting is not so important if we have found a noise-free location; in fact, bearings should always be taken with no tilt, even when the null is deeper with a tilt. Loops are especially useful when we're on tour, since we can get directional bearings on unidentified signals from angles not normally occupied by DXers, giving a wider baseline for triangulation. Unfortunately, DF'ing has been neglected by the LF DX community, though many have loops capable of fairly precise nulling. It is important for triangulation to specify bearings within +/- 5 degrees of azimuth, while a carefully-balanced loop can achieve precision of +/- 1/2 degree or better. Obviously, use of such terms as "east/west" for bearings will do little good, if the actual bearing is 84 degrees/264 degrees. We need to have a compass rose and pointer, affixed to the base of the loop, calibrated not in cardinal points but in degrees of azimuth. The compass rose can be a circular protractor, available in various sizes at stationary stores, or more deluxe ones can be found in nautical supply stores, or we can make our own. Most loops have a pattern asymmetry, so it's best to average two bearings if they're not 180 degrees apart. Also, skywave propagation produces slow variations in null bearings, so it's a good idea to take the average of several readings taken at different times. Some practice will go a long way; try taking a series of bearings on a known NDB a few hundred miles away, and compare them with a mathematical bearing based on the NDB's coordinates. An in-depth treatise by Gorden Nelson on DF'ing DX with loops is available as a reprint from the NRC. It is not essential to precisely locate true north for geodetic alignment of a loop. A bearing specified as "12 degrees +/-5 degrees clockwise from beacon XYZ" can be normalized later by calculation, and may even be the best way if XYZ is in the same general region as the target. If our tour has multiple stops, a series of bearings taken at each stop and then plotted on a good map with a protractor and straightedge, will yield a definitive triangulation of that signal's location, and it can be all done by a single intrepid DXer. Of course, the traveler himself can then home in by taking further bearings as he gets closer, and visit the transmitter in person. One such search was conducted in March of 1986 by Steve McGreevy and
myself. An unidentified NDB signal had been sending TST on 212 kHz for a
few months, and we knew it couldn't be too distant since it was audible
day and night. We started north with no clues whatsoever except our loop
bearings, but after a very enjoyable afternoon of homing, we found
ourselves over 100 miles away in Oroville, California. It turned out to be
a brand-new aero NDB being tested by the FAA, slated to use the indent
"OVE." So everyone was able to count it in their logs, despite the fact
that it went off the air the next day! Numerous other long-lived unID
beacons are reported by DXers, but most of them will remain mysteries
until we start taking precise bearings, at home and on Dxpeditions.
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