The MW DX Challenge
Intro: This article was first penned in 2002. Since then, the threat to DXing as we know it from digital audio broadcasting (DRM) has failed to materialise. DRM (Digital Radio Mondiale) has succumbed to alternative digital delivery methods, namely satellite, DAB (VHF Digital Audio Broadcasting) and internet broadcast feeds. Back then we speculated about the ‘bells and whistles’ that digital would bring, what sort of interference we would have to contend with and whether DXing as we know it would survive, how would we fare in the short term and if we could still DX analogue signals in the midst of the digital revolution.
DRM has slipped from being a New World high-quality mode supported by the mass release of DRM receivers by all and sundry to its current status as a poor cousin to streaming high quality feeds for rebroadcasting by other stations and as a novelty for the odd hobbyist simply wanting to try something new. For example, the purpose of Radio New Zealand International’s DRM broadcasts is largely to send programming to stations ion the Pacific for local MW & FM dissemination.
For years now the news for New Zealand MW DXers hasn’t been good, which is a reflection of the scene globally though with its own ‘Kiwi” twist. More and more stations and formats are entering the market (which seemed saturated as it was), with 24-hour broadcasting by all and sundry and national networks setting up stations in every town and city. These factors along with the advent of ‘Access Radio’ stations offering an outlet to minority interest groups has resulted in a plethora of stations inundating the MW band.
The only good news for NZ MW DXers in recent times was that our government would not allocate channels in the extended band (1602 – 1701kHz) thus leaving it free for DXing foreign stations (and it has been a catalyst for renewed interest in MW DXing too).
FM – Saviour of MW DX – NOT!
For the last 2 decades, the attraction of the superior audio quality of FM has often seen stations sacrificing the coverage of AM to obtain the better dynamic range and frequency response that FM offers. Many new stations have gone straight to FM and given MW little consideration. Also, its generally cheaper to establish an FM station from an aerial point-of-view… no large tract of land is required to place a tower and radials upon as an FM aerial needs to be little bigger than an average VHF TV aerial.
So we could be forgiven for thinking that given the advantages, savvy broadcasters would switch off their MW frequencies and leave a band will plenty of gaps for the aspiring MW DX to pursue their hobby. Wrong. What we have seen is that the networks have moved their music stations to FM and filled the vacant frequency with largely talk back and sports channels. On top of that, many stations have chosen to retain the same programming on both MW & FM, e.g. National Radio. End result, there are consequently fewer gaps in the bands than 10 years ago…
The Revenge of the MW DXer – Part One
So MW DXers need to combine both proven techniques and employ new technology to their benefit.
Whether you DX from home or a remote site, your equipment needs to give you the edge.
O.K…. so they’re essential piece of equipment, but what do you need to make all the effort you’ve put into aerials, using up valuable brownie points so you can have aerials in the flower garden, finding a DXpedition location, extra equipment etc? A receiver that will maximise your chances of hearing those weak, distant signals.
There are numerous figures and specifications provided by manufacturers and test panels which will point you in the right direction towards a DX dream-machine. If were to purchase a receiver for the prime intention of MW DX, the factors I’d be most interested in are:
In the crowded MW band where stations are separated by as little as 1kHz, the ability of the receiver to discriminate between adjacent stations and to provide loggable audio is essential. What’s more the width of the filter’s skirt is as important as its quoted width and is often determined by the type of material the filter is manufactured from. For example, ceramic filters have very wide skirts allowing interference to ingress whereas mechanical or crystal filters provide very sharp skirts. Look for a receiver with a filter of around 2.5kHz at –6dB and a skirt width of less than 5kHz at –60dB (the narrower the –60dB figure in relation to the –6db the better – don’t worry too much what that means, just use it as a point of comparison between receivers).
If you’re tossing up options at purchase time, between a VHF converter, external speaker or a sharper filter, take the latter!
Some receivers aren’t designed to apply all of their features to MW and sensitivity is often affected by internal attenuation to prevent strong local signals over-loading the receiver. In many receivers the attenuation can be readily set to zero by a front-panel control, or a simple software fix. In others, (e.g. Kenwood R-5000) it’s a soldering iron job which, given the complexity of modern receivers, not all will be keen to tackle.
Generally useful devices that may be handy for giving a weak signal that extra nudge.Pre-amps that do not degrade the signal-to-noise ratio are extremely useful, though often they have been disabled on MW or require a user software fix to be enabled. Check to see if they will work on the MW band or can be adapted to do so.
Some may consider having a receiver with 400 memories as more than sufficient, though for the MW DXer, the ability to program in every MW DX channel in the best mode, with the optimum filter setting etc. is a real bonus. This allows swift tuning between channels which in a strong opening is very handy for analysing the best frequency(s) to monitor.
And there’s little point in erecting long aerials, spending heaps on coax, preamplifiers, tuners, baluns etc, if the weak signals you’re chasing can’t be heard under the receivers internal noise! A simple test to see how noisy a receiver is, remove the aerial and turn the volume right up… should be very quiet, a low-level background noise, ideally the noise level would be near zero and you would hardly notice the volume had been increased. I’m fortunate to have an ultra-quiet 25 year old Drake SPR-4 that has allowed reception of weak signals at loggable levels, which have been buried on colleague’s receivers.
Modern receivers with all their synthesisers, microprocessors and fluorescent displays can produce a fair amount of internal noise. This can effect the use of indoor loop antennas near the receiver, as they’ll pick up the noise radiated from the electronics. Another simple test is to hold a transistor radio about 50 cm from the set and see how much hash it picks up.
Noise Blankers, Notch Filters and Digital Signal Processing
All very useful tools to have. Most noise-blankers will deal to electric-fence noise whilst notch filters will eliminate steady whistles and DSP will clean up all manner of band noise.
Operating Voltage/Current Consumption
If battery operation is required (for example when running mobile or on DXpeditions) the amount of power drawn by a receiver will dictate how long a battery will last (and if you can start the car after a nights DX!). The Drake R-8A uses 2 amps when running (i.e. 30 hours operation on a fully charged car battery) though the drop in voltage will see the set turning itself off well before the 30 hours are up and 1 amp switched off on the front panel. The consequences of high battery drain mean that you’ll need to be prepared for long stints at the dials by bringing extra batteries or charging between uses.
Most receivers are designed to work off 12 or 13.8 volts DC so a well-regulated power supply or battery will be needed.
Most receivers come equipped with the facility for 1 x 50 ohm input and 1 x 600 ohm input aerial with front-panel switching. I’d prefer to see at least 3 x 50 ohm inputs to allow ready access to a range of aerials.
If you’re looking for a new receiver, there are a number of models currently available that are hailed by DXers as good MW DX machines. Here is a list of known good performers.
AOR: AOR7030, AOR 7030+
Japan Radio: NRD535D, NRD545D
Icom: IC-R70, IC-R71E, IC-R75
Drake: SPR-4, R8, R8A, R8E
Kenwood: R1000, R5000
Palstar: R30A, R30C, R30CC
And some ham transceivers are available at very reasonable prices…
Icom: IC-706MK2G, IC746PRO
Kenwood: TS50, TS480, TS2000
Tentec: RX320, RX321, RX330, RX330, RX340
And software defined receivers:
Flex: 3000, 5000
Another option worth exploring with many radios to make them really top performing sets is to purchase one modified by Sherwood Engineering. For not a lot more than the purchase price, Sherwood can ‘hot-rod’ several of the above.
You can’t beat a Beverage.. but then very few of us have 300m or more for them.
Fortunately, there have been many developments in compact receive antennas that will fit in the smallest yard. Hard Cord DX have articles on K9AY, EWE, Pennant and Flag antennas. They are easy to construct and will benefit greatly from a preamplifier. Advanced Receiver make such a device with their P0.1-30/20VD unit.
There are several types of headphone worth considering. Headphones manufactured with the hi-fi market in mind reproduce high levels of bass and treble. They give excellent frequency response and provide pleasant listening to high-quality music. Great for music and often suitable for DXing, though there is another option.
A MW DXer generally isn’t too interested in high-fidelity, the frequencies covered by the spoken world are more crucial and there are several headphones that emphasise that frequency range. These are manufactured for the amateur radio and DX fraternity by the likes of Kenwood and Icom. They reduce the amount of bass and therefore rumble and reduce the amount of treble, which will soften heterodyne whistles and reduce hiss.
If you are DXing with others, and particularly on a DXpedition, you’ll need a pair of enclosed muff phones to prevent what you’re listening to annoying others. There are noise-cancelling headphones which form an electronic noise-barrier to prevent external noise affecting your listening. Sony is one manufacturer of these surprisingly effective devices.
It’s also important that you have a good tape recorder to capture as many of those often fleeting moments of reception as possible. Some DXers leave the recorder running non-stop, others hit the record button as soon as something interesting pops up.
And recording media now comes in many forms and prices.
Audio cassette recorders, Hi-Fi video recorders, digital audio tape and mini-disk recorders have all been useful in the past, just there is better technology available, i.e. MP3 recorders. No tape or disk is required as the audio is recorded onto a computer chip. They’re numerous and very reasonably priced. Bjarne Meld has written an excellent article on them from a DXer’s perspective.
A little trick when using stereo recorders. Feed the audio from your main receiver into one channel and audio from a second receiver tuned to WWV into the other. That way you’ll be able to have a time-base accessible by playing the tape back through an amplifier with a balance control. (Thanks to Andy Gardner!)
Phasing units, which allow the combination of signals from two antennas to reduce/remove interference or noise and to increase gain by adding signals together, have always piqued the MD DXer’s interest.
A couple of manufacturers are supplying units, which have caught the attention of the DX-fraternity, namely MFJ Enterprises MFJ-1025 and MFJ-1026 and Timewave’s ANC-4, are producing moderately priced units. They even give you an advantage with shorter aerials.
With these units deep, stable nulls on a variety of signals make it possible to totally remove interfering stations and open up a whole new world of possibilities. I use mine as much for increasing signal gain by phasing two aerials together as I do dealing with QRM.
These commercially available units were intended primarily to cancel noise, yet have shown their real value in reducing interference and enhancing signals using signal inversion and phasing. For user reviews, check these articles:
There are other items that the MW DXer may find handy in the pursuit of weak signals, particularly on DXpedition when accompanied by colleagues.
When using modern sets with low-impedance inputs (e.g. the SO-239 connectors on 99.99% of DX comms receivers) connected to high impedance aerials (e.g. Beverages) an impedance matching device (commonly known as a balun) is required to maximise signal transfer between the two. Baluns are best installed some distance from the receivers and fed with coax to prevent interaction. It is also a good idea to keep aerials separate as they approach the listening site (e,g, not anchored on the same pole) for the same reason.
When you’re fortunate enough to have a number of aerials to choose from, an aerial switch will be required. Ideally they should be metal-encased and offer high isolation between aerials to prevent interaction. For receiving, cheap coax switches are just fine.
On DXpeditions when DXers are sharing an aerial, a splitter is required to provide equal signal levels to all sets. Standard splitters will cause a small signal loss so a preamplifer may be required. John Bryant who sadly is no longer with us, penned this excellent article on splitters. The Mini Circuits 2-way and 4-way units are known performers and work very well with broadband amps.
And when you’ve finally found that ultra-quiet environment, a preamplifier may help you drag a signal out of the mud. It is important that the amplifier has a very low level of internal noise otherwise it will also bury the signal. Make sure the preamplifier has excellent signal-to-noise figures. An good unit would have a gain of 10 – 20dB and a noise figure of around 2dB. Also make sure they work down to 0.5mHz (500kHz) as a lot of preamps are designed for above 1.8mHz.
BHI manufacturer noise-cancelling speakers which offer the opportunity to clean up noise and deliver copy from an otherwise unintelligible audio clip.
DXpeditionsDXpeditions are the solution for urban DXers trapped in a noisy environment, lacking the real estate for erecting long aerials and yearning after a DX-fix. The solution is to find an electrically quiet environment (preferably near the sea) where aerials can be installed without threatening life (human or fauna). And some DXers go to extreme lengths to obtain these requirements, for example the Scandinavians who frequent Lemmenjoki in the Finnish Arctic Circle and suffer the extremes of weather conditions.
Because DXpeditions are often in remote, electrically quiet conditions, a mains power supply may not be available, with the nearest power-pole some distance away (hence the need for battery-operated receivers and tape recorders). Other non-existent luxuries like hot water, telephone (& internet) connections and nearby shops make planning important. In such circumstances the DXers ingenuity is challenged as everything from cooking meals to charging batteries to staying clean and staying in touch becomes a consideration.
Sleep-deprivation, bad weather, lengthy journeys and all the other ‘negatives’ are usually more than off-set by the quality of the reception, the chance to experiment with aerials, receivers, splitters etc and above all by the comradeships formed. Days are spent collecting firewood, the odd aerial maintenance chore, recounting the previous night’s experiences, tales of ‘the one that got away’ or sleep (MW DX is best at night so the candle often gets burned at both ends and in the middle too!).
And a successful DXpedition usually doesn’t end when you’ve arrived home. There will be numerous reception reports to write and magazine articles to prepare (having a lap-top on the DXpedition is a great idea!).
Top DX Sites abound in New Zealand. There are plenty of wide-open spaces and huge amounts of coast to explore.
Choosing A Site
There are numerous factors to consider when looking for a site. Ideally, it should be in a remote area, away from nearby power-lines, miles from the nearest MW/LW transmitter, close to the sea, having a comfortable place to stay and large enough for long aerials.
Remote areas usually mean farmland. Ideally flat ground with the odd tree to assist erecting aerials. The presence of fences can be handy though a note should be taken that even with all-wooden posts, the chemical treatments to prevent the posts rotting away (eg. tanalising) leaves them conductive (albeit with a relatively high resistance but a concern nonetheless). If you’re going to use a fence, either insulate the wire wherever it touches the posts, or run a separate wire along the top.
In New Zealand, the preponderance of electric fence units can ruin an otherwise promising site. A quick check with an AM radio listening for tell-tale clicking is a good test. Electric fences are usually their noisiest during a dry period and a good rain fall lowers the level of noise by improving their ground conductivity and washing insulators tracking high voltage across dusty paths. Electric fences are generally only found on stock farms so other rural land uses like extensive horticulture may offer a lower noise level than in a dairying area. As mentioned above, receiver with a good noise-blanker or an external noise-blanker will eliminate the “ticks” even in areas with a preponderance of electric fences.
Overhead power lines, particularly high voltage varieties should also be avoided. If the choice is between a quiet, battery-powered DXpedition and an “all the comforts of home” mains-run version, I’d take the former any day! Noisy power lines also benefit from a good rain to clean insulators etc. Underground power supplies are a good deal quieter as there is no exposure to the elements to cause noise (and they’re fairly deep as those poles are quite long!).
And the further away from MW & LW transmitters the better as well. Even with directional aerials, locals will be a pest though you’re invariably going to be better off than DXing from home. Other possible sources of RF interference like non-directional beacons (marine and aeronautical NDBs), GPS stations and the like should be checked too.
A site close to the sea is also a benefit. Absorption of signals by ground attenuation is more pronounced the further inland you go. So saying, the very successful Beverage site at Waianakarua is 7km from the coast and reception there is very good.
When To Go
Best months for DXpeditions are around the Autumnal and Vernal equinox, which are late March and late September respectively in the Southern Hemisphere, the opposite in the Northern Hemisphere). Reception from near-polar paths is best around these times though good signals on mid-latitude paths also occur in January/February and October/November.
If you’re into long-term planning, the lowest point of the solar cycle is also the time to chase signals. That means 2016 through 2019 will be prime DXpedition years.
If a mains-free DXpedition is planned, consideration to the type of battery is important. For short duration trips, a standard 30 – 60 amp-hour car battery may suffice, though for longer stays or with multiple receivers sharing the same power source, a deep-cycle battery is highly recommended.
These units are often used for back-up power supplies or where reliability is crucial because of their ability to provide a constant voltage under heavy current drain for a considerable period of time.
Whilst more expensive, they are undoubtedly good value given their suitability for running 3+ sets at once. Ratings of at least 85 amp-hour would be the minimum and 120 amp-hour suggested.
If you’re operating on 12 volts, a lighting system that provides maximum light output and minimum battery drain is essential. The answer is LED lighting which has become very reasonably priced. A 7-watt unit over head gives excellent light and less than the dial-lights on many receivers!
LED head lights are also very useful, especially if they can be dimmed.
You can maximise your MW DX success and enjoyment by following the above recommendations as much as possible. Effort will certainly be rewarded.
So good luck and good DX!