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Early Radio, prior to World War 1 focussed on long and medium wave transmissions. These cover from approximately 10kHz to 1600kHz. Broadcast long wave transmissions cover from approximately 150 to 300kHz and medium wave broadcast from about 500kHz to 1600kHz. Transmissions on these frequencies are carried principally by a “ground wave” during the day and by a “sky wave “ toward evening and at night time, where the signal can cover greater distances because it is reflected from the ionosphere.
Radio Amateurs (“Hams”) are credited with the discovery of shortwave radio and the opening up of frequencies from 1600kHz to 30 MHz. Above 30MHz, is considered to be “Ultra Short Wave” or “Very High Frequency” (VHF). Using simple radio equipment, amateurs were able to establish transatlantic contact on a frequency of 2.72MHz in 1923. Success bred success and the shortwave bands became commercialised. Inevitably, the shortwaves had to be regulated and portions were set aside for broadcast, amateur radio, commercial and military use.
The way in which a radio wave is sent from a transmitting antenna (aerial) to the receiver is referred to as propagation. Shortwave radio waves are propagated by reflection from ionized layers in the Earth's atmosphere. These layers receive charged particles from the Sun, which are trapped by the Earth's magnetic field. Different shortwave frequencies are reflected by different layers, which is why you will hear broadcast stations, such as the BBC on 21.470MHz during the day, and on 3.255MHz during the night. The radio wave can be reflected many times between the transmitter and receiver. This allows transmitters of fairly modest power to be received over great distances. Occasionally, the signal will be received over a short path, and over a long path, having “gone around the world”. The transmissions arrive at slightly different times and give rise to a peculiar flutter.
The Broadcast Bands
Most people will probably be interested in receiving radio broadcasts on shortwave. Before the Internet, shortwave broadcasting was the only way to get an alternative point of view to that put out by the media of any particular country.
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No Self Respecting Radio of the 30s and 40s would be without shortwave |
Some countries ban the sale of shortwave radios (in South Africa, general coverage radios able to receive above 30MHz are illegal to use and possibly to own. This covers sets like the iCOM PCR-1000 and air band radios.), but in most countries very inexpensive shortwave radios are available. Most early radios have shortwave and make excellent broadcast receivers. From the beginning of World War 2 (perhaps earlier) until the end of the cold war, radio was used as a means of propaganda by both sides. In Britain, I used to hear Radio Moscow over the ineffective jamming by the US and also Voice of America over the ineffective jamming by the Soviet Union. More recently, we could enjoy Radio Zimbabwe and Shortwave Radio Africa carrying on the same tradition. Note that countries can “cut off” the Internet to censor news, but have to resort to jamming unwanted shortwave broadcasts.
The broadcast bands are organised portions of the radio spectrum. Normally referred to in terms of wavelength. You can convert wavelength in metres to frequency in MHz using the relation frequency = 300 / wavelength. Or wavelength = 300 / frequency. Thus 1MHz = 300 Metres, 30MHz = 10 metres etc.
The following table has been reproduced from Wikipedia:- (I will deal with “DRM” shortly).
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Metre Band
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Frequency Range
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Remarks
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120 m
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2300 - 2495 kHz
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tropic band
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90 m
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3200 - 3400 kHz
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tropic band
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75 m
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3900 - 4000 kHz
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shared with the North American amateur radio 80m band
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60 m
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4750 - 5060 kHz
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tropic band
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49 m
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5900 - 6200 kHz
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41 m
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7200 - 7450 kHz
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shared with the amateur radio 40m band
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31 m
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9400 - 9900 kHz
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Currently most heavily used band
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25 m
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11,600 - 12,100 kHz
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22 m
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13,570 - 13,870 kHz
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substantially used only in Eurasia
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19 m
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15,100 - 15,800 kHz
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16 m
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17,480 - 17,900 kHz
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15 m
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18,900 - 19,020 kHz
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almost unused, could become a DRM band
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13 m
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21,450 - 21,850 kHz
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11 m
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25,600 - 26,100 kHz
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may be used for local DRM broadcasting
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The Amateur Radio Bands
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Metre Band
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Frequency Range
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Remarks
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2200 m(?)
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135.7 – 137.8 kHz
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Long Wave
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160 m
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1810 - 1850 kHz
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Top Band
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80 m
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3500 - 3800 kHz
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Music Transmissions Permitted
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40 m
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7000 - 7200 kHz
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Recently Extended
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30 m
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10100 - 10150 kHz
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Phone permitted during daylight hours in S Africa.
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20 m
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14000 - 14350 kHz
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Popular DX Band. Listen on 14195kHz
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17 m
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18068 - 18168 kHz |
WARC - added 1979 |
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15 m
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21000 - 21450 kHz
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Also good for DX. Listen on 21260 kHz
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12 m
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24.890 - 24990 kHz
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10 m
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28000 - 30000 kHz
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7 m *
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40.675 – 40.685 kHz
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Technically, a VHF Band., as it is above 30MHz
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6 m *
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50000 – 54000 kHz
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Music Transmissions Permitted. Also a VHF Band
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* Some shortwave radios cover these bands (e.g. National NC 109, iCOM R-75)
There have been some recent additions to the amateur bands –If you are interested in becoming a radio amateur, I urge you to look at SARL's pages and consider joining. Thanks to John Green ZS1GHG for additional information on the Amateur Radio Bands.
Types of Radio Transmission
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Amplitude Modulation
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AM
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Most common form of transmission used by broadcasters. Requires simplest radio receiving equipment.
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Digital Radio Mondiale
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DRM
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Arguably the next most common type of broadcast transmission. I don't think you will receive DRM transmissions in South Africa yet, and there are still not many receivers around. You can make your own DRM receiver using a PC sound card and prodigious programming skill. DRM provides nearly FM quality on the shortwave bands.
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Frequency Modulation
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FM
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Not used much on shortwave – if at all. Possibly by amateurs on the 10 metre band.
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Single Sideband
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SSB
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Only broadcaster I know is AFN on 4319kHz (USB). Still used a great deal by radio amateurs. A form of AM in which the carrier and one sideband is suppressed. Bands above 40m use upper sideband (USB), bands 40m and below generally use lower sideband (LSB).
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Double sideband/Independent Sideband
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DSB, ISB
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Used by commercial stations and telephony. (You probably shouldn't listen to these transmissions!)
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Radio Teletype
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RTTY
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Used by radio amateurs. You can download a program such as MMTTY to resolve RTTY transmissions.
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Continuous Wave (Morse Code)
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CW
MCW
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Used by radio amateurs. Although there are computer programs that turn Morse Code into text – it might be a satisfying challenge to master it! (MCW is “Modulated Carrier Wave” - Not used any more.
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Slow Scan TV
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SSTV
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There are programs available that will let you decode this. Listen on 14230kHz
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Fax, Weather Fax
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These are fax transmissions of weather maps and other strange things. The Wefax program will let you decode weather satellite transmissions. (This is probably illegal in South Africa.)
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Other digital transmissions
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There must be hundreds of these. You can download decoders for many of them.
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Jammers, Bubble Jammers
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Used by governments to hide information for the benefit of their citizens.
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Shortwave Radio Receivers
In addition to the tuning and volume controls of domestic radios, shortwave radios may have other controls:
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BFO
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“Beat Frequency Oscillator” Used to resolve CW transmissions. May also be used to resolve SSB in receivers designed for AM.
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RF Gain/”Anti Cross Modulation”
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Used to lower the gain of the RF stage (if there is one). Can prevent overloading of the receiver by Strong signals. May improve reception of a weaker signal in close proximity to a strong station.
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IF Gain
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Lowers the gain of a receiver to prevent overloading of a receiver by strong signals.
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RF Attenuator
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Performs a similar function to RF gain control
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Noise Limiter/Blanker
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Used to reduce impulse noise from atmospherics, motor vehicle ignition systems etc. Might have a control to adjust limiting level
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AGC On/Off/Slow/Fast
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Controls the automatic gain control circuitry of the receiver. You might need to adjust this if the received station has rapid fading. Slow AGC is preferred for SSB, and Fast for AM. (At least one commercial radio has this the wrong way round!)
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Bandwidth/ Selectivity
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AM transmissions need a wider bandwidth than SSB, which in turn need a wider bandwidth than CW. The minimum bandwidth for AM is about 6kHz. Some radios adjust this automatically (e.g. Barlow Wadley, Kenwood R1000)
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Synchro/Sync
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For synchronous demodulation of AM signals. On shortwave AM signals become distorted as different sidebands fade selectively. The synchronous demodulator may improve the fidelity.
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Notch Filter
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Adjacent stations may produce an annoying 5kHz “whistle”. The notch filter can remove this. Normally you can control the notch depth as well as frequency.
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Crystal Phasing
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In sets with a single crystal filter, there may be a notch (see above) which you can use to tune out interfering stations
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Crystal calibrator
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Used to produce accurate “pips” so that the radio tuning scale can be accurately calibrated.
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Squelch/ Muting
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Used to silence a receiver until a signal of a predetermined level is received.
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Passband Offset
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You can use this to vary the IF frequency slightly in order to change the quality of SSB reception without changing the frequency.
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DSP
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Digital signal processor – This is used to process the received signal digitally. Commonly will provide an automatic notch filter and a filter to enhance the signal to noise ratio of weak signals. (Can be quite stunning!). Some radios process the entire IF digitally.
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Scan Controls
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Modern radios can automatically scan for stations and have a remarkable set of “programming” options.
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Memory controls
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Stations (and their names) can be stored in pre-set memory locations and recalled for later use.
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Megacycle Change
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Radios like the R390 and the Barlow-Wadley have 30 or so wavebands, each spanning 1 MHz.
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Kilocycle Change
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For tuning within each waveband
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Audio Filter
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Produces extremely narrow audio response. My EC10 and R390 had this – but I don't really “get it”.
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Stand By
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For use with a radio transmitter. Changes over from receive to transmit and mutes (desensitizes) the receiver.
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Mode AM/FM/CW/RTTY
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Switches between different receiving modes. (The FM switch doesn't switch the set to broadcast FM necessarily! - often switches to narrow band FM.)
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Antenna trimmer
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Supposed to match the receiver input stage to the antenna. Sometimes a BIG capacitor is used so that complicated tracking of the first RF is avoided.
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The above list is not exhaustive. Most shortwave radios will also have some sort of tuning indicator. This could be a “Magic Eye”, a mechanical 'S' meter or perhaps a bar chart on an LCD display. The cheapest shortwave radios may just have an LED. Some radios have a “bandscope”, which displays a bar chart of what's going on in the vicinity of the received station.
Shortwave radios vary in price from about R45-00, say $7 (don't laugh)
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A very inexpensive set! |
to hundreds of thousands for sets that are probably illegal to own. As might be expected, the R45-00 set is hardly a star performer, but it will receive the BBC. It also works very well on the FM broadcast band. I think the claim of “150 Watts peak music power out” could be an exaggeration, as it works from a couple of torch batteries.
Unless you live on an isolated farm, I wouldn't be particularly keen to rush out and purchase an expensive table-top shortwave radio. There are quite a number of portable radios to choose from, including the Sangean, Grundig (Eton), Kaito and Sony receivers. These are in the price range R400-0 to R4000-00. If you are a radio amateur, or have a friend who is one, you can consider erecting aerials that will combat the various forms of interference, then a table-top radio might be your preference. Second-hand radios are also worth looking out for – but remember that sets made in the last 20 years are very complicated, so be extra extra careful to ensure everything is working the way it should and that no modifications have been made.
Here are some factors to consider when choosing a shortwave radio:-
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Factor
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Remarks
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Price
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Remember the law of diminishing returns. Spending twice as much doesn't mean you'll get a radio twice as good. If you are spending more than about R4000-00 – take a look at a few more articles than this one.
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Appearance
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Most shortwave radios are ugly. Some of the portable radios aren't too bad and at least can be hidden in a drawer.
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Portability
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Portable sets can be taken to places where there is no PLT. You don't have a long aerial that takes lightning into the set. They're light in weight and don't consume much electricity. You can take them on holiday with you.
On the other hand, they can be stolen more easily. They can fall and break. They may lack one or two features of a table top set. You can lose them (really).
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Sensitivity
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This is measured in microvolts for a 10db signal to noise ratio. Bearing in mind the amount of external noise, somewhere around 1 microvolt on AM should suffice. Too much sensitivity might indicate the set is susceptible to overloading.
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Stability
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Modern digital display radios use a frequency synthesizer. There is a Kaito set that looks like an analogue radio, but uses a PLL synthesizer. High stability is needed for SSB reception, because you don't want the set to drift off the station. If your main interest is broadcast AM, then you shouldn't have a problem.
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Tuning and backlash
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When you tune a radio set, you want the station to be at the same point on the dial every time. You don't want to turn the tuning knob overshoot and then have a bit of slack before the tuning drive begins to work again. The very cheap radios are simply awful in this respect and even the more expensive sets may not be satisfactory. Tuning knobs should spin freely, evenly and smoothly. Note that analogue radios tune continuously, whereas most sets in this price range tune in discreet intervals of 1kHz, with the option of 100Hz for SSB. Be careful if you're buying second-hand.
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Tuning knob or buttons ?
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I am used to buttons now. Some of the tuning knobs on the digital sets are sort of annoying. Try before you buy.
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Selectivity
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Some sets have a maximum bandwidth of 6kHz on AM. Unless you are buying the set purely for DX – this isn't enough. Also the shape of the selectivity curve is important. For me, the R390A receiver gets everything right, with its choice of bandwidth from 100Hz to 16kHz and steep sided, flat topped selectivity curves.
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Strong signal handling
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I am sorry to say that receivers in the price range R400 to R 4000 are probably going to fall short in this department. Perhaps its not as important in South Africa as it is elsewhere, where there may be strong radio transmitters on every street corner … almost. If you are a keen listener and live in close proximity to a radio transmitter, you might have to investigate receivers that can cope with the problem.
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Audio quality
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You should check this out. Listening to a radio with poor audio for any length of time will get on your nerves.
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Operational modes
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Do you need them all? If your principal interest is listening to shortwave religious broadcasts, then all those SSB etc. reception modes are not a necessity.
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Frequency coverage
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Do you need broadcast bands only, amateur bands only or full coverage? Take care to look at the band coverage - the Sangean ProTravel PT-10, for example, does not cover the tropic bands. I haven't checked the equivalent radios from Sony and Panasonic.
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Image rejection
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This is important because images can interfere with the wanted station.
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Spurious responses - Spurs
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These are unwanted signals generated within the receiver. Usually, you will get this problem with complicated receivers. The Barlow-Wadley suffers from spurs at each end of the kHz scale. “Use them to calibrate your receiver” the manual advises. Very often, they are quickly tuned through and don't matter.
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Battery Life
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Changing batteries often is a nuisance and might be expensive. If buying a portable, check this out. If the set requires “D” size batteries – don't be a cheapskate – get the real deal 10 Amp Hour NiMH rechargeables, or 5 Amp Hour NiCad. The NiCads have lower self discharge and may actually last longer between charges.
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Features
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Memory, Bandscopes, Digital modes … the sky's the limit. Beware of sets that use one button or knob to control 6 or 7 things, because you'll never remember how to operate the thing, unless you're a teenager. Note to teenagers - one day you will have trouble remembering things 
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New or Pre-Owned
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Sets manufactured from the mid '80s to the present can be very difficult to repair if something goes wrong. Make sure your new radio is guaranteed and that you can get it serviced easily.
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What about home-made?
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If you succeed – its a great feeling and you will learn a great deal. There's a plan for a home-made set here. - all the parts are available locally Cost should be less than R200-00 including valves.
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Aerials for Shortwave Radios
The requirements for shortwave listening are different from those of radio amateurs. Although there is a “law of reciprocity” that more or less states that an aerial that is good for transmitting will also work well for receiving, transmitting aerials are duty bound to take all the power from a transmitter and radiate it without sending anything back to the transmitter. The reflected power would be lost, or worse, may damage the transmitter output stage.
Having said that, if you want to, you can consult books such as the ARRL antenna handbook and use high efficiency antennas, such as beams and log-periodic, but a) it might annoy your neighbours and b) be sure you have a receiver that can handle both strong and weak signals.
For most purposes, a “long wire” aerial (say 20 metres long) will suffice. Try and string it as high as possible and arrange the downlead in a shielded cable to reduce interference. An alternative might be to use a dipole aerial.
What you will find is that these simple aerials perform better on some bands than others and that they may prefer to receive from certain directions, but they will work well enough for general use.
Many shortwave radios come with a built-in telescopic antenna. They have very sensitive RF stages and simply work best on the antenna supplied. If you attempt to use an external antenna, these sets simply overload and all you will hear is loud sharsh or noise. Some sets have the option of attaching an external “active aerial”. I haven't tried this, but it sounds like a great weekend project. (Even the great R390 was designed to work with a short whip antenna.)
The Decline of Shortwave
Sales of shortwave radios always decline during times of sunspot minima. This is because reception is impaired. For a long time now, we have been in a long sunspot minimum. The sun normally has periods of high and low sunspot activity in cycles lasting about 11 years. The most recent sunspot maximum has been poor, with little sunspot activity, making shortwave radio more challenging. News as of this week (Feb 15, 2011) is that solar activity has shown some increase, starting with a CME (Coronal Mass Ejection). Solar flux is reported to have risen by 50%. Look here and here for information on propagation.
Modern lifestyles, in which high stress levels and competitiveness abound also contribute to the decline. Many people are too exhausted to do anything other than be entertained when they arrive home after work. Television, rather than shortwave radio is the medium best suited to letting the average consumer unwind.
Without a doubt, computers and the Internet have also contributed to the decline. An internet radio can receive 25000 or more stations (what – you're going to rush out and buy one?) without fading or any other of shortwave's failings. If you have a home computer connected to the Internet, then you can download programs such as “Radiosure” or “Phonostar” and get an internet radio for free. Added to which, you can choose by genre, country, and so on. You can even listen to airport control towers without fear of prosecution.
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An Internet Radio |
Broadcasters are now diverting funds away from shortwave and channelling them into Internet radio, satellite (DSTV) and so on. (Satellite radio per se was not a success in South Africa – only WRN still transmit on Worldspace frequencies).
Finally, most developed countries have decided to adopt something called “PLT” (Power Line Transmission) or “BPL” (Broadband over Power Line). This is digital transmission over electrical power lines. Now, it won't have escaped your notice that power lines look like extremely long wire antennas. Since digital transmission involves the very rapid switching of signals on and off, the result is that these antennas transmit extremely high levels of noise. In my own case, this noise exceeds S9 on many of the lower frequency bands, making them useless for DX (long distance) reception.
Other sources of noise are ADSL signals on telephone lines – again a real nuisance, but perhaps more forgiveable than PLT.
Perhaps we should support organisations like the SARL that promote the use of shortwave and fight the continued use of PLT. Hmm perhaps I should join. |