Medium frequency
Frequency range | 0.3 to 3 MHz |
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Wavelength range | 1000 to 100 m |
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Medium frequency (MF) is the
Propagation
Radio waves at MF wavelengths propagate via
MF waves can also travel longer distances via
At night, especially in winter months and at times of low solar activity, the ionospheric D layer can virtually disappear. When this happens, MF radio waves can easily be received hundreds or even thousands of miles away as the signal will be refracted by the remaining F layer. This can be very useful for long-distance communication, but can also interfere with local stations. Because of the limited number of available channels in the MW broadcast band, the same frequencies are re-allocated to different broadcasting stations several hundred miles apart. On nights of good skywave propagation, the signals of distant stations may reflect off the ionosphere and interfere with the signals of local stations on the same frequency. The North American Regional Broadcasting Agreement (NARBA) sets aside certain channels for nighttime use over extended service areas via skywave by a few specially licensed AM broadcasting stations. These channels are called clear channels, and the stations, called clear-channel stations, are required to broadcast at higher powers of 10 to 50 kW.
Uses and applications
A major use of these frequencies is
There are a number of coast guard and other ship-to-shore frequencies in use between 1600 and 2850 kHz. These include, as examples, the French MRCC on 1696 kHz and 2677 kHz, Stornoway Coastguard on 1743 kHz, the US Coastguard on 2670 kHz and Madeira on 2843 kHz.[6] RN Northwood in England broadcasts Weather Fax data on 2618.5 kHz.[7] Non-directional navigational radio beacons (NDBs) for maritime and aircraft navigation occupy a band from 190 to 435 kHz, which overlaps from the LF into the bottom part of the MF band.
An
Many home-portable or cordless telephones, especially those that were designed in the 1980s, transmit low power FM audio signals between the table-top base unit and the handset on frequencies in the range 1600 to 1800 kHz.[10]
Antennas
Transmitting antennas commonly used on this band include
The most common transmitting antennas, monopoles of one-quarter to five-eighths wavelength, are physically large at these frequencies, 25 to 250 metres (82 to 820 ft) requiring a tall
Lower power transmitters often use
Receiving antennas do not have to be as efficient as transmitting antennas since in this band the
See also
- Electromagnetic spectrum
- Global Maritime Distress Safety System
- Maritime broadcast communications net
- Navtex
- Types of radio emissions
References
- ^ "Rec. ITU-R V.431-7, Nomenclature of the frequency and wavelength bands used in telecommunications" (PDF). ITU. Archived from the original (PDF) on 31 October 2013. Retrieved 20 February 2013.
- ISBN 0471743682.
- ^ "Ground wave MF and HF propagation" (PDF). Introduction to HF Propagation. IPS Radio and Space Services, Sydney Australia. Retrieved 27 September 2010.
- ^ "United Kingdom Frequency Allocation Table 2008" (PDF). Ofcom. p. 21. Retrieved 26 January 2010.
- ^ "U.S. Frequency Allocation Chart" (PDF). National Telecommunications and Information Administration, U.S. Department of Commerce. October 2003. Retrieved 11 August 2009.
- ^ MF/HF SSB Frequencies Archived 6 September 2007 at the Wayback Machine
- ^ Amended Radiofax schedule
- ^ U.S. Government Frequency Allocation Chart
- ^ "The 500 KC Amateur Radio Experimental Group". 500kc.com. Retrieved 5 April 2018.
- ^ "totse.com - How to listen to cordless telephone conversations". 6 January 2009. Archived from the original on 6 January 2009. Retrieved 5 April 2018.
Further reading
- Charles Allen Wright and Albert Frederick Puchstein, "Telephone communication, with particular application to medium-frequency alternating currents and electro-motive forces". New York [etc.] McGraw-Hill Book Company, inc., 1st ed., 1925. LCCN 25008275
External links
- Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).