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Above - The excellent Sony and Roberts radios are neat portables suitable for Short Wave listening and a spot of MW, LW and VHF DX-ing too. Both models offer many facilities and very good reception.
Some recent classics:
So now you have your radio - What is DX-ing and why? DX-ing is the long distance reception of a distant radio station or transmitter that is not usually intended for reception at your own locality. Despite the advent of DAB digital radio and radio delivered by satellite there is is still much fun to be had with long distance reception ("DX-ing") of long-wave, medium-wave and short-wave radio stations and even v.h.f/FM too. DAB certainly gives a good choice of some of the mainstream stations but, in the main, listeners can only receive what the authorities intend us to hear. A DAB multiplex uses a Single Frequency Network to carry the signals to the listener. The single frequencies are used and re-used all over the country to obtain a wide coverage, unlike traditional AM and FM broadcasting which must use a different frequency for each area or region to avoid interference. The Single Frequency Network of DAB provides rubust reception, but does not generally allow DX-ing since the frequency of the local multiplex may be the same as the multiplex that you wish to hear 50 or 100 kms away and so is effectively blocked. With analogue AM or FM if you are bored of your local radio station chances are that you can tune into an alternative distant radio station (given a suitable aerial) since it is likely to be on a completely different frequency to your own local station, this is often not so with DAB. For Fun Chances are that if you live in the Midlands you could tune into local stations in Manchester or London or other areas. This can sometimes be because you want to hear the programme material being broadcast on a different distant station and often because it is just great fun to pluck a weak and interesting station out of the ether.
What do you need for long distance reception - DX-ing? Medium Wave & Long Wave DX-ing: Nothing too special is initially required, though as you become absorbed into the hobby bigger aerials and a better radio may be desired, but to start off with just a reasonable quality portable radio from a good radio name such as Roberts, Sony Grundig, Sangean or Panasonic may be all that is required to pick up very distant medium wave and long wave radio stations. A decent portable mw/lw/fm radio will cost about £30-£40 and will allow long distance reception especially on medium wave. You will also require an aerial suitable for distant reception, the best, easiest and smallest being a LOOP AERIAL. See the page Loop Aerials and ATU's for details on how to make a simple Loop Aerial that will allow some good DX-ing even with a modest portable radio. Eventually as listeners become more involved in the DX hobby a better communications receiver may be desired, such as a Palstar R30 or AOR AR7030. A long wire aerial can be employed, strung around a loft or down a garden to grab those really weak and far-flung stations, and a bigger and better directional loop aerial could be made. Again see the LOOP AERIALS and ATUs pages. VHF / FM DX-ing:
If
you also want to get into VHF/FM (Band 2) DX-ing from 87.5 MHz to 108
MHz then it is handy if the radio you use has an external aerial socket
so you can connect an external DIPOLE AERIAL or YAGI that can be
positioned in a loft or preferably outside. Even better will be
to
obtain a 4 or 5 element VHF Yagi aerial mouted on a rotator outside so
that it can be electrically moved and pointed into any desired
direction. During good reception conditions such as 'Tropospheric
Lift or Ducting' and 'Sporadic E' that occur periodically during the
year reception of stations at unimaginable distances can be
experienced.
An external aerial can often be plugged into a portable radio that is fitted with a suitable socket and can offer surprisingly good results. A hi-fi system that includes a good quality VHF / FM tuner can be used to obtain some great 'DX' during the good 'lift' conditions when connected to a quality external aerial. It is important that the tuner has quite narrow IF filters to separate out the croweded stations, and some tuners offer different IF filter settings, so when DXing always choose the narrowest one. Check in the instruction book. The quality of tuners is quite variable, the 'separates' hi-fi tuners are usually very good, whereas the tuners that are built into a mini or midi stereo system or 'music centre' can often be quite poor, being noisy, insensitive and having wide IF filters that give poor selectivity - some are surprisingly good, however, so it's always worth a try. During periods of good reception it is often possible to hear transmitters and local radio stations from hundreds of miles away and even European stations can be received at such high strength that the RDS (Radio Data System) information is decoded and displayed on those tuners that have the RDS facility.  A high quality Sony STSA50ES Tuner Other VHF and UHF
frequencies:
A scanner, such as the one seen in the picture of the 'listening post' above, will provide reception of frequencies above the Short Wave bands right through the VHF (Band 2) broadcasting bands and beyond - right up to UHF (Ultra High Frequencies). The actual frequencies that a scanners will cover depends upon the model, but frequencies from approximately 25 MHz (the top of the short waves) to 1300 MHz are typical. Some scanners offer this in one continuous band, but others omit certain small ranges - so check that the scanner you intend to obtain includes the frequencies that you wish to monitor! This wide range of frequencies can enable monitoring of Amateur Radio Operators and other utility services using Narrow Band FM (n.b.f.m.) and sometimes narrow AM modes of transmission. The newer encrypted digital modes of transmission will not be heard as anything other than a 'mush', it must be noted. The scanner can continually monitor a set range of frequencies - scanning through the range every few seconds. Alternatively a hundred, and usually many more memories are provided to memorise the favourite or most frequently used frequencies. The scanner can then be set to scan all or some of these memories only stopping on a memory channel when the frequency is active and a signal received. A scanner requires a specialist aerial that can cover the enormous range of frequencies - a DISCONE is the most popular choice and is arguably the most effective, although there are alternative aerials available - both passive and active. Some of the alternatives look like white plasic sticks and these have the aerial elements inside, some include an active remeotely powered wideband RF amplifier - these are known as Active Aerials. Active aerials work well when the listener is away from a town or main conurbation, but can be easily overloaded if situated near to an active transmitter of which there will be many in a town or city. It is often best, therefore, to use a passive type unless signal strengths are particularly weak in the area where the scanner is located. SHORT WAVES:
Short Wave Reception - And more about the radios Tuning to ShortWave can reveal many stations from all around the globe. Many of the stations heard will be from International broadcasters wishing to make their own country's views heard the world over. Additionally Amateur Radio operators can be heard chatting on the short wave bands, which can often prove very enlightening, especially if you are after some technical tips.  AOR AR7030 The short waves range from 3000 kHz to 30,000 kHz are used since they are reflected off a layer in the earth's atmosphere known as the Ionosphere. The ionosphere lies at a height of between 50 and 400 miles above the surface of the earth. This means that signals that may have otherwise been lost as they travelled straight out into space are reflected by the ionosphere back down to earth many hundreds, if not thousands of miles away from the transmitter site for distant audiences to tune into. Sometimes high frequency radio signals can be bounced several times through the ionosphere before returning to earth, or even bounced back off the surface of the earth and again off the ionosphere to enable reception on the opposite side of the globe. There are portions of the short wave band that are reserved for broadcasting and these are usually referred to as the short wave bands. eg 49meter band (6MHz) , 41meter band (7MHz) and 31meter band (9MHz). See "THE BANDS" table below. Some of more inexpensive 'dial and pointer' analogue radios tend to separate these into distinct switchable ranges, missing out the wavelengths in between. Digitally tuned radios may cover everything from 4MHz to 26MHz continuously without switching, many cover everything from 1.6 MHz right up to the top of the band at 30 MHz without missing out any frequencies. Not all of the short wave band is used for 'broadcasting' programmes. There are many frequencies in between these broadcast bands that have, in the past, been used for 'Utility' stations which carried Morse Code, FAX, RTTY (Radio Teletype) from newsagencies and other modes of transmission such as AMTOR. These all make strange beeping noises but can be decoded with special hardware decoders or by using software on a PC. Have a look in Short Wave Magazine for more details. Much of this utility traffic has gone now, replaced by internet, computer and satellite. However there is still much voice traffic. Much of the voice traffic will be from military sources - army, RAF, USAF and Navy - and from commercial aircraft and shipping and from coastguard and rescue services. If you refer again to THE BANDS table below you will see that Amateur Radio operators have specifically designated band on which they are allowed to operate, these bands are often buzzing with conversation. Remember that in general most of these voice transmissions will be in Single Sideband mode (SSB). And as a rule of thumb the frequencies below 10MHz (10,000KHz) use Lower Sideband, while the frequencies above 10 MHz use Upper Sideband (USB). You may sometimes have to listen for a while before hearing anything as not all the frequencies are active all the time. Have a look at the SOME INTERESTING FREQUENCIES notes at the bottom of this page for some ideas of where to tune into. Why do some frequencies appear to be completely dead? As a very rough guide, and from my own experience, frequencies between 12MHz to 30MHz work better during daylight hours, due to the way the ionosphere propagates the radio waves. During the night they will usually seem very quiet or completely dead - especially as the broadcasters, knowing that propagation at this time will be very poor they will switch their transmitters to other frequencies. At night time frequencies below 12MHz tend to be propagated more effectively by the earth's ionosphere, so broadcasters will use these more extensively during darkness and they will usually appear to be very active at night. The 49 meter band (6MHz) and the 41 meter band (7MHz) are usually the best, though the 75 meter band (4MHz) and 31 meter band (9MHz) are often good night time choices too. More about radios: To obtain the short wave bands a slightly more expensive radio than the average mw/lw/fm portable will be rquired. Some inexpensive portable analogue (dial and pointer) radios offer one additional short wave band, usually the 49 meter band, that will enable reception of many of the main international broadcasts from around the globe on a simple telescopic aerial and this can be a good introduction to the world of short wave. For the more ambitious a dedicated shortwave / worldband portable, such as those pictured at the top of this page will be more desirable, and indeed necessary if you wish to tune into the SSB transmissions. So, moving up the radio market a little there is a good choice of digitally tuned portables that offer very accurate tuning and much wider and continuous coverage of the short wave bands. Again a radio from a good manufacturer will be needed for satisfactory results, as the very cheap radios that are often labelled 'world band' that can be seen on offer in discount stores or your local market will prove very unsatisfactory as they are poorly designed being very unselective meaning that they cannot adequately separate one station from another on the crowded short wave bands. These cheap radios can be had for as little as £20 but will also prove to have very inaccurate tuning dials, so you just won't know to what frequency you are tuned. They are often insensitive which will mean that the weaker stations will not be heard and always suffer from a poor image rejection ratio which manifests itself as stations appearing not only at the intended position on the dial but also at several other positions causing much unwanted interference and noise. The best bet for an introduction to good short wave reception is to buy a portable radio manufactured especially for the purpose which uses a digital readout for accurate tuning so you always know to which frequency the set is tuned along with continuous coverage of short wave. Popular manufacturers for such sets are Sony (eg ICF-SW35 or ICF-SW7600), Roberts (eg R9921, R881 or R861), Grundig (eg YB400 or Satellite 800) and Sangean (eg ATS 404 and ATS 909). See O'Gormans Radio for some examples. The higher specification, and therefore more expensive, communication receivers that are dedicated to mw/lw and sw are produced by Palstar (i.e. R30), AOR (i.e. AR7030), ICOM, KENWOOD and YAESU (FRG-100) amongst others.  Vintage Grundig Satellit multiband radio |
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AERIALS: No matter how good your radio it must
be fed by a good antenna!!
For Medium Wave and Long Wave
The
most effective aerial for mediumwave and longwave DX-ing is probably a loop aerial. A loop aerial is useful
because it is often easier to use than having to string up a large
long-wire outdoor aerial. A loop aerial is very discriminatory in
that it is both Directional
and Selective. The
directionality
can help null out unwanted interfering stations and the selectivity
prevents overloading of the radio because the loop is tuned into the
frequency of the desired station, rejecting all others. A long
wire aerial can easily overload the tuning circuits of a radio and the
directional and selective characteristics of a loop avoid this.
When I constructed my first medium wave loop aerial I was utterly amazed at its performance - pulling in stations that I had never heard previously. I still think, even considering its simplicity, that the loop aerial is best piece of equipment I have ever made! Traditionally such an aerial is wound around a large wooden frame often 100cm x 100cm and connected directly to a receiver using the external aerial socket. A typical example is seen in the centre photograph above. For portability and for effective use with a portable radio a smaller loop can be constructed so that a typical portable radio can sit in comforably in the centre and the signals received by the loop aerial coupled to the radio's internal ferrite rod aerial. |
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An Aerial For Short
Wave Random Wire Aerial [Click on the picture to see some more ideas about aerials on the Lowe HF-150 page!] To
obtain good short wave reception it is absolutely essential to have a
large enough aerial placed as high as is practical and positioned as
far
away from any sources of electrical interference as possible.
The easiest and therefore most common aerial for shortwave reception is simply a length of wire suspended as high as possible and as far as possible, often referred to as a 'long wire', it is more correctly termed a 'Random Wire' since its length is not cut to be resonant with any particular wavelength. A random wire may be 10 to 30 meters long and be strung around the loft or down a garden slung from poles or trees, or even around all four walls of the listening room. (This long random wire aerial can also be used for medium and long wave reception - though I still prefer to use a loop aerial for these bands.)
If a communications receiver is being used then the long random wire aerial can often be connected directly to the set's antenna terminals, as many receivers of this type can handle the strong signals present. Even better is the use of an ATU (Antenna Tuning Unit) as this will help with better signal transfer: ATU's (Antenna Tuning Units) Connecting a long aerial directly to the telescopic aerial of a portable radio, in particular, can cause serious overloading of the radio's 'front end' (the tuning circuits) producing lots of unwanted noise and interference.
However should reception conditions be very good and signal strengths are very high then too much signal could swamp the radio's tuning circuits. In this case an attenuator will be very useful, giving the ability to gradually reduce the incoming signal. A simple attenuator consists of a variable 1k resistor which can be incorporated into the ATU circuit. For more information on LOOPS, AERIALS and ATU's and some useful circuits have a look at the LOOP AERIALS and ATUs page. THE BANDS: Short Wave:
Domestic Broadcasting:
SIGNAL METER CALIBRATION: Signal Meters on Communications Receivers: often have signal meters marked 1 to 9 followed by decibel readings, the chart below provides a conversion to the terminated voltage (in microvolts) at the radio receiver:
Note how relatively small changes in voltage at the lower end of the scale ( in the S1 to S8 range) produce quite noticable swings in the readings, while really quite large changes in signal voltage at the higher end of the scale ( S9 to S+50 ) produce quite small variations in read-out. This non-linear effect is quite intentional: Increases in signal strength from S1 to S9 will produce dramatic improvements in the received signal to noise (S/N) radio while above around the S9+10dB signal level the receiver is approacing the best acheivable S/N ratio and further large increases in signal strength will make less if any improvement to the audible S/N ratio, so the S Meter does not really need to reflect these changes in such minute detail. The signal meter is invaluable when making aerial adjustments and comaprisons as well as being useful for comparing the strength of various transmissions.  RECEPTION REPORTING using the S I O code: With reference to a signal meter on a typical communications receiver, the table below plots the indicated signal strength against the correct reporting code. S = The Signal Level I = The amount of interference O = The (rather subjective) overall quality of the signal. The S and the I parts are indicated below:
O (Overall Quality) is then given as: 5 = Excellent 4 = Good 3 = Fair 2 = Poor 1 = Very Poor almost unreadable THE S I N P O CODE: The SINPO code adds a little more detail by including values for N = Noise and P = Propagation Disturbance. Signal Meters on Hi Fi Tuners: Often some older analogue hi-fi radio tuners included a swinging needle type signal meter to aid tuning on VHF / FM stations. These basic meters provided a rough guide to signal strength, but from experience of various hi-fi tuners that I have used over time the chart below can give some idea of the actual terminated voltage at the tuner's aerial input. The chart below gives a rough approximation:
Required Signal Strength For Acceptable FM Stereo Reception: A top quality HiFi FM tuner will often produce a signal to noise ratio of 60 dB when receiving about 200 microvolts, less than this and reception will be unacceptably noisy. So a deflection on the signal meter of 4 or above is really needed for good stereo. A reading of less than 4 will normally indicate that the tuner should be switched to mono for less noisy reception this is because FM stereo requires up to ten times more signal strength than mono reception to obtain the same signal to noise ratio. To obtain full quieting of around 70 dB, i.e. the best signal to noise ratio, most good tuners would need 300 to 500 microvolts and cheaper tuners and average all in one stereo micro and mini systems etc may need even more than this if little attention has been paid to the tuner circuits. [NB CD audio can achieve 90 - 100 dB signal to noise ratio.] Signal Meters on Hi Fi Tuners With digital dB (Decibels) Read-out: Some Hi-Fi tuners, Sony is one example, have a signal strength read out in dB and while total accuracy cannot be guaranteed, this type of indication will be much more useful than a swinging needle or five LEDs. This readout will give an indication of the Terminated Voltage. To convert the dB figure given in the readout to the actual voltage you will need to use the table shown below: Decibels to microvolts conversion VOLTAGE dB = 20 x Log of Voltage (e.g. 20 x Log of 158uV = 44 dB) (The table below shows results that are reference to 1 microvolt **)
A Note About Calculating Field Strength: If you wish to know the actual field strength in dBuV/m at the point where the aerial is situated you will need to add in some other factors: Feeder Loss in dB: e.g. a certain type of 75 Ohm coaxial aerial cable my have a loss of 10dB per 100 meteres, so if your aerial installation uses 10 meters of coaxial cable then you will have to factor in a 1dB loss. Aerial Gain in dB: A simple dipole may be considered to have zero gain i.e. 0dB, a three element Yagi may have 3dB gain wheras an omnidirectional horizontal circle type aerial could be considered to have minus gain - e.g. -3dB. This figure needs to be taken into account. Termination Loss: Can usually be assumed to be 6dB Effective Length: Usually assumed to be 0dB Example: The terminated voltage at the tuner is 500uV (Log 500 x 20 =54dB) so the field strength when using an aerial with 3dB gain is: 54dB Terminated Voltage -3dB Ae Gain + 0dB Eff Length + 6dB Term Loss + 1dB D'Lead Loss = 58dB Field Strength (i.e. The field strength where the aerial is sited is approximately 794 uV, so there has been a 294 uV loss in the receive aerial system.) TRANSMITTER OUTPUT POWER SCALE DBW [ I always find it useful to remember that when dealing with Voltage that a 6dB increase represents a doubling of the voltage, whereas when dealing with Power a 3dB increase represents a doubling of power - as can be seen in the table below: ] Transmitter powers are usually quoted in Watts, but occasionally they are given in dBW (reference to 1 Watt **). The chart below converts dBW figures to Watts.
[For example if a radio station quotes a transmitter output of 38 dBW just multiply the 30dBW figure (i.e. 1kW) by the 8dBW figure (i.e. 6.4): 1kW x 6.4 = 6.4 kW or if the quoted power is 49 dBW then 10kW x 8 = 80 kW ] DBM
Example calculation (provided by Mark Timlin): To find the power in milliwats for a dBm figure of 62: 62 divide by 10 = 6.2 Antilog 6.2 = 1584893 milliwatts 1584893 x 0.001 = 1584.8 watts N.B. **The Decibel measurement is purely a ratio, it is not an absolute power or voltage. For a decibel reading to be meaningful it must be referenced to a certain voltage or power. If we know that the Decibel measurements are reference to 1 Volt (for example) then we know that 0 dB = 1 Volt and so we therefore can calculate that 6dB = 2 Volts and that 20dB = 10 Volts etc. Similarly with power, if the dB readings are reference to 1 Watt (for example), then we know that 0dB = 1 Watt and therefore that 6dB = 4 Watts and 20 dB = 100 Watts etc. More Information: |
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Don't forget to visit Monitoring Monthly, Radio User and The British DX Club for great articles, reception tips and invaluable information. |
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| LONG WAVE
RECEPTION OF BBC RADIO FOUR IN CENTRAL FRANCE READERS QUERIES Query One: Hello, I found your website when I was trying to source information on how to make my old valve radio work more efficiently. It was my grandfather's and as it was in very good condition I took it with me to France where I live some of the year. I tune the radio in to the Long Wave to listen to BBC radio 4.The problem is that reception is very bad. Only occasionally do I hear the station clearly. Often there is fading and also every kind of crackle in the world drowns out the station. We are situated in the middle of France near Brive. Can I improve the reception? If I took an aerial out on to the roof would this help? Or am I trying to make an old radio work in conditions that are hopeless? I fully understand that I could buy a modern radio,( we have one). I can also at any time listen to any station I want via satellite and on my laptop, but that isn't the point. I would like to receive the BBC on my old radio - which I may add, looks rather grand. If you would be kind enough to give me any advice I would appreciate it very much. Peter Laing Gillies. Possible Aerial Solutions Given a weak signal then there is always something that one can do to improve the situation with regard to a better and more efficient aerial arrangement. If the radio set has an input for an external wire aerial then running a length of insulated wire, say 10 meters or so, outside should improve the strength of the signal. String the aerial wire around a garden or yard if possible, or suspend it from wooden poles fixed to either end of the house so that the wire is a meter or two above roof level. One has to bear in mind that a big aerial can produce large signals from your nearby medium wave and long wave transmitters that may 'swamp' the radio's tuning circuits (RF overload) and produce more noise and different problems. It is worth a go though, and if there are no close by transmitters then an aerial of between 10m and 30 m could be tried. It is always worth experimenting with different aerial locations and orientations to find the best results. However if you are suffering noise in the form of 'every kind of crackle' then obtaining good, or at least better reception can become a little more difficult. Generally a better aerial will not only improve the signal from the required radio station but also proportionately increase the strength of the interference sources. So you will still suffer with the interfering crackles. If the source of the interference is within the house then connecting the aerial to the radio via screened, coaxial, cable may help reduce the amount of interference being delivered to the radio. This will only be of use if the radio has both aerial and earth connection terminals: (Beware of older valved radios - don't try connecting wires internally to the chassis - these radios often have a chassis that is at mains potential and serious electrical shock or death could result.) Connect the inner, | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
