3: MW Receivers
The second most important piece of equipment that DXer needs is a receiver. Second? Yes, because without an aerial even the best receiver is no use at all.
Over the years receiver technology has evolved but a MW receiver made in the 1930s will still work alongside one made today because the fundamental signals being broadcast haven’t changed much in that time.
There are hundreds of receivers to choose from and many DXers have more than one for different reasons. This isn’t the place to discuss individual receivers but they do fall into six major camps with their various pros & cons.
Receiver classes (pre-2000)
Some listeners like the retro feel of using a refurbished old/classic radio. Mostly these will be valve based of pre-1970s vintage. Ironically many DXers active today started their listening hobby using radios like these. Some models were surprisingly good receivers.
This describes a radio so heavy that it could be used to moor a boat. Most are ex-military and range from pre-WW2 through to the 1980s. Many are good performers on MW, but a few are notoriously bad. They tend to be power hungry and need maintenance from skilled hands and sometimes hard to find parts. Perhaps exemplified by the most expensive mass produced radio ever made, the Collins R390A/URR, epitomised by its amazing engineering and performance.
Large sophisticated radios, initially with valves then later semiconductors. Most are for desk top use (some are rack based) and many bear similarities to amateur radio transceivers. Many emerged from Japan (from companies like Icom, Yaesu, Kenwood, JRC) and most DXers aspired to own one of these in the 1980s/90s. But sometimes an old second hand boat anchor would be cheaper and give better performance. Developments in the mid-1990s led to one of best receivers of its class in terms of RF specification and audio quality, namely the AOR AR7030+. This took the communication receiver and turned it into a sophisticated desktop receiver.
This is a radio easily carried in one hand; The first generation was in fact the battery-powered miniature valve based radios of the 1950s-60s, but these were soon displaced by the Japanese mass production of the pocket transistor radio. By the 1980s portable radios appeared with digital frequency tuning but most offer little to the DXer. One or two exceptions appeared, most notable the Sony ICF2001D with its celebrated synchronous AM reception and good DX reception performance. Popular brands included Grundig, Sangean and Sony.
Technically these are just portable radios but an entirely new generation emerged around 2006 and bore no relation to traditional radios that went before. They look similar to digitally tuned radios of the 1990s but internally there is no similarity.
Nearly every portable (and most other receivers) previously was based on the super-heterodyne design principle. But the new generation used digital signal processing to build a radio that was almost all on one silicon chip. It dispensed with conventional issues like receiver tuning alignment and a large component count. Therefore they were cheap – but definitely not to be ignored. Ultralights are manufactured to use a small internal ferrite rod aerial but many enthusiasts have found ways to boost antenna effectiveness and make these cheap little radio very effective DX tools. Nearly all ultralights have come out of China but some appear to be “closely inspired” by American precursors.
Software Defined Radio (SDR).
This a fundamentally different approach to receiver design. The receiver is basically just an extremely powerful analogue to digital convertor that captures large chunks of radio spectrum at once and digitises it. Once digitised it can be processed in real time or stored in computer memory for post processing. This digitising process is directly analogous to converting analogue music to digital music stored on a CD or shared as an mp3 file.
Digital processing performs all the functions normally expected in a radio, tuning, selectivity, demodulation, automatic gain control and much more. One can almost think of an SDR as a dongle attached to a computer – and indeed a few are just that! The quality of the A-D and associated circuit design is important but the software and the user interface is even more so. Modern SDRs can be connected to GPS clocks for extreme frequency stability and ultra-precise tuning. They can be connected to databases to identify signals. Perhaps most significantly they liberate the DXer from using their radio to listen to just one frequency at a time. The benchmark SDR for the MW DXer was the Perseus which was the first radio that could record the whole MW band continuously. That meant the DXer would not miss any signal that was audible – provided they had enough time to listen back to the recordings (actually a human impossibility!). To make the most of an SDR the DXer needs to combine signal intelligence with traditional DXing skills.
Some people describe the difference between using an SDR and a traditional single channel receiver as similar to the difference between fishing with a rod & line and using a trawler. The other big difference is that DXing with an SDR and a computer display allows the DXer to employ two senses, rather than just one, in the search for interesting signals.
As you can see from the screenshot above lots of important information is displayed visually rather than just audibly. Often it possible to get a good idea of which stations are visible before they are audible.
Books have been written on the topic of receiver design & performance. Usually, but not always, better performance increases the price. A DXer deserves the best receiver possible!
Sensitivity – or the ability to hear a weak signal. This is rarely an issue for MW receivers unless the receiver has been deliberately desensitised on the MW band to prevent overload by strong signals. In some situations such as remote locations or DX-peditions sensitivity can be an important requirement.
Selectivity – or the ability to separate the desired signal from others on nearby frequencies. The MW DXer will find stations separated by as little as 1kHz so a receiver that has good selectivity is important. Selectivity can be enhanced by a receiver with good single sideband reception or synchronous AM detection. Modern software defined radios have exceptionally good selectivity that can be fine tuned to reception conditions. In contrast good selectivity in older analogue receivers required expensive components and excellent design and construction.
Ease of tuning; the original MW radio just had one knob to tune the radio slowly up and down the dial from 520-1600kHz. That is obviously slow and not very accurate for finding a precise frequency. The introduction of digital display of the frequency that the receiver is tuned to was a game changer for the listener. The ability to enter a frequency from a keypad also made tuning and jumping quickly between frequencies easy. The logical next development was to give the radio memories to store popular frequencies. Digital control of analogue receivers emerged in consumer grade receivers around 1980 and this was a huge step forward for DXers.
Drift – or frequency stability. Old radios had very poor stability compared with modern receivers and this affected valve based receivers as much as modern transistorised radios. Big improvements in stability appeared in receivers using frequency synthesis for their tuning from the 1980s. But even that was not sufficient for some applications – today many hard-core MW DXers lock their receivers to GPS frequency standards to get the ultimate accuracy and stability.
Other important factors are whether an external antenna can be connected and whether the receiver can feed audio to headphones or to a recorder. Sometimes a receiver that can work off batteries rather than mains power is an important requirement.
Once you get immersed in the hobby I’m sure you won’t be able to resist the temptation to accumulate various receivers.