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DX-ing and
Short Wave Radio

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DX-ing AND SHORT WAVE RADIO


Short Wave / H.F. Radios:


Target HF3 short wave HF receiver
Target HF3 short wave HF receiver

TARGET HF3 AM/SSB COMMUNICATIONS RECEIVER   "There is no greatness where there is no simplicity." (Leo Tolstoy)

I am often asked what would be a good H.F. receiver. There are quite a number to choose from and having previously owned a Lowe HF-150 which has now sadly been discontinued, I think that the Target HF3 could now make a very interesting proposition. I particularly admire the simplicity of its appearance. As Leonardo da Vinci noted; "Simplicity is the ultimate sophistication."

Spectrum Communications are the dealers for the Target HF3 receiver (2012) and Tony Nailer comments: "This is a masterpiece of RF engineering covering the entire spectrum between 30KHz to 30MHz. The receiver is supplied with a comprehensive instruction manual, which includes a list of useful marine frequencies. Controls on the front of the receiver change reception mode, from a narrow filter for SSB reception to a wide filter, which enables high quality AM signals to be received from broadcast stations around the world. They also control ten memory channels to store your favourite frequencies. The receiver uses a 45MHz first IF and has a high side fully synthesized local oscillator providing exceptional stability.  A large, clear liquid crystal display shows the precise receive frequency.  It has a fixed level audio output to connect to a computer sound card. Supplied with a basic wire antenna and 12 volt power cable."  To conclude I will recall Albert Einstein who noted: "Everything should be made as simple as possible, but not simpler."

Tune in to short wave radio broadcasts - check stations and frequencies at  www.shortwaveschedule.com



Some other previously available short wave (HF) radios:

Sony radio
Sony  ICF SW 7600 GR


Roberts radio
Roberts R9914

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.

The Palstar R30 Communications Receiver is for the serious Short Wave Listener who wishes to catch some exotic DX, it's easy to use and offers high performance and excellent value for money!  Click HERE to find out more.

Some other 'classics':


Lowe HF-150


Lowe HF-225

TARGET (AKD) HF3
Above are the Lowe HF-150 and HF-255 communications receivers, high quality classics that will be sadly missed now that Lowe Electronics have recently discontinued production of radios in Britain.  The excellent little HF3 was, until 2003, produced by AKD Products of Stevenage.  AKD Products produced the HF3 receiver together with a number of other communications products such as RF filters, but have now ceased trading.  The rights to the AKD range have been aquired by Garex Electronics www.garex.co.uk who will be marketing some of the former AKD products and, perhaps, the HF3 too.


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.


photo
A "Listening Post" Including HF Receiver and Scanner for VHF & UHF
[Click on the picture to see some more ideas about aerials on the Lowe HF-150 page!]

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.

Tuner
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
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.

Grundig Satellit 2000 radio
Vintage Grundig Satellit multiband radio


AERIALS:

No matter how good your radio it must be fed by a good antenna!!

For Medium Wave and Long Wave
Portable loop
Long Wave Frame Frame Aerial
Portable Medium Wave Loop
Long Wave Frame Aerial
Constructional Diagram

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.

An Aerial For Short Wave
CLICK
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.)

For portable radios:

This random wire aerial could be connected directly to the receiver's aerial socket if it has one.  If the radio has no aerial socket then the aerial could be clipped directly onto the telescopic rod with a crocodile clip, but both of these options could overload a portable radio's tuning circuits and while not harmful it will cause much undesired noise and interference.

It is usually much more effective to indirectly couple the aerial to the radio:  Wind the last few centimeters of aerial wire into about 6 to 20 turns around a paper tube and slide this over the telescopic aerial and adjust its position along the rod until the best signal coupling is found.  Sometimes even better results are obtained by connecting the free end of the wire to earth.

Aerial Coupler

Illustration shows a method of coupling a wire aerial to a radio with no aerial socket.

A better option is to connect the aerial to a portable radio's antenna socket via an ATU - see below

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.

ATU
An Aerial Tuning Unit
A better method of coupling a long random wire aerial to a short wave radio that has an antenna socket is to use an Antenna Tuning Unit that also incorporates an attenuator to reduce the signal if neccesary.  An ATU can help match the widely varying impedence of a random length of wire to the fixed 50 ohm impedence present at the input of the radio.  By better matching the aerial to the radio more of the signal collected by the aerial will be transferred to the radio.  

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:

INTERNATIONAL BROADCAST HF BANDS

AMATEUR HF BANDS
Meter Band
Frequency  (MHz)
Meter Band
Frequency  (MHz)
120
2.30 - 2.495 'Tropical Band'
160 ("Top")
1.80 - 2.00
90
3.20 - 3.40   'Tropical Band'
80
3.50 - 3.80
75
3.90 - 4.00   Europe, Asia, Africa
40
7.00 - 7.20
60
4.750 - 5.060   'Tropical Band'
30
10.10 - 10.15
49
5.800 - 6.200
20
14.00 - 14.35
41
7.200 - 7.450
17
18.068 - 18.168
31 - heavy use
9.400 - 9.990
15
21.00 - 21.45
25
11.60 - 12.10
12
24.89 - 24.99
21
13.57 - 13.87
(CB Radio)
26.96 - 27.99
19
15.10 - 15.80
10
28.00 - 29.70
16
17.48 - 17.90


15 - rarely used
18.90 - 19.02


13
21.45 - 21.85


11 - DRM?
25.60 - 26.10


(N.B. 1000kHz = 1MHz)

Domestic Broadcasting:

DOMESTIC BROADCAST BANDS
Band / Use
Frequency (MHz)

Band / Use Frequency (MHz)




Long Wave / AM Radio
0.15 - 0.28
Band III Television (Not UK) 175 - 210
Medium Wave / AM Radio
0.51 - 1.62
DAB / Digital Radio 209 - 216
Band I  / Television (not UK)
48 - 67
Band IV and Band V / Television 470 - 860
Band II VHF / FM Radio
87.5 - 108




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:

Signal
1
2
3
4
5
6
7
8
9
9
+10dB
9
+20dB
9
+30dB
9
+40dB
9
+50dB
uVolts
0.2
0.4
0.8
1.6
3.2
6.3
12.5 25
50
158
500
1580
 5000
15.8mV

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.

Lowe HF-225 signal meter


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:

Signal shown on meter
S
as reported in the SIO code
Amount of Interference
I
as reported in the SIO code
1 to 3 (v. weak to weak)
1
Extreme
1
4 to 7  (fair to good)
2
Severe
2
8 to 9 +10 (strong to very strong)
3
Moderate
3
9 +20 to 9 +30dB (very strong)
4
Slight
4
9+40 to 9+60dB (extremely strong)
5
None
5

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:

SIGNAL METER READING
(vhf / fm)
1
2
3
4
5
Microvolts
(approximate)
5 - 10
10 - 20
30 - 80 160 - 250
500- 1000

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 **)
dB
2
3
4
6
8
10
12
14
16
18
20
22
24
uV
1.25
1.4
1.6
2
2.5
3.2
4
5
6.4
8
10
12.5
16














dB
26
28
30
32
34
36
38
40
42
44
46
48
50
uV
20
25
32
40
50
64
80
100
125
158
200
250
318














dB
52
54
56
58
60
62
64
66
68
70
72
74
76
uV
398
500
630
794
1000
1260
1580
2000
2500
3200
4000
5000
6400


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. 

dBW
0
1
2
3
4
5
6
7
8
9
10
20
30
40
50
Watts
1.0
1.25
1.6
2.0
2.5
3.2
4.0
5.0
6.4
8.0
10
100
1kW
10kW
100kW

[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

dBm
1
10
20
30
40
50
60
milliwatts
1
10  (0.01 watt)
100  (0.1 watt)
1,000  (1 watt)
10,000  (10 watts)
100,000  (100 watts)
1,000,000  (1 kW)

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.


Panasonic RF-3100 Short Wave H.F. Antenna Installation and Propagation Advice:

Panasonic RF-3100 Short Wave H.F. Antenna Installations

Panasonic RF-3100 Short Wave H.F. Antenna Installations
Panasonic RF-3100 Short Wave H.F. Antenna Installations


Panasonic RF-3100 Short Wave H.F. Antenna Installations

Panasonic RF-3100 Short Wave H.F. Antenna Installations
Above: Panasonic RF-3100 Short Wave H.F. Antenna Installation Advice


More Information:
button Loop Aerial & ATU Constructional Pages - Make your own reception aids!
button Lowe Electronics HF series of Communications receivers
button Radio Stations & Memorabilia
 
Don't forget to read Practical Wireless MagazineRadio User Magazine  and join  The British DX Club for great articles, reception tips and invaluable information.







NUMBERS STATIONS

Emails from Gary Hagermann:

"Good Afternoon Mike,

Just a short email to express my appreciation of a very interesting site. I am a recently early retired radio enthusiast, having picked up radio as a ten year old, and now, at 65 years of age, I have to say it is getting b---dy heavy, but I still won't put it down.

My British Army tour of 1964 to 1971 as a Regular, and my Reserve Service of 1972 to 1984 saw me continue this interest, and all at someone else's expense! Neat, huh? I particularly enjoyed your clip on Number Stations [see below] as I belong to ENIGMA 2000, a Group which specializes in these and other Military and Intelligence related communications modes. They are still alive and well, although not so prolific as in recent years, the Cold War in particular.

They abound in CW (Morse), voice, and various data transmission modes. If you wish, I will send you a frequency prediction list which is produced by Ary Boender, one of our members. [Shown below]

Enigma 2000 Newsletter
Download a Sample Newsletter here
Visit Enigma 2000 for the latest news at the URL:
http://www.enigma2000.org.uk


I also enjoyed your various radio receiver reports. I have a Yaesu FRG 7700 with a long wire aerial into a FRT 7700 aerial tuner and FF5 notch filter. I use my desktop PC for recording, but it is daisy chained into a cassette recorder and a reel to reel tape recorder for off air recording. (I know, it sounds like Marconi's coffin in this shack!) I also have a Grundig Yacht Boy as a stand by and portable rig.

I am trying to bring an old R1155N back to life, but the Force is not as strong as once it was!

Well, some short email, but I did love the site, and will be back.

Very best wishes to you and the family, and Best DX.
73 de Gary."    
[January 31st 2012]


Thanks for all the information Gary, it's all absolutely fascinating. Much appreciated, Mike

More from Gary.....


"Hello Mike,

Today I took delivery of my brand new Eton Satellit 750. Got it up and running in the shack as I type. Really does make the winter seem a bit more bearable. (Yeah, well, I know that is an exaggeration!)

Hope you get some joy with the number stations. The stations marked as X or XPA are data transmitters. One of the guys has written a program to decrypt it into numbers/letters, but as you know, decrypting the actual message is a complete no-hoper. We think the numbers and/or letters must be for one time pads or a derivative of them. A book code is possible, given the amount of literature is knocking about the world.

As an Intelligence Corps sergeant said to me; "Just because the message is sent in English, German or whatever, only proves the sender and receiver understand enough to send numbers/letters in that language." This was circa 1966 and all was black and white to me then! I had just said something like; "If this is a German message, must be for a German, huh Sarge?" Oh foolish youth!!

Let me know how you get on.

If you want some other frequencies, USAF have a worldwide HF net and 11175 USB is a good one to listen out on.

There are more, but my addled brain needs a book to refresh it! If you get a string of NATO phonetics, it is an EAM or emergency action message. Another one they send is "Skyking." Both are in the deepest of encryption, so no chance of cracking that either! Just as well, a lot of my family are American, and I have no wish to see the other side of Cuba! (As in Gitmo Bay!)

Best DX and 73 de Gary Hagermann"

Thanks again Gary!  Best wishes, Mike.





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, centre conductor of the cable to the aerial/antenna input of the radio and the outer braided conductor of the cable to the earth/ground terminal.  Run the coaxial cable from the radio to a point outside the house/building several meters away from the boundary of the building.  This keeps any interference originating from inside the house away from the aerial.  Then connect 10m to 30m of pvc insulated wire to the centre conductor of the coaxial cable and place it high up away from the house.  The outer braid of the coax cable can be connected to an earth stake a few feet long that has been driven into some damp soil - this may help take any interference picked-up inside the house on the braided part of the coaxial cable down to earth.

The use of an ATU may help with matching the aerial and coaxial feeder to the radio, as might the use of a matching transformer at the junction between the aerial wiore and its point of connection with the coaxial cable.  See the ATU page HERE.

The other possibility is to use a large frame aerial.  Make a frame aerial about 1meter square or larger if possible.  The advantage of a frame aerial is that, although it does not pick up as much signal as a long wire aerial, it is very directional and can be rotated to either give the highest signal from the wanted station or to reduce to a minimum (null out) an interfering station or source of noise.

A frame aerial can be extremely effective for reducing interference, however if the source of the interference is from within the house then it made carried and radiated by internal wiring and could come from all sorts of different directions and the directional properties of a loop may not be so useful.  It is still worth a try though, so see our loop/frame aerial page HERE.


Query Two (A similar question):

Hi there

I found your interesting site whilst browsing the web looking for information on getting better quality MW and LW radio reception whilst travelling around W and C France.  I spend quite a lot of time near Bordeaux and would really like to be able to pick up british stations on these frequencies.  My existing portable radio is now pretty dead after many years of use. I was wondering if you had any suggestions on which models could make a good replacement?

Many thanks,  Jon

Reply

Hi Jon,


Long distance stations will certainly come in better at dusk, night and early morning. I listened to Capital Radio from London many many years ago in central France at these times.

I cannot guarantee that you would get medium wave stations from the UK during the day, but the use of a loop aerial may be well worth a try. I would certainly expect to be able to get Radio Four on Long Wave during the day using a loop aerial in central France.

My general advice would be to use a good quality receiver from a well known manufacturer, i.e. Sony, Panasonic, Sangean / Roberts (Roberts re-badge Sangean radios and tend to be more expensive than the Sangean equivalent.) and just as importantly, is to use an effective aerial. I would recommend a loop aerial of approximately 14 inches in diameter for travel use.

Rather than buy a new radio first off, I would make the loop aerial. However you cannot buy them, but if you are quite good at using a screw driver, pliers and saw etc and think that you could turn your hand to some easy soldering (i.e. a bit of very simple DIY) then it should not be very difficult to make a loop aerial - well two aerials actually would be more effective - one that will tune across the medium wave band and another that could be fixed to 198 kHz long wave for BBC Radio Four.






Short Wave Radio - Amateur Radio and Citizens Band Radio Under Threat
From "HomePlug Networking" Broadband by Powerline Devices
SHORT WAVE (H.F.) RADIO, INCLUDING AMATEUR RADIO, IS THREATENED WITH MASSIVE AMOUNTS OF INTERFERENCE CAUSED BY British Telecom's BT HomeHub / Vision PowerLineAdapters & OTHER SIMILARLY UNNECESSARY  'B.P.L' & 'PLT' PRODUCTS.

Radio interference from BT Home Hub / Vision PowerLine Adapters and other similar devices could also threaten YOUR broadcast radio reception with vast amounts of radio interference.

More Information >>





FOOTNOTE:  SOME INTERESTING OLD FREQUENCIES

Below are some frequencies identified in an old Lowe Listeners Guide.  Some of them can still reveal very interesing results particularly in Marine or Air communications.  Most of these frequencies lie outside the general Broadcast Bands so many will use the Sideband mode of transmission.  Usually Lower Lideband (LSB) for frequencies below 10MHz and Upper Sideband (USB) for frequencies above 10MHz.

If you want to listen to general broadcast programmes then consult THE BANDS table above, but before you go there just have a tune around in the space between those broadcast bands - it can be fascinating, but don't expect to hear something immediately and do remember that this is now a very old list.......

3366KHz
Ghana Broadcasting. This is an excellent test station to see if this classic DX band is open. Try around midnight. As we slowly creep up the HF spectrum, signals penetrate the E Layer only to be reflected down again by the F Layer. As this layer is twice the height of the E Layer, the reflected signal comes to your antenna from a much greater distance. This effect is what gives 80m its European coverage by night. By day it remains The Great UK Natter-band.

3650KHz
Allocated frequency for GB2RS RSGB UK News. Costing over £5000 a year to run, the future of the RSGB News is under constant review. For the writer, the first sideband station he resolved, for the new generation of radio ham something of an anachronism. Stalwarts only need listen for useful reports of solar activity - if you can understand them - details of Club Events and radio rallies in the summer. The writer has been out of Ham Radio for years but still finds himself listening on Sundays at 0930z. We miss you, Fred G2CVV..

The 4Mhz Land/Marine Mobile Band

4125KHz: Marine Distress International.

4138KHz: Arctic Seas Distress

4138KHz: Arctic Seas Distress.

4220KHz: Arctic Seas Supplementary.

4594KHzNumbers station.

The return of the number stations may have a lot to do with conditions, but the routines suggest mere testing of old equipment, a lot of transmissions being in AM.

4742KHz RAF Flight Watch: "Architect listening out."

Architect is the Flight Watch callsign. Despite all the new technology, the main enemy to operations is the weather. This code is given at fixed times and upon request to pilots preparing to fly between British airbases. From this we will learn that a Wattisham Blue has little to do with being an all-round good egg while up at University, but "Forever Amber" is a good status for most of my holidays in Wales. Other flight watch frequencies are included in the lists. Serious HF airband operation will need one of the better receivers with a stable sideband operation and a large number of memories to allow rapid channel hopping.

4750KHz
The lower limit of the 60m Tropical Band. Allocated only in the tropics, this band gives up some musical treats in the late evenings. And it's getting better;

4770KHz
Radio Nigeria. Long today's dance trends set the nations feet to dance to the urgent guitars of World Music via BBC Radio 1, those of us blessed with short-wave could hear the opium of the people on The Tropical Band without the need for mosquito nets and funny injections...

4882KHz
Letter Station. Just as the reviewer sharpens his pencil to have a go at the endless entries for so-called "number stations", the ionosphere rings the changes with a station sending five letter groups.

This one sends IOBMJ, "India/Oscar/Bravo/Mike/Juliet" ad nauseam.

5080KHz
East Coast Control.

5095KHz
Buchan Control. Examples of Air Defence Radar Units.

6211KHz: Northern Seas Supplementary Distress.

6215KHz: Marine Distress.

6224KHz: Thames Control.

Many Sunday Pirates have moved to the 75 Metre band.

6300KHz
Russian number station. "Golly, Control, you don't think they are at it again?"

No, we don't. The modulation quality suggests some very old plant is just being given an airing. They tell us the price of freedom is eternal vigilance, so you never can tell...

6622KHz
Shannon ATC. Secondary calling on 8831.

7265KHz
Sudwestfunk, Baden-Baden, Germany. Real radio as a public utility. Nothing but a rich mix of pop and rock from albums, news, weather and travel information. Listen for the pulse of RDS data that switches over a million German radios to this network for the latest update.

7860.5KHz Army Signals. "That man there! Absolute shower!"

The 8Mhz Mobile Band

Including:

8228KHz: Ostende Radio.

8291KHz: Marine Distress.

8634KHz: Ships Survival Craft.

8737KHz: Cyprus Maritime Radio Service.

8825KHz: North Atlantic Control.

8846KHz: New York Radio. Secondary calling on 6577.

8864KHz: Shannon ATC.

8879KHz: Shannon ATC.

8891KHz: Shannon ATC.

8957KHz: Shannon Volmet.

9031KHz: RAF Flight Watch and Gibraltar Forward Relay.

9251KHz: "The Lincolnshire Poacher". Classic English number station.

9830KHz: Croatian Radio. News heard at 0800.

10000.0KHz
Calibration Beacon. Many countries compete to provide a Reference Standard, so much so that 10000 is merely the middle of a standard's sub-band. The one you find could be up to 5KHz away from what you take to be 10000 leaving you to question the accuracy of your radio. Chances are that if it was made in the last decade of synthesizer design, then all will be well. Standards can confuse as well as assist...

An example: Callsign RWM from Moscow is the strongest SFS station in Europe and can be heard on 4996, 9996 or 14996kHz throughout the 24 hours. It sends five minutes of unmodulated carrier, five minutes of one second pulses and five minutes of one tenth second pulses. The latter have to be unfiltered with a sharp leading edge for precision purposes, which results in key click splatter being heard around the world. For frequency calibration and propagation checking purposes these SFS stations are ideal, but don't forget that radio signals take around one seventh of a second to travel around the world. The timing is, however, sufficiently precise for meteor scatter schedules.

10051KHz: New York Radio.

111660KHz: Radio Australia (recprion from about 3pm in England - added 2005 by Roger Sharp).

12290KHz: Marine Distress.

12392KHz: Marine World-wide Calling and Distress.

The 13Mhz Long Distance Mobile Band

The major world-wide mobile communications band;

13146KHz: Portishead Radio. Traffic and Weather on the hour.

13270KHz: New York/Gander Radio.

16420KHz: Marine Distress.

18930KHz: WEWN.



Happy listening and good DX,
Mike


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