4 metres
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4 metres (4 m, 70 MHz) is an amateur radio frequency band in the lower Very High Frequency spectrum. Traditionally only allocated in a small number of countries in Europe and Africa, the decline in VHF television broadcasts, movement away from the old Eastern European VHF FM broadcast band and migration of commercial stations to higher frequencies have led to slow but steady growth in the number of countries where 4 metre operation is permitted.
The 4 metre band has a unique character, because very few countries have an allocation there, very little commercial equipment is available, and therefore most amateurs active on the band are interested in home construction. As a result there is a lot of camaraderie on the band and long ragchews are the norm, as long as there is some local activity.
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[edit] Allocations and propagation
It ranges from 70 to 70.5 MHz in the United Kingdom, with other countries generally having a smaller allocation within this window. The 4 Metre band shares many characteristics with the neighbouring 6 metres band. However, as it is somewhat higher in frequency it does not display the same propagation mechanisms via the F2 ionospheric layer normally seen at HF which occasionally appear in 6 metres, leastwise not at temperate latitudes. However, Sporadic E is common on the band in summer, tropospheric propagation is marginally more successful than on 6 metres, and propagation via the Aurora Borealis and meteor scatter is highly effective.
While Sporadic E permits Europe wide communication, it can be a mixed blessing as the band is still used for wide bandwidth, high power FM broadcasting on the OIRT FM band in a declining number of Eastern European countries. Although this is has lessened in recent years, it can still cause considerable interference to both local and DX operation.
As of 2005, no communication has taken place on the 4 metre band between Europe and Southern Africa, although theoretically this ought to be possible by stations with amateur power and antenna sizes around the equinoxes. It is to be hoped that the increasing availability of the band in Mediterranean countries, where the trans-equatorial path is less difficult than from the bands traditional strongholds in Britain and Ireland, might spur such interest.
[edit] Equipment and power
Some low power FM commercial equipment is available for the band, although it is of relatively simple specifications as generally suitable for communication of up to around 50 kilometres or so with simple antennas, in the Sporadic E seasons communication around Europe is possible with such equipment. A limited number of transceivers were purpose built for amateurs on this band, while converted Private Mobile Radio equipment is in widespread use. For more reliable DX performance, however, at least some equipment must be home constructed, and the most popular route is usually to use a 10 metre or 6 metre commercially made transceiver followed by a home built transverter.
In most countries, the maximum power permitted on the band is lower than in other allocations, to minimise the possibility of interference with non-amateur services, especially in neighbouring countries.
[edit] Activity
In some parts of the UK the band is little utilised, while in others, notably Belfast, Bristol, South Wales, North London and Hertfordshire, there is extensive local FM operation. There is considerable AM activity in the Dublin area. As band occupancy is relatively low, FM operation tends to take place on the calling frequency, 70.450 MHz, and AM operation on that calling frequency, 70.260 MHz. In the UK, the band is also used considerably for emergency communications, Internet Radio Linking Project links (IRLP), data links and low powered remote control.
In continental Europe the band is still primarily used for more serious DX operation. Cross-band working with 6 metres or 10 metres is common to make contacts countries where the band is not allocated.
[edit] Countries in which 4 metres is allocated
In May 2006, the 4 metre band was allocated in the following countries:
- "traditional" 4 metre countries - the United Kingdom, its dependencies of the Isle of Man, Guernsey, Jersey, Gibraltar and the Sovereign Base Areas on Cyprus, in the Republic of Cyprus, the Republic of Ireland, South Africa and Namibia.
- "new" 4 metre countries - Croatia, Denmark, the Faroe Islands, Greece, Greenland, Luxembourg, Monaco, Portugal, Slovenia and Somalia.
- "possible" 4 metre countries - Romania and Serbia, where amateurs have been active in the Sporadic E season and apparently have received informal permission from their communications regulators to operate on a trial basis, although no official publiciation to that effect has been made.
There are active campaigns to secure 4 metre privileges in Austria, Italy, Sweden and Finland.
The February 2006 edition of British amateur radio magazine, Radcom, reported that Dutch amateurs are likely to be given 4 metre privilleges when the last Dutch VHF Channel 4 TV transmitter closes down later in the year.
[edit] Band Plans
[edit] Radio Society of Great Britain 70 MHz Band Plan
70.000 - 70.050
Beacons only
70.030
Personal Beacons
70.050 - 70.250
Narrow Band modes
70.085
PSK31 centre of activity
70.185
Cross-band activity centre
70.200
SSB/CW calling
70.250 - 70.300
All modes
70.260
AM/FM calling frequency
70.300 - 70.500
All modes channelised operation with 12.5 kHz spacing
70.300
RTTY/fax calling/working
70.3125
Digital modes
70.325
Digital modes
70.3375
Digital modes
70.350
Digital modes
70.3625
Digital modes
70.375
FM Simplex
70.3785
Internet voice gateway
70.400
FM Simplex
70.4125
Internet voice gateway
70.425
FM Simplex
70.4375
Digital modes
70.450
FM Calling frequency
70.4625
Digital modes
70.475
FM simplex
70.4875
Digital modes
(Source: The Four Metres Website)
[edit] Common Uses of 4 meters
[edit] External links
| Very high frequency (VHF) and Ultra high frequency (UHF) Amateur radio bands | |||||||
| VHF | UHF | ||||||
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| 6 m | 4 m | 2 m | 1.25 m | 70 cm | 33 cm | 23 cm | 13 cm |
| 50 MHz | 70 MHz | 144 MHz | 219-220 MHz | 420 MHz | 902 MHz | 1.24 GHz | 2.3-2.31 GHz |
| 54 MHz | 70.5 MHz | 148 MHz | 222-225 MHz | 450 MHz | 928 MHz | 1.3 GHz | 2.39-2.45 GHz |
