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What’s your DAB+ reception like? Spasmodic? Subject to spitting and dropouts? You need a decent antenna rather than rely on the nearly useless extendable whip antenna fitted to most DAB+ radios. This 5-element Yagi antenna is specifically designed for DAB+ radio and should markedly improve your reception. In some cases it could mean actually receiving DAB+ signals where there are now none! Build this 5-Element Yagi Specifically For By LEO SIMPSON M any people these days have DAB+ radios but they are often disappointed in the reception, even though they may live quite close to the transmitters in Australia’s capital cities. They buy a DAB+ radio because they have been sold on the “clean, clear digital sound” that it is supposed to have. But often, the results are less than expected, mainly for two reasons. 36  Silicon Chip First, virtually all DAB+ radios come with an extendable whip antenna which does double duty for FM and DAB+ reception. Truth is, these whip antennas are at best a compromise for either mode. Nor do most DAB+ radios have an antenna socket into which you can plug an external antenna. So the average listener is stymied – even if they want to improve reception. And the second reason why DAB+ sound quality is generally disappointing is the that digital data rate (ie, at the station) is simply too low for good quality sound. This means that a station broadcasting on FM and DAB+ will typically sound much better on good old “steam-driven” FM stereo multiplex transmissions. (And before any of our readers email siliconchip.com.au us about the “steam-driven” comment, think about it. FM transmitters are “steam-driven”; or at least, most of them are in Australia!) Even so, a DAB+ radio fed with a good signal will always have a quiet background, no “spitting” and will sound quite clean to most ears. So this article will describe how to build a good DAB+ antenna and also, tell you how to fit an antenna socket to your radio so you can feed the improved signal into it. By the way, if you go on-line to see if you can buy a DAB+ antenna, you can’t. As far as we can tell, they are simply not available. The closest you will come is a DAB antenna from the UK. Don’t buy one of these as they are not cut to suit the DAB+ transmissions in Australia. UK DAB uses the band from 215 to 230MHz. Vertical polarisation All of the DAB+ transmissions in Australia are vertically polarised. That means that any receiving antenna must also be vertically polarised. That brings about an important constraint about how the antenna is mounted on a metal mast, as we shall see shortly. As with the FM antenna presented in last month’s issue, this is a 5-element Yagi design but is half the size of the FM antenna because it operates at roughly twice the frequency. All of the DAB+ transmissions in Australia’s capital cities (Adelaide, Brisbane, Melbourne, Perth and Sydney) are in three bands: 202.928MHz (9A); 204.64MHz (9B) and 206.928MHz (9C). Canberra and Darwin have experimental transmissions centred on 211.648MHz (10B). The Yagi antenna presented in this article is designed to cover all the DAB+ bands in Australia. It has a measured gain of about +12dB with respect to a whip antenna. However, that figure is with respect to a dipole which has a ground plane. Unfortunately, the whip antennas in DAB+ radios do not have adequate ground planes so their performance is even worse. With good “line of sight” reception, a 5-element Yagi antenna like this should give reception at quite long distances from the transmitter, perhaps 100km or more. However, we have not tested this aspect. We can vouch for the gain figure though (as detailed later in this article). Tools you will need Most enthusiasts will have all the tools needed for this project. You will need a hacksaw, electric drill and a vice. It would also help if you have a drill press but you can do without this. Apart from an antenna clamp (Ubolt and V-block), no special hardware or fittings are required. Tube cutter Last month we noted that a tube cutter is a very handy tool in an antenna project such as this. You end up with smooth square cuts with no swarf. We The “Digital Cliff” Unlike analog broadcast radio (AM or FM) but very similar to digital TV, with DAB+ radio you have either got a signal, or you haven’t. There’s virtually no middle ground! It’s the dreaded Digital Cliff – the metaphor is that if you don’t have enough signal (or, perhaps surprisingly, too much signal causing overload) digital radio or TV falls off the cliff and you get nothing. Of course, either digital radio or TV might be trying to tell you it’s struggling, with continual dropouts and break-up when it’s just on the point of teetering over the edge – most listeners or viewers would not tolerate this and turn off. It’s often found that weather can also push reception over the cliff. The big advantage of this project is that the gain of the Yagi can lift your signal to the point where you get reliable levels; enough to give you good reception. The other side of this is that DAB+ is currently transmitted only in the mainland capital cities – even those in closeby urban centres (Central Coast/Illawarra/Blue Mountains around Sydney and Geelong/Mornington Peninsular around Melbourne, for example) find DAB+ signal levels are just too low for reliable reception. With 12dB of gain, we would expect this antenna will bring a lot more listeners into the DAB+ family! Compare this DAB+ Antenna with the FM Antenna published last month: it’s about half the size. Funny, that! siliconchip.com.au November 2015  37 The ends of the folded dipole are fabricated using 42mm lengths of aluminium tubing shaped to mate with the upper and lower pieces. They are held together with 50mm long machine screws, nuts and split washers. The dipole insulator plate has wing nut terminals to connect 300Ω ribbon or a 300Ω-to-75Ω balun. The plate is made from Per­spex, Lexan or other acrylic material. The square boom makes mounting easy. This “Waterfall” screen grab shows the signal picked up by the 5-element antenna from a location in Sydney’s Arncliffe, aimed at the Redfern DAB+ transmitter (<5km away). It shows the signal levels of the three bands (9A, 9B & 9C). This measurement was taken by the Signal Hound USB Spectrum Analyser (from Silvertone Electronics [www.silvertone.com.au]). used a Bunnings product, the Haron Model STC330N. When using this cutter, it is important not to rush the job. Mark the position of the cut on the tube with an HB pencil and then position the blade of the cutter precisely on the mark, with the tube sitting between the rollers. Apply very light pressure with the knob of the cutter and then measure from the end of the tube to the blade of the cutter, to make sure you are cutting to the exact length you want (to be sure, to be sure!) Actually, if you have not used one of these cutters before, do a couple of practice cuts on scrap plastic conduit, just to get the feel of the whole procedure. You are also likely to find that because the tube is very smooth and quite small in diameter, it is hard to get a grip on it as the cut deepens. Gripping the tube with a rubber kitchen glove makes it a lot easier. Buying the alumimium By comparison, this Spectrum Analyser display was taken with a vertical whip antenna adjusted to 368mm long (1/4 wavelength) and with a substantial ground plane. As you can see, the received signal level is about 12dB less than that received with the 5-element Yagi described here. 38  Silicon Chip For convenience we purchased the 10mm round aluminium tubing and 19mm square aluminium tube from the local Bunnings warehouse. They stock the 19mm square tube in 3-metre lengths and the 10mm tubing in 1-metre lengths. So we purchased six 1-metre lengths of the 10mm tube and one 3-metre length of the 19mm tube. Total cost: $33.98. You might be able to purchase your aluminium from a nearby metal supplier and in that case, they might also cut it to the various lengths you will need (perhaps for a small extra charge?). One drawback of buying tube from Bunnings is that every item you pursiliconchip.com.au ements, many antennas are in a poor state. Aluminium may not “rust” but it does oxidise, particularly in seaside areas or in metropolitan areas where there is a lot of industrial fallout. Corrosion will also be a lot worse if you don’t use the right screws and nuts. We strongly recommend the use of stainless steel screws, nuts and washers throughout, whether for ma- chase has an adhesive label attached which is obviously meant to last for longer than the life of the product! At least, it seems that way when you are trying to remove seven labels – it took ages! At least I ended with highly polished tubes! Screws & nuts After a few years’ exposure to the elREFLECTOR 750mm LONG FOLDED DIPOLE 692mm LONG SECOND DIRECTOR 664mm LONG FIRST DIRECTOR 670mm LONG chine screws or self-tappers. They do cost a little more but they last indefinitely. You will find a good array of stainless steel screws available from ships’ chandlers. Don’t, on any account, use brass screws. When used to attach aluminium elements these will corrode away almost before your eyes. Nor do we recom­mend galvanised, bright zinc or THIRD DIRECTOR 670mm LONG CL B 26 HOLES FOR V-BLOCK CLAMP (TO MAST) 26 BOOM: 1250mm LONG 120 A A A F A CL 26 26 B 50 300 125 CL ALL ELEMENTS CUT FROM 10mm OD ALUMINIUM TUBING 340 340 6 D 300 300 200 692 288 6 26 332 FOLDED DIPOLE INSULATOR (MATERIAL: 3mm THICK ACRYLIC) (HOLES 4mm IN DIAMETER) 28 288 26 12 332 6 DIPOLE UPPER ELEMENT (1 REQUIRED) (HOLES 4mm IN DIAMETER) 6 DIPOLE LOWER ELEMENTS (2 REQUIRED) (HOLES 4mm IN DIAMETER) 13mm LONG 8G STAINLESS STEEL SELF-TAPPING SCREW ELEMENT 19 27 E BOOM DIPOLE END SPACERS (2 REQUIRED) MATERIAL: 10mm OD ALUMINIUM TUBING M4 x 50mm SCREW F DIPOLE CENTRE SPACER (19mm LENGTH OF 19mm OD PVC CONDUIT) A DETAIL OF DIRECTOR & REFLECTOR MOUNTING TO BOOM M4 x 50mm SCREW BOOM UPPER ELEMENT UPPER ELEMENT M4 x 32mm SCREW M4 x 19mm SCREW E LOWER ELEMENT M4 NUT & LOCKWASHER B FOLDED DIPOLE END DETAIL (ALL DIMENSIONS IN MILLIMETRES) M4 x 32mm SCREW F M4 x 19mm SCREW D M4 NUT & LOCKWASHER LOWER ELEMENT M4 NUT & LOCKWASHER M4 NUT & LOCKWASHER FLAT WASHER FLAT WASHER M4 WINGNUT M4 WINGNUT CENTRE OF DIPOLE ASSEMBLY DETAIL Fig.1: this diagram shows all the details of the 5-element antenna. At top is a plan view while the other diagrams show hardware and element mounting details. siliconchip.com.au November 2015  39 This topside view of the antenna shows how the folded dipole is attached to the square boom. Note the short section of PVC conduit which acts as a spacer between the underside of the boom and the dipole insulator plate. Whitworth or other machine screws hold it all together. cadmium-plated steel screws. In seaside areas these can be visibly corroded with just a few days’ exposure. In rural areas, away from the sea or city pollution, you can probably get away with galvanised screws but the antenna will last longer if you paint it. Starting work Constructing this antenna is quite straightforward. If you have all the materials available you can probably The reflector and director elements are attached to the boom using self-tapping screws. Ideally, all screws, nuts and washers should be stainless steel to avoid corrosion. To check that screws are stainless, take a magnet with you when buying them. If they attract, they ain’t stainless! do it in a couple of afternoons. Fig.1 shows all the details of the 5-element antenna. It shows the dimensions of all the elements and the various hardware bits you will have to make to assemble the antenna. At top is a plan view showing the length of all five elements and their spacing along the boom. Before you start, make sure you have obtained all the alu­minium and hardware listed in the Parts List. You will be frustrated if you get half-way through and find you can’t progress further because you lack screws or some other item. Get ’em all before you start. You need to cut the 19mm square tube (the boom) to length and then mark it for drilling and this is where it is quite easy to make mistakes. If you are experienced in metalwork and have access to a set of vee-blocks and a drill press, you could substitute 25mm diameter tubing for the boom. In fact, you could use 25mm stain­less steel round tubing which is readily Current DAB+ Transmission Sites around Australia (as at 5 October 2015) City Transmitter Location Adelaide TXA Crafers Site Tower 115 Mount Lofty Summit Road CRAFERS Brisbane Brisbane TXA T-Site Tower 445 Sir Samuel Griffith Drive MOUNT COOT-THA Broadcast/Comms Tower Digital Distribution Australia Site Mount Mee Rd MOUNT MEE Melbourne Melbourne Melbourne Melbourne Melbourne TXA Ornata Road Site Tower 12 Ornata Road MOUNT DANDENONG Broadcast/Comms Monopole Pioneer Concrete Site 213 Boundary St PORT MELBOURNE Broadcast/Comms Tower Roof 101 Collins Street MELBOURNE Crown Castle Site Bald Hill off Swans Rd DARLEY Tower Broadcast Australia Site Eyre Road MOUNT DANDENONG Perth Perth Perth Crown Castle Site Cnr Mulgrave Loop and Bergen Way MINDARIE Central Park 152 to 158 St Georges Terrace PERTH TXA Carmel Site 255 Welshpool Road East CARMEL Sydney Sydney Sydney Sydney Sydney Sydney Sydney Sydney TXA Artarmon Site Tower 192-196 Hampden Road ARTARMON TXA Willoughby Site Tower 15 Richmond Avenue WILLOUGHBY Broadcast/Comms Tower Sydney Tower Westfield Centrepoint 100 Market Street SYDNEY Broadcast/Comms Monopole Crown Castle Site Plateau Park off Blandford St COLLAROY PLATEAU Broadcast/Comms (Optus) Tower Sydney Water Board Site off Plateau Rd BILGOLA PLATEAU Broadcast/Comms Tower Rooftop Tower 1 GCA Building 1 Lawson Square REDFERN Broadcast Monopole Aust Radio Network Site 754-768 Hawkesbury Rd HAWKESBURY HEIGHTS Crown Castle Site Badgelly Hill off Badgally Rd GREGORY HILLS Canberra and Darwin currently have limited “experimental” transmissions 40  Silicon Chip      (source: ACMA) siliconchip.com.au available from plumbing supply stores but it is expensive and not easy to work. Centre-punch the boom for all holes prior to drill­ing. The boom is 1250mm long and the total of the element spacings along the boom is 1100mm – see the plan diagram on Fig.1. Mark the hole centre position for the reflector element first, 125mm from one end of the boom, and then work your way along. If you have a drill press which lets you drill all the element holes square through the boom you are fortunate. If not, mark the hole centre positions on both sides of the boom and drill from both sides. If you don’t get the element holes lined up properly, you will have the elements skew-whiff. A few words of advice on drilling is appropriate here. Drilling in thin wall aluminium tubing can be a problem and many people tend to end up with holes that are more triangular than round. The way around this problem is to drill all the large holes (ie, all 10mm holes) under size and then ream them out to the correct size using a tapered reamer. Don’t drill the larger diameters with too high a speed otherwise there may be a tendency to produce “triangular” holes. If you have a bench drill which allows you to set slower drilling speeds, so much the better. Either way, it is best to drill the element holes to 10mm and then slightly increase each hole with a tapered reamer so that each element is held firmly in the boom. Reaming larger holes Be careful when reaming holes out though because it is quite easy to get carried away and then end up with holes that are oversize. Use a scrap piece of 10mm tubing to test when the holes specified at 10mm are the correct size. Each director element and the reflector is held in the boom with a selftapping screw, as shown in diagram A of Fig.1. Drill a 3mm hole at the centre point of each element but only through one side. Don’t mount the elements on the boom yet though because the dipole should be assembled and mounted on the boom first. You need to keep a mental image of how the finished antenna will appear. All the directors, the folded dipole and the reflector will all be vertical (ie, perpendicular) but the holes siliconchip.com.au for the clamp, at the reflector end of the boom, will be horizontal. Confused? Take another look at the photos of the finished antenna. Now cut the 10mm diameter tubing for the director, three reflectors and parts for the dipole. Remember the old adage about “measure twice and cut once”. It’s hard to lengthen elements that are too short. Note that two of the directors are the same length, ie, 670mm while the other is 664mm. Making the dipole The folded dipole is made from five pieces of 10mm alumini­ um tubing, three long and two short. The detail of its assembly can be seen from the diagram at the bottom of Fig.1. The two short tubes, shown as diagram E on Fig.1, are cut and shaped so that they key in with the top and bottom elements of the dipole. Further detail is shown in the accompanying photos. The top and bottom pieces of the dipole are held at each end with a 60mm long M4 screw (or 3/16-inch Whitworth), together with a nut and lock washer. At the centre, the lower halves of the dipole are terminated on an insulating plate (shown in dia­gram D of Fig.1). This plate is made of 3mm acrylic (Perspex or Lexan). The dipole halves are each secured to the insulating plate with a 19mm long M4 (or 3/16-inch Whitworth) screw, nut and lock-washer. Terminals for the dipole are provided with two 32mm long M4 or 3/16inch Whitworth screws, each fitted with a nut and lock-washer plus a wing nut and flat washer. The insulating plate is secured to and spaced off the main boom via a 19mm length of 19mm PVC conduit, shown as a “folded dipole spacer” in diagram F of Fig.1. The top piece of the dipole is secured to the boom with a 60mm long 3/16inch Whitworth or M4 screw, nut and lock-washer The details of the dipole insulating plate and fixing to the boom can be seen in the accompanying photos. Note that while we used white Perspex, you could use a piece of polycarbonate if that is what you have on hand. However, note our remarks on painting, later in this article. By this time the antenna looks just about complete. You need to add the antenna clamp, to enable it to be attached to the mast. This must be Parts List – DAB+ Antenna Aluminium 1.25 metres of 19mm square tubing with 1.2mm wall thickness 4.5 metres of 10mm diameter tubing with 1mm wall thick­ness Hardware 1 120 x 40 x 3mm white Perspex 1 stainless steel or galvanised U-bolt and V-clamp to suit mast 4 8G x 13mm self-tapping screws 3 M4 x 60mm or 3/16in Whitworth screw (round head) 2 M4 x 32mm or 3/16in Whitworth screws (round head) 2 M4 x 19mm or 3/16in Whitworth screws (round head) 7 M4 or 3/16in nuts 2 M4 or 3/16in wing nuts 7 M4 or 3/16in lock washers 2 M4 or 3/16in flat washers Note: all screws, washers and nuts should be AS316-grade stainless steel 1 19mm long spacer cut from 19mm conduit or similar Miscellaneous (sizes/lengths to suit) Mast and wall mounts or barge-board mount (hockey stick style) 300Ω to-75Ω in-line balun (Jaycar Cat LT-3028 plus matching F-connector) Quality 75Ω coax cable (Jaycar WB2006/9, Hills SSC32 or equivalent) Plastic cable ties Silicone sealant mounted at the end of the boom (ie, behind the reflector) and oriented to allow the elements to sit vertically. You will also need a 300Ω-to-75Ω balun to match it to 75Ω coax cable. You could use 300Ω ribbon if you wish and omit the balun but to obtain the most interference-free signal, we recom­ mend coax cable for your installation. Unfortunately, many antenna clamps are sold with a cadmium-plated and passivated finish (which look like a “gold” finish). This is barely adequate for inland areas but rusts quickly in sea air. We may seem to be paranoid about corrosion but since the SILICON CHIP editorial offices are only a kilometre or so from the seaside we are very aware of just how quickly metal hardware can rust and corrode. November 2015  41 Connecting your DAB+ Antenna   OK, so you’ve finished your DAB+ Yagi and now you’re ready to connect it to your receiver. Most DAB+ tuners do have an antenna input socket, so that makes it easy. But the vast majority of DAB+ radios (especially the smaller ones and virtually all portables) are not equipped with any form of antenna input, apart from the whip antenna. So how can you connect an external antenna? What are the connection options? The V-block/U-bolt clamp should ideally be stainless steel or at worst hot-dip galvanised (don’t use Cadmium-plated [or “passivated”] steel – you can see them rust before your eyes!). It must mount between the reflector (seen here on the right) and the end of the boom, so that the mast doesn’t interfere too much with signal. Note the orientation – it mounts so that the elements are vertical when the clamp is attached to the mast. If you can, buy U-bolts and clamps that are stainless steel, as used for car exhaust systems (or boat fittings), as these will last a lot longer. At minimum, choose hot-dip galvanised. Be aware that zinc “plated” fittings are not as rust resistant as galvanised types. Zinc-plated fittings have a smooth bright appearance while hot-dip galvanising is unmistakable – it has quite a rough appearance. We also suggest that the ends of all the elements and the boom be stopped up with silicone sealant. This will stop them from whistling in the wind. (Commercial antenna manufacturers tend to squash the ends flat for this purpose). Better still, you can buy Delrin plugs to suit the square aluminium tubing. These look neater. If you live in an area where corrosion is a problem, it is also a good idea to paint your antenna. If nothing else, the dipole insulating plate should be painted as acrylic material does deteriorate in sunlight (ie, UV). We suggest you leave the antenna for a month or so to weather it and then paint it with an etch primer. Finish it with an aluminium loaded paint. Installation When you have finished your antenna you need to carefully consider its installation. There is no point in going to a lot of trouble making it if you don’t install it properly. Try to install your new antenna well away from existing TV antennas as these can have quite a serious effect on the perfor­mance. Similarly, nearby metal guttering, electric cabling, metal roofing or sarking (ie, reflective insulation such as Sisalation) can have a bad effect on antenna performance. And don’t forget the effect of a hot water tank which may be lurking just beneath the roof tiles. If you live on a busy street, try to install your antenna as far away as possible from the traffic side of your house. That will help minimise ignition noise from passing traffic. Finally, install the antenna as high as possible above the roof and guttering. If that is a problem, try to install 42  Silicon Chip The antenna (and the coax lead in) require a connection to both the antenna input and earth. And with very few exceptions, there is nowhere on the outside of the case to get an earth connection. So you need to install a socket on the back of the receiver which the cable from the antenna could be plugged into. Fitting a socket Open up your receiver and find an appropriate place to mount a socket. While the back panel of our receiver is quite spartan, inside the possible locations are limited by existing fittings and hardware. Two main points to watch when choosing a location are: (a) mount it as close to the receiver’s input terminals as possible to keep your input wires as short as possible (we are using ordinary hookup wire, not coax); and (b) check inside the receiver to make sure the mounting position will not foul any internal hardware – and that you have enough room to fit any washers/nuts to hold the sockets in place. The type of socket is up to you – those receivers which do have input sockets often use standard 3.5mm “audio” types because they’re nice and small. However, we elected to use a standard “Belling Lee” socket (sometimes called a “PAL” socket) as used on TV antennas, mainly because it seemed appropriate to use the “normal” plug/ socket for 75Ω coax. Fit the socket first, then wire the connections to the receiver. We chose to connect to the bottom end of the whip antenna mounting rather than the receiver’s PCB because it was the shorter connection; the “braid” connection from the socket connected to a solder lug under the same self-tapping screw which connected the receiver’s ground plane. We couldn’t find a solder lug large enough to fit under the antenna mounting, so effectively made one by winding a double loop of hookup wire about 7mm in diameter and applying solder to that, making it rigid. We were fortunate when we removed the nut holding the whip antenna in place, there was plenty of “meat” left on the thread to allow our “solder lug” to fit on as well. Our photographs explain all this in detail. siliconchip.com.au   to your DAB+ Receiver Opening just about any DAB+ receiver will reveal a PCB containing the DAB+ receiver module (the silver box middle of lower pic) with whip antenna connections close by. We elected to attach our external socket to the other end of the antenna cable because it was simpler. The photo below shows an enlargement of the area where we located the antenna socket. Be careful that you allow enough room for the socket and for its mounting screws – ours will end up very close to that vertical pillar. And here is that antenna socket, wired into the mounting hardware for the whip antenna (the blue wire) and to a solder lug connecting to the ground plane and the antenna wire braid (green wire). We used ordinary hookup wire to make the connections. siliconchip.com.au Finally, here is what the antenna socket looks from the outside. We used a standard Belling-Lee connector, just as you would find used on the antenna socket on most TV sets. A matching plug was wired to the end of the coax cable coming from the new DAB+ Antenna. November 2015  43 the antenna so that it is at least a half wavelength away from the nearest metallic object such as guttering or roofing. This means a distance of about 750mm away from guttering. Take care when installing the antenna. Safe working with ladders is particularly important. Take your time and don’t take risks. You don’t want to end up in hospital. Line up the antenna so that it is aimed at the closest DAB+ transmitter. As you can see from the table on page 40, they can be fairly widely separated but all contain the same stations (in a geographic area) so simply aim at the one that is either closest to you, or the one that gives you best performance (eg, minimal errors shown on the DAB+ station readout). More often than not, they will be the same transmitter. Choosing coax cable You probably know that there is a wide range of prices for coaxial cable, ranging from cents per metre to dollars per metre. What’s the difference and why is it important? When it comes to coax quality, price is usually a pretty good guide. Apart from the coax impedance (you want 75Ω), the main criteria you look for is attenuation, or loss. Unfortunately, all coax is lossy – this means that even if you get the last microvolt of signal from your antenna, depending on the quality of the coax lead, some of it/a lot of it/most of it can be lost on the trip to your receiver. As a matter of interest, when we were checking out the performance of this antenna, we were getting diabolically bad results. It turned out that the length of coax cable was crook – really crook! Swapping to a new length of cable gave us the results we were expecting (actually better – but we would say that, wouldn’t we!). Cheaper coax has a solid plastic dielectric, mid-range has an extruded pattern which is mostly air (hence “air-core”); the best domestic coax has “foam core” dielectric, (which has minimum loss) and the outer conductor is not only pretty tightly woven (for minimum loss) it also has one or more levels of aluminium foil surrounding the copper mesh (for minimum loss AND to minimise interference!) Attenuation is expressed in dB/100m and increases as frequency increases. Because we’re not talking super high frequencies (~200MHz) you can be a bit less fussy in selecting coax. But really, if you’re making this antenna because you need all the signal you can get to avoid the digital cliff – and especially if the length of coax lead-in needs to be relatively long – buy the best coax you can afford, within reason. When the antenna is mounted on its mast, make sure the coax is firmly secured to that mast (and to the antenna boom) with cable ties, otherwise the cable can flap around in the wind. There is nothing more annoying than lying in bed late at night and listening to the cable slapping against the mast! Cable ties are cheap: use them! Performance Before conducting any measurements, we hooked the Yagi up to a “generic” DAB+ radio in a known very poor signal area – Narrabeen, in Sydney’s northern beaches area. In fact, until recently there was no DAB+ in Narrabeen. The “new” Collaroy Plateau transmitter has alleviated this to some extent but our test location is deep under the plateau escarpment – anything but line-of-sight. What a difference! The Yagi pulled in quite a few stations which were simply not there before; of those that were, signal levels were much improved. Then, to prove the performance of the DAB+ Yagi, we took a number of spectra using the Signal Hound Spectrum Analyser (as reviewed in the October 2014 [siliconchip.com.au/Issue/2014/ October/Signal+Hound+USBSA44B+Spectrum+Analyser] and June 2015 [siliconchip.com.au/Issue /2015/June/SPIKE%3A+Improved+S oftware+For+The+Signal+Hound]issues). Two of these graphs are shown on page 38 – they confirmed our first tests and demonstrate that the new antenna has a gain of around 12dB with respect to a whip antenna – that’s pretty good and well worth the investment! SC Radio, Television & Hobbies: the COMPLETE archive on DVD YES! A MORE THAN URY NT QUARTER CE ICS ON OF ELECTR HISTORY! This remarkable collection of PDFs covers every issue of R & H, as it was known from the beginning (April 1939 – price sixpence!) right through to the final edition of R, TV & H in March 1965, before it disappeared forever with the change of name to EA. For the first time ever, complete and in one handy DVD, every article and every issue is covered. If you’re an old timer (or even young timer!) into vintage radio, it doesn’t get much more vintage than this. If you’re a student of history, this archive gives an extraordinary insight into the amazing breakthroughs made in radio and electronics technology following the war years. And speaking of the war years, R & H had some of the best propaganda imaginable! Even if you’re just an electronics dabbler, there’s something here to interest you. Please note: this archive is in PDF format on DVD for PC. Your computer will need a DVD-ROM or DVD-recorder (not a CD!) and Acrobat Reader 6 or above (free download) to enable you to view this archive. This DVD is NOT playable through a standard A/V-type DVD player. Exclusive to: SILICON CHIP 44  Silicon Chip ONLY 62 $ 00 +$10.00 P&P Order now from www.siliconchip.com.au/Shop/3 or call (02) 9939 3295 and quote your credit card number. siliconchip.com.au