Tuesday, 29 November 2011

The 4-metre (70 MHz) band.

The 4m band is an amateur radio frequency band in the lower Very High Frequency (VHF) spectrum.
Before World War II, British radio amateurs had been allocated a band at 56 MHz. After the war ended, they were allocated the 5-metre band (58.5 MHz to 60 MHz) instead. This only lasted until 1949, as by then the 5-metre band had been earmarked for BBC Television broadcasts.
In 1956, after several years of intense lobbying by the Radio Society of Great Britain (RSGB), the 4-metre band was allocated to British radio amateurs as a replacement for the old 5-metre band allocation. For several years the 4-metre band allocation was only 200 kHz wide—from 70.2 MHz to 70.4 MHz). It was later extended to today's allocation of 70.0 MHz to 70.5 MHz.
A small number of countries in Europe and Africa have also allocated the 4-metre band to radio amateurs as a result of the decline in VHF television broadcasts on the 4-metre band. 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 and because very few countries have an allocation there, very little dedicated commercial amateur equipment is available. Therefore most amateurs active on the band are interested in home construction or modification of private mobile radio (PMR) equipment. 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.
It ranges from 70 MHz 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-metre 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 the 6-metre band, 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 long distance (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.
First ever TEP qso on 70mhz took place on 28 March 2011 between SV2DCD Leonidas Fiskas and ZS6WAB Willem Badenhorst
Access to the 4-metre band has always been limited by access to suitable 4-metre transceivers. A limited number of transceivers were purposely built for amateurs on this band while converted Private Mobile Radio equipment is in widespread use e.g. Phillips FM1000 and the Ascom SE550
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. 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 (31 mi) or so with simple antennas.
In the Sporadic E seasons communication around Europe is possible with such equipment. Currently, the only Japanese-made, "mass-market" amateur radio transceiver to cover the Four metre band as standard is the UK specification Yaesu FT-847 which was discontinued in 2005. Because of this, many 4-metre users gain access to the band by using converted "Low band" VHF ex-PMR (Private Mobile Radio) transceivers but invariably these only have either AM or FM and those users who prefer to have a multi-mode capability but can't afford a second hand Yaesu FT-847 normally use transverters, either purposely built home builds or sometimes even converted 6-metre or 2-metre versions.
In recent years there have been extensive imports of Chinese PMR transceivers such as the Wouxun KG-699E 4m (66 MHz-88 MHz) and KG-UVD1P1LV DUAL BAND (TX/RX 66-88 Mhz /136-174 Mhz) Handheld Transceiver to Western countries mainly so far in the UK and mainland Europe.
But in recent months Qixiang Electronics, the makers of the AnyTone and MyDel transceivers have exported the AnyTone 5189 PMR 4m (66 MHz-88 MHz) transceiver from China to the UK and to Europe.
Both Transceivers have been selling extensively well in the UK and in Europe.
There also have been rumours about a 4m/6m dual band multi-mode transceiver being released in late august or early September. It is not known at this time who is manufacturing this transceiver.

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