I’ve been asked a seemingly simple question: How do you DX mediumwave stations? Well, the answer proved more complicated that at first thought and worthy of sharing, so here goes!
Let’s first look at what you’ll need for a typical DX session.
Receiver:
It’s not just a matter of using any rig proclaimed to be a “DX machine” and flicking around the MW band! Because you’ll be ferreting out signals in the presence of New Zealanders as little as 1kHz away, you need a receiver with excellent selectivity (i.e. the ability to provide the desired signal with a high degree of protection from adjacent signals). This requires a receiver with a narrow IF filter, something a bandwidth close to 2.4kHz and ideally with a shape factor of 1.6 or less, typically a crystal filter. To define the shape factor in layman’s terms, think of the filter shape as resembling a mountain, with a narrow, flat top and steep sides. The narrow peak is the bit that is ideally around 2.4kHz and the steeper the walls the better the shape factor and greater the ability to separate adjacent stations. Many receivers are fitted with ceramic filters, some around the 2.4kHz mark, though the flatter wall slopes on these filters will not suppress strong adjacent signals as well as a crystal filter. A number of receivers have narrow filter options that are only selectable in SSB mode, that’s fine; the fidelity may not be as easy on the ear as AM mode and you will be confronted with whistles as you zero-beat signals but you can still work DX very satisfactorily.
Rather than tune MW in AM mode, by tuning in SSB, you can also select the best side-band for the situation, e.g. if you’re on 1070kHz and the interference is coming from 1071kHz, use Lower Side Band. Similarly if you’re on 1360kHz and the interference is coming from 1359kHz, use Upper Side Band.
If you have a receiver with multiple memory channels, you can program the best
sideband for each frequency (you’ll need 117 memories for each 10kHz channel of the MW band between 530 and 1700kHz).
Distant MW signals are frequently very weak; therefore you’ll need a sensitive
receiver, ideally one that can successfully provide an audible signal from stations that hardly move the S-meter.
Recommended models are (in no particular order): Drake models R8, R8A, R8B, AOR models AR7030, AR7030+, Kenwood R5000, Japan Radio models NRD535D, NRD 545, Drake SPR-4, Icom models IC-R71A, IC-R71E, IC-R75. If you’re on a budget, look no further than the Palstar R30, and if price is no impediment the Ten Tec RX340 or Watkins Johnson HF1000.
A word of warning: some “high-end” receivers are down-graded by their manufacturers for MW use, ostensibly to prevent strong nearby mediumwave signals from overloading the set. This is accomplished by building in signal attenuation. In a number of cases, removing the attenuation can be easily performed by a competent soldering-iron wielder (e.g. Kenwood R5000) or by using a manufacturer’s solution to over-ride the factory setting. Similarly, many sets have preamplifiers, which are very useful on SW though disabled on MW; again, there are often ways around this problem too.
Aerials:
Ideally, you need a Beverage antenna. Something at least 300 metres long, between 2 – 4 metres high, pointed at your target area, terminated to ground via a resistor of approximately 470 -560 Ohms at the far end, and fed with coax and an impedance matching transformer. There are few alternatives that come even close to a Beverage for MW DX.
If you don’t have the real estate for such a device, there are a number of aerials that take up a lot less room and deliver superior results to a random wire antenna. Slopers, K9AY, EWE, Kaz, Flag, Radial Wire and Pennant aerials all have directional properties and are worth exploring. Some of these will fit in an average back yard. More information can be found on the internet or in antenna handbooks. Even a simple half-wave dipole, fed with an impedance matching transformer and coax in an electrically quiet environment can produce reasonable results.
Earth:
Make sure you go to the trouble of installing a good earth system. If you’re fortunate to listen in an area where the soil has a high moisture content, a single earth rod is probably all you’ll need. If your soil is dry or rocky and has little moisture retention, you’ll need to go to more trouble, i.e. several earth rods, a buried wire, metal mat (copper is best), buried coax etc etc.
Another trick is to connect another aerial in place of your earth wire. This can be particularly advantageous if your earth is electrically noisy.
If you’re listening from a place supplied with mains power, make sure your earth rod is well apart from the mains earth, otherwise interference being bled to ground via your mains may be picked up by your receiver’s earth.
Coaxial cable:
You can pretty much use any cable, whether it’s 50 or 75 ohms and at MW frequencies, signal loss is negligible. I know of one DXpedition that ran 200 plus metres of coax to an aerial and achieved good results. If cost is a factor, then RG59 TV coax will probably be your best option. If you want to buy 50 ohm coax, go for RG58C (the one with just copper braid, i.e. not an additional aluminium foil) and if money’s no object, RG213 50 ohm coax.
Tape-recorder:
If you’re using a tape-recorder for DXing, it should be AC/DC powered, have a tape-counter (essential), an earphone outlet and a mic recording jack (preferably a line-in connection). When running away from the mains, use alkaline batteries as they provide a good operating life and won’t leak if left unused for some time. When you first put a new tape into the unit, set the counter at zero and jot the counter reading down against the time and event, e.g
031 0435:30 Station ID and commercial for Mortgage Wizz
034 0436:00 Song introduced, Dr Hook “Sylvia’s Mother”
038 0439:30 Announcer gives time, id and weather brief.
Some DXers leave the recorder running all the time, this means they never miss recording what they hear, though does mean quiet a bit of editing later to skip songs etc.
After using portable cassette tape-recorders for many years, many DXers now prefer the mini-disk option. Mini-disks offer many advantages, namely -no loss of original recording even after multiple replays, quicker access to tracks (almost instant slipping between recordings).Mini-disks also automatically create an index point for every recording., e.g.
01 0435:30 Station ID and commercial for Mortgage Wizz
02 0436:00 Song introduced, Dr Hook “Sylvia’s Mother”
03 0439:30 Announcer gives time, id and weather brief
More On Mini-Discs
Blank recording media:
If using audio cassettes, C60s are recommended as they are less likely to cause problems than C90s and less time spent rewinding/fast forwarding.
Timer:
Preferably, with a seconds display and an alarm for early-morning excursions. A dual-time option to display local and UTC time is very handy.
Log-book:
There is a wide choice of material to use. School exercise book with ruled pages are eminently suitable and very cheap at around 40c each. The tape/disk number is written in the left-hand column and station on the left hand page, with announcements transcribed onto the right hand page. As a suggestion, number the books themselves sequentially and have the start and end dates on the front cover.
As we’re dealing with domestic stations primarily, I don’t use the SINPO code to describe reception conditions. Most MW broadcasters wouldn’t know what it was and due to the non-repetitive nature of many DX catches, there’s little point in telling a distant station what conditions were like. It’s better to give them a comparison between their signal and others in the same geographical area.
Headphones:
Go for full ear muff variety, not open-air (especially if you don’t want to share your listening with others). Make sure the band isn’t too tight and that they’re going to be comfortable to wear for hours on end, i.e. have soft padding. Good quality ‘phones produced by hi-fi brands such as Pioneer, Sony, Technics etc will do the job admirably though if you want the best, go straight to Sennheiser. Make sure the pads are large enough to cover your entire ear or they may become uncomfortable.
Patch cord:
That’s cable that connects your receiver to your recorder. If you’re making your own cable, don’t scrimp with el-cheapo wire, use good quality shielded microphone cable. Note: the line output level of most receivers will connect directly to the line input of a mini-disk recorder, however, if you’re connecting the receiver into a mic input and your receiver doesn’t have a variable line output level, then you’ll need a patch cord with signal-dropping resistors to match the two together.
Reference material:
World Radio TV Handbook
Passport to World Band Radio
Atlas
Language dictionaries etc
Sunrise/sunset plotters (e.g. Xantek’s “DX Edge”) for determining likely signal-paths, fade-in and fade-out times.
Target lists:
Here’s an idea; maintain a list of target stations and update it periodically. A good media is a computer spread-sheet with worksheets for time blocks, e.g. 0200 – 0400, 0400 – 0600, 0600 – 0800 etc. Each sheet can then be printed out and taken on DXpedition with you.
You can also use lists of wanted stations, countries, states, etc with columns for frequency, time etc and all sortable by any of the columns. Because MW DXing is a lot more random than SW, it’s difficult to plan what you’re likely to hear in any great detail (and that can be the great thrill of MW!).
I’ll define my target lists by keeping note of what other Dxers have heard or by type. Typically unheard US States, unheard countries, wanted stations etc, sorted into geographical regions. Then if propagation favours a certain area, e.g. the Caribbean, I can quickly turn to a list where all unheard Caribbeans are listed by frequency along with their hours of operation, power along with any other helpful info.
Computer :
These days, especially with laptops/notebooks, many of the lists you need can be maintained on computer. A laptop/notebook is handy for remote DXpeditions though choose one that doesn’t emit huge amounts of radio interference or you’ll curse
the thing!
Misc :
Pens (that work!)
Spare batteries for the recorder.
An aerial switch.
An audio switch (so you can flick between the recorder and the receiver without disconnecting your headphones).
An aerial phaser, tuner, noise-canceller etc.
Power:
If you’re intending to run your receiver off battery, a deep-cycle lead acid battery, similar to a standard car battery in size is strongly recommend. These are very much more powerful than a car battery and able to run heavy loads with little drop in voltage. Some receivers (e.g. Drake R8) run close to 2 amps. Over a week of listening, you’ll need 2 fully charged standard car batteries at
least. A deep-cycle battery also requires different care to a standard battery.
An an auto-charger is recommended for keeping the deep-cycle battery in optimum
storage condition. Typically, these chargers deliver around 4-6 amps initially, then as the charge in the battery builds up and resistance lowers, it flicks into trickle-charge mode to keep the battery in optimum condition. These batteries are 2 – 3 times the price of a regular car battery so deserve that extra care (though worth every penny!).
Now, if you’re running your receiver off mains power, it is possible that noise is entering your receiver via the mains earth. Try running your set on batteries and see if the noise is reduced.
For prolonged operation on DC where battery life is a consideration, the low power-draw of the Drake SPR-4, Palstar R30 and AOR AR7030 and 7030+ are major considerations and all of these sets also provide excellent performance.
Here’s how a typical DX-session unfolds:
Set up the radio, tape recorder etc at least an hour before you would expect distant signals to appear (i.e. up to 2 hours before sunset, depending on propagation).
Make a test recording to verify that the tape/mini-disk is working OK. Check your timer against WWV to ensure it’s accurate and have a spare tape/disk ready to slot into the recorder at a moment’s notice.
Begin tuning with a quick band-scan of the lower SW freqs to get some idea of propagation. In NZ, the first signals to arrive are from the East, rarely
Europe and most likely from the Americas. During Summer (Oct-Feb) from
North America; Winter (May – Aug) from South America and for the rest of the year, either region could be audible first. If signals are readable on the 60 meter band (4.75 – 5.1MHz), it’s time to check for early arrivals on MW. The exact channels to monitor will vary due to your listening location and proximity to NZ-based transmitters, so frequencies quoted below are a guide.
First to be checked are the X-band freqs (1610 – 1700kHz), then the 50kW US channels, 1580, 1520, 1200, 1130, 1120, 1110, 1070, etc, and marker Latin channels like 1470, 1460, 1370, 1230, 1000 etc. Radio Marti 1180 is often the first to fade-in any time of the year and certain channels can produce both North and South America in the first hour or so, e.g. 1560, 1550, 1540, 1500, 1420, 1300, 1290, 1250, 1220, 1190, 1170, 1090, 1060 etc.
You’ll note that many of the channels first checked are above 1MHz. Almost always, the higher MW freqs fire first. Don’t neglect the lower channels though as on the rare occasion, they can be where all the action is. Usually, when they are the early starters, the dominant signals are from the East Coast of the US. Freqs to watch here for North America are 940, 890, 860, 830, 790, 740, 720, 710, 680, 670, 590, 580, 570, 560,
Additionally the following channels favour South America – 980, 970, 730, 620, 610 and deep South America (Chile, Argentina, Uruguay & Brazil) 960, 950, 930, 920, 910, 880, 870, 850, 840, 820, 800, 780, 770, 760, 750, 700, 690, 660, 650, 600, 550 and 540.
On the rare occasion when long-path Europeans are audible, there are several channels, bereft of New Zealanders to monitor. Namely 648, 684, 747, 936, 1107, 1323, 1377, 1422, 1467, 1485 & 1566. These are generally only productive a couple of years either side of the sunspot minima, e.g. 2005 – 2009, and often only heard when sunrise lift at the transmitter coincides with sunset in NZ. The propagation follows the “Greyline” phenomena, virtually travelling in the continuous twilight belt between the two points.
First Signals:
Early tuning involves a helter-skelter approach, flicking between channels looking for signals of substance or something that sounds different to what you’d expect. Note any interesting freqs for subsequent re-checks and make sure that around the top of the hour, you’re sitting on a channel in anticipation of an identification. That’s when a timer that displays seconds is handy, you can arrive on a channel to coincide with the top of the hour identification, not 5 seconds after! Same thing on the half-hour and in the couple of minutes
after network news broadcasts as these are the most common times for local
program content.
The best times for MW signals tends to be from first signal appearance to an hour or two after receiver sunset. This is also before Australian stations start to fade in and provide more interference to deal with.
The Second Wave:
Then in the later evening after local sunset, things start to moderate and can be quite patchy. This is a good time to take a break, have a meal and sit on a channel that shows some promise. That is until stations on the Eastern edge of the America’s approach daylight and can gain strength in a phenomena known as a “Sunrise Lift”. Sunrise lift can last from a couple of minutes to over half an hour as they enter the twilight period. It’s possible for different stations to peak on the same frequency one after the other as sunrise works its way from East to West.
For example on 1180kHz, WHAM Rochester NY can peak, followed by Radio Marti in Florida and then KOFI Kalispell, Montana and lastly KERI Wasco, California. progression of sunrise lifts sweeps westwards until dawn arrives here too though the peaks are more noticeable on East-West paths than North-South. Additionally, stations can sign-on at local sunrise or increase power dramatically as sunrise approaches. Look for stations like KCTA Corpus Christi, Texas 1030 or KATL Miles City, Montana 770 and powerful Latins waking to spring into life.
Well, you have to sleep some time and when on a DXpedition, unless there is a good opening to a particular area other than the Land of Nod, it’s lights out around midnight. If you do stay awake, look for the “midway midnight” phenomena, i.e when midnight is at a half-way point between you and your target. An example, a “midway midnight” opening from NZ to Japan may occur at midnight on a point half-way between the two, e.g. Papua New Guinea, so midnight in PNG, 1400z, could be a good time for a Japan-NZ path to open.
Additional over-night targets are mostly from Asia and latterly the Middle East. A “midway midnight” path into India would be centred on East Timor, i.e. 1500z.
Also, when sunrise hits the West Coast of the USA, pretty much any signal you’ll hear on a 10kHz channel (other than NZ co-channels like 540, 630, 720, 810, 900, 990, 1080, 1170, 1260, 1350, 1440, 1530) will be from Hawaii or Alaska. Many Alaskans and Hawaiians share channels so you may hear either on channels like 620, 650, 670, 720, 750, 850, and 870. Alaskans are seldom heard above 1000kHz whilst Hawaiians are often good on 1040, 1210, 1270, 1460, 1500 and 1540.
Last Chance:
The next phase of listening activity is around an hour before our sunrise. Propagation during this period is from Asia, Europe, Australia, Western Pacific and if you’re very lucky, Africa. Channels to watch are those free from NZers, i.e. 648, 684, 747, 936, 1107, 1323, 1377 1422, 1467, 1485 & 1566, plus 1368 which has a NZer on daytime hours. Most of these channels are dominated by Aussies though target signals may also dominate our Tasman cousins on 657, 711, 760, 774, 1062, 1143, 1179, 1242, 1296, 1359, 1440, 1521, 1548 & 1557. Additionally, there are no Aussies on 909 so if there’s something audible other than the usual NZer, stay tuned!
During this same period, longwave can provide a surprise. Look for Romania 153, France 162, Turkey 180, Germany 177 & 183, Algeria 198, Morocco and Jordan 207 and Russians on almost every channel. During the last sunspot minima (1997), longwave signals were still audible an amazing 2 hours after our sun-rise!
When only NZ signals remain on the dial, it’s time to take a break, catch up on some sleep, prepare for the next assault on the air-waves and dream of QSLs.
