70 МГц жиілік диапазоны: әуесқой радио байланысының ерекшеліктері

Amateur radio frequency band

The 4 metre (70 MHz) band is an amateur radio band within the lower part of the very high frequency (VHF) band. As only a few countries within and outside of Europe have allocated the band for amateur radio access, the availability of dedicated commercially manufactured equipment is limited. Most radio amateurs active on the band are interested in home construction or the modification of private mobile radio (PMR) equipment. As a result, communication on the 4 metre band tends to focus on technical topics, with long 'rag chews' being the norm as long as there is some local activity.

The 4 meter band, occupying the 70 MHz frequency range, has been historically significant for various regional radio services. Post World War II, the United Kingdom allocated a segment of the band, specifically 56 68 MHz, to British community radio stations, a provision that lasted until 1949. This allocation was subsequently reassigned for television broadcasting by the BBC. Later developments saw the band's usage extend to France until 1961. The Radio Society of Great Britain (RSGB) was instrumental in advocating for the allocation of the 4 meter band to British community radio stations in 1956, replacing the 5 meter band. This reallocation provided a mere 200 kHz bandwidth initially, from 70.2–70.4 MHz. It wasn't until later years that the allocation expanded to the current standard of 500 kHz, ranging from 70.0–70.5 MHz. International attention to the 4 meter band increased during the International Geophysical Year of 1957–1958, with several European countries being assigned frequencies within the 70 to 72.8 MHz spectrum.

During the 1990s, the European Radio Communications Office (now ECC) of the CEPT conducted a thorough spectrum analysis, which included the 4 meter band among other frequencies. The investigation's findings, published in 1995, recommended the consideration of the 70 MHz frequency as an amateur radio band, aligning with existing amateur radio service allocations. For a detailed overview of country specific allocations within the 4 meter band, refer to the comprehensive table updated regularly on the Four Metres Website (70MHz. org).

The 4 meter band is gaining traction across various regions, with usage extending to amateur radio operators in Europe and Africa. Historically limited to the UK, Gibraltar, and British Military Bases in Cyprus, the band's allocation has evolved due to changes in technology and regulatory stances. The CEPT's recognition of the band for amateur radio use, facilitated by the regulatory footnote "ECA9," has been a significant factor in this growth. CEPT administrations may now authorise the band's usage between 69.9–70.5 MHz for amateur services on a secondary basis[1]. Regular updates on the allocations are provided on the dedicated Four Metres Website (70MHz. org), reflecting the dynamic nature of frequency management[2].

Access to the 4 meter band is somewhat limited due to the scarcity of commercially produced transceivers specifically for this range. However, enthusiasts often utilise equipment that was originally designed for other purposes, modifying it to suit the 70 MHz band. For instance, devices like the Philips FM1000 and the Ascom SE550, while not expressly made for the 4 meter band, are popular among hobbyists for their adaptability and sufficient range for local communications[1]. Historically, there have been purpose built amateur radio transceivers for the band, but these are less common today. Notably, some amateur radio operators have repurposed equipment to access the 4 meter frequencies, demonstrating the innovative spirit of the community[2].

In the UK the band has a mix of AM, FM and DX activity, assisted by the recent support for 70 MHz in newer amateur radio equipment. In the UK, the band is also used for emergency communications, Internet Radio Linking Project links (IRLP), data links and low powered remote control.

There is considerable AM activity in the Dublin area. As band occupancy is relatively low, FM operation tends to take place on the 70.45 MHz calling frequency, and AM operation on the 70.26 MHz calling frequency.

In Europe the band is still primarily used for more serious DX operation. Cross band working between the 6 metre band or the 10 metre band is common to make contacts countries where the band is not allocated.

During the European summer season, the band is frequently open for DX work across the continent, with the centre of activity for long distance voice and digital/data communication situated in the lower part of the band. The compact size of both horizontal and vertical antennas designed for the 70 MHz band is beneficial to radio amateurs who enjoy DX work but have insufficient space for larger multi element antennas designed for lower frequencies. DX voice traffic in SSB mode can be found around the SSB calling frequency of 70.2 MHz, whereas AM/FM contacts tend can be initiated at the 70.26 MHz AM/FM centre of activity. When the band conditions are poor or in cases where stations operator are able to transmit with modest power levels only, modern digital modes, capable of decoding transmissions down to a 12 dB s/n level, such as PSK31, Thor or Olivia, still permit reliable keyboard to keyboard free text communications at relatively large distances. Other more resilient digital modes capable of decoding signal down to 20 dB s/n, such as FT8, JT9 and JT65, offer reliable signal report exchanges at distances of up to several hundred or several thousand kilometres, depending on band conditions.

United States has one experimental transmitter, station WE9XFT in Virginia, transmitting CW on 70.005 MHz. The beacon continues to be operated under the Experimental radio service call sign WG2XPN and is active as of March 2021. A petition was filed with the U. S. Federal Communications Commission on 27 January 2010 to create a new U. S. 4 meter amateur radio allocation at 70 MHz to parallel those in Europe and other parts of the world. This petition was subsequently rejected by the FCC.