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Build this shortwave e a Try this antenna switching arrangement and improve your shortwave reception. By ED NOLL If you've ever had difficulty in capturing those frequencies on the fringe of the shortwave spectrum, you probably know what a blessing it would be to have more than one antenna at your disposal. Now you can - well not really, but the Flexo SWL Aerial can make it seem as if you do. The Flexo SWL Aerial is an antenna/antennaswitching system that improves reception by adding flexibility to a single antenna installation, making it seem as if you have more than one antenna. Flexo's extended performance better accommodates the extraordinary frequency span occupied by the many shortwave broadcast bands. In effect, you have more than one choice in dealing with the variables of antenna length, line length, angle-of-signal arrival, and propagation conditions. With the Flexo, sensitivity is made more uniform over the entire shortwave spectrum. It provides more than one choice in finding an optimum signal-to-noise (S/N) or signal-to-interference ratio when attempting to pull in a specific station. If you listen only to strong signals, the Flexo won't do much for your receiver's performance because of the high-sensitivity, high -- --8) PLUG 1 TO - - - LY RECEIVER (a) Slb Flg. 1 selectivity, and automatic-gain characteristics of the latest receivers. However, if difficult receiving conditions and weak-signal identification are your bag, give it a try. When a signal is weak, despite the high sensitivity of the receiver, even a couple of dB of extra input signal may help you obtain an ID. Even the strong signals are subject to brief fades, so a more solid lock is attractive to the music-loving enthusiast. Since the needs of shortwave listeners tend to vary, we'll describe both a simple two-wire Flexo and a really different three-wire version. The two-wire Flexo A complete Flexo antenna and switching arrangement is given in Fig, 1. Basically, as shown in Fig. la, the antenna is cut as a dipole on the 60-metre band. A coaxial transmission line feeds the signal to the Flexo switch and another short piece of coax (not shown) then feeds the switch output to the receiver. Note that one antenna wire is angled by 45 degrees in the horizontal plane from the more usual straight line position. (b) Fig.1 - the two-wire Flexo SWL Aerial gives you four possible combinations. When S1 selects position 1, the left-hand element is connected directly to the centre conductor, which feeds the signal to the receiver. Position 2 connects the element that's offset at a 45-degree angle. In position 3, both elements connect to the centre conductor. Position 4 gives a dipole configuration with one element connected to the centre conductor and the other connected to the braided shield. JANUARY 1988 71 14.33m PARTS LIST FOR THE FLEXO SWL AERIAL J 1 - Insulated phono jack S1 - 2-pole, 4 or 6-position switch (see text) Antenna elements - bare copper wire, AWG #16 or #14 Antenna mast - PVC pipe (see text) Down lead - coax cable or insulated wire (see text) Metal box, guys, nuts, bolts, etc, 120 ' 120' ..~'J,'!,I'> As shown in Fig.1 b, the two antenna elements can be angled also by as much as 30 degrees in the horizontal plane from their usual positions. Thus, they can be positioned to accommodate the mounting space in your back yard. In tests, it has been found that more reception flexibility is obtained with one element angled rather than straight. The antenna performs pretty much as a dipole on the 41 to 60-metre bands. On the remaining higher-frequency bands, other switch settings were often preferable to the dipole connection. Remember that the antenna wires become longer in terms of wavelength at the higher frequencies and, therefore, often perform more like a long wire. The antenna mast was made of telescoped sections of PVC piping (as shown in the photos). The coaxial transmission line is fed to the top of the PVC mast by cutting a hole in the mast at about chest-height. Fig.1 shows how the inner conductor and conducting braid (outer conductor) of the coaxial line are conneoted at the top of the mast. Two bolts serve as the antenna terminals. It is to those terminals that the antenna wires were attached using solder rings. The elements were then stretched out in an inverted-V fashion and brought down to two metal fence posts at ground level. In effect, you are constructing a 60-metre inverted THREE WIRES, -:::::: LOOSELY LOOPED - PLUG 1 S1a - - - - - ~ E R ----CJ' S1b 30 20 Fig. 2 Fig.2 - The three-element Flexo installation provides greater flexibility over the two wire type by allowing six combinations. dipole, but one with the antenna wires not necessarily in line. There are four possible ways to use the two conductors at the receiver end of the coaxial transmission line. You can use the two separate conductors individually (an either-or arrangement), or connected in parallel. The fourth arrangement is to The coax cable is fed through a hole, drilled about chest-high in the PVC piping, to the top of the mast. This view of the top of the PVC piping shows that the coax cable terminates in large crimp-on lugs, which are then secured to the mast using nuts and bolts. The antenna wires are then connected to the bolts. 72 SILICON CHIP use them in dipole fashion. The four possible choices are made available by a four-position, two-pole switch. The two switch sections are shown as Sla and Slb in Fig.la . In switch position 1, the braid of the coaxial line from the antenna is connected to the inner conductor of the short section of coax line that runs to the receiver input. In effect, the coaxial braid and one of the 14.3-metre antenna wires are being used as a single~ wire feed antenna. Notice that the braid does not connect to the centre conductor of the coax line. On position 2 of the switch, the centre conductor of the coax line and its associated antenna element serve as a single-wire antenna. In position 3, the braid and the centre conductor of the coaxial feed line coming from the antenna are connected to the inner conductor of the short section coax line that channels the input signal to the receiver. Thus, both antenna wires are connected to the receiver in a single-wire feed arrangement. On position 4, the centre conductor and braid of the antenna coax are respectively connected to the centre conductor and braid of the receiver coax. Thus, when position 4 is selected, the antenna operates as a true dipole. In putting the Flexo switching arrangement together, you must make certain that the braid of the transmission line from the antenna is not connected directly to ground in the switching box. The only time that the braid is connected to ground is when S1 is in position 4. In the author·s switching arrangement, the switch was built into a small metal box measuring 80 x 55 x 100mm. On the rear of the box, the author mounted two isolated terminals (as shown in the photos) to which the coaxial line from the antenna is PVC MAST CONSTRUCTION An antenna mast can be easily built from telescoping setions of PVC tubing and a few nuts and screws to hold the structure together. A 1 .5-metre metal fence ROSt, embedded in the ground, is used as a foundation for the mast. Two 3-metre sections of PVC tubing can be used to cqnstruct a mast about 5 .4 -metres high. Begin with a 5cm diameter section of PVC tubing and insert a second 3 .8cm diameter section of tubing, to a depth of 60cm, into one end . Drill holes through the overlapping sections of tubing and bolt them together. Insert and connect the signal carrying cables as needed. Connect the wires that will Ii JI THROUGHBOLTS '---..... GROUNO LEVEL - - - ~ - - 11 11 11 II jJ In the three-element installation, the down leads are run down the outside of the PVC piping through screw-eyes, and are connected to the feed-in by bolts installed through the mast. act as the RF (radio frequency) pick-up elements . If guys are to be used, cc;onnect them now . Use nylon stranded rope - the smallest diameter you can buy. Drop the mast 0ver the fence post and secure with bolts. Finally, secure the guys. Taller masts can be built by using ionger or additional lengths of PVC tubing. If a taller mast is desired , simply add to the length by joining two 5em diameter sections of PVC tubing , using a 1-metre length of 3.8cm tubing as a joint support. Insert the joint support about 60cm into the lower section of the mast. Drill holes and bolt the two sections together. Secure the upper section in the same manner, with the two outer lengths of tubing forming as tight a joint as possible . Finish up by adding the RF pick-up elements , signalcarrying cables , etc. as needed. JA NUA RY 1988 73 connected. To the left of these is a shielded phono jack to which the coaxial line feeding the receiver is connected. If you have trouble finding a two-pole, four position rotary switch, a two-pole, six-position switch may be substituted. The three-wire Flexo Another Flexo aerial uses three antenna wires and a three-conductor transmission line as shown in Fig.2. In that arrangement, the three antenna wires are spaced 120 degrees in the horizontal plane. It, too, is erected in the inverted-V fashion. The ends are dropped down to three metal fence posts near ground level. A view of that configuration is shown in one of the photos. The three transmission line wires run down the outside of the PVC mast through screw eyes to three terminals that are mounted in the PVC piping at chest level. From there, a three-wire transmission line enters the radio room and connects to the Flexo switcher. When there are three wires that are part of the transmission line, there are as many as twelve individual combinations that can be switched in. However, the six combinations provided by the arrangement shown in Fig.2 give good results, and little improvement can be obtained with additional combinations. The switching arrangement shown can select any individual wire for use as a long-wire antenna. The remaining three positions use the antenna wires in three separate dipole configurations. As a result, the Flexo has some limited directivity when operating as a switched dipole configuration on the lower-frequency bands. On the higher-frequency bands, the single-wire combinations also display directivity. However, the main advantage is that it gives you six combinations to choose from in obtaining the best reception possible for difficult propagation and interference conditions. Don't expect it to be a cure-all; some additional ·• The switch box is simply an inexpensive metal cabinet that carries the selector switch, two screw terminals and a phono jack. options may be necessary under difficult conditions. The switch is a two-pole, six-position type as recommended previously. Note that Sla selects one of the individual antenna wires when in positions 1, 2 and 3. Those same positions on Slb are left unconnected. Thus, you are operating with a singlewire feed for the first three positions and true coaxial feed for the latter three positions. The last three positions (4, 5 and 6) of switch Slb connect the wires in pairs to give a dipole configuration. In the 4, 5 and 6 positions, an appropriate antenna wire is connected to the braid of the small section of coaxial line that connects the output of the switcher to the receiver. In checking out your results, it may be advantageous to wire the switcher in terms of the physical positioning of each antenna wire. In wiring the Flexo switch, be certain to mount three insulated terminals on the box for connecting the wires from the antenna. You can use the same size box as for the previous antenna. ~ Evolution of Electric Railways: ctd from p.7 of the train line pipe, commonly known as "pulling the train's tail". By 1950 the railway world was changing fast. Diesel electric locomotives had been increasing in numbers since the war years and superseding many steam locos. The first advantages claimed for the diesels were quicker starting and longer times between overhauls. As for running cost measured in dollars per ton-mile of train hauled, on some American railroads the diesel electric could do no better than existing steam locomotives. In many countries , including Australia, running costs of old worn-out steam plant serviced in ancient loco sheds did exceed the expense of servicing and refuelling 74 SILICON CHIP new diesel electric machines in brand-spanking new service shops. A few United States railroads did show clearly that a large ·modern steam locomotive could be serviced and refuelled in a well-equipped running shop at a cost less than or equal to the equivalent expense for diesel electric units of the same power. The Norfolk & Western Railway was one such line which built its last steamer in 1953 and continued to use steam locomotives economically right up to April 4th, 1960. Even then, economy was not the reason for the death of steam. The problem was that they were just about the only railroad left using steam and new parts and plant became virtually unobtainable. It is interesting that the major manufacturers Alco, Baldwin and Lima in America built their last steam locomotive in 1947, 1949 and 1949 respectively, while in Australia the last steam locomotive to enter service, in January 1957, was a 269 tonne giant, the articulated Garratt built by Beyer, Peacock & Co Ltd, of Manchester England. So ended the amazing 160 year steam era, with the diesel-electric locomotive now ruling the world's lines. But let us not forget the other contender, the electric locomotive which is widely used around the world, expecially in Europe. Next month when we will delve into Australia ' s part in this fascinating saga. ~