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樓主 |
發表於 21-4-2017 02:12:42
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60m band (5 MHz)
Five (5) MHz RSGB information
This band combines the best characteristics of the 80m (3.5 MHz) and 40m (7 MHz) bands, the 60 meter (5 MHz) band forms a communication bridge when propagation effects make use of 80 or 40m impossible for local-to-medium distance communications – often needed in emergency communication scenarios where there is no existing normal communications infrastructure or it is devastated. Less affected by D-Layer absorption than 80m, the 60 meter (5 MHz) band is an ideal candidate for Near Vertical Incidence Skywave (NVIS), the most commonly used technique capable of providing seamless local-to-medium distance HF communications.
NVIS communication on the 5 MHz band in simplistic general terms is primarily a daytime event commencing at dawn, with peaking signal strengths in the afternoon and the band closing to SSB voice communications shortly after dusk. However there are exceptions to this general rule and it can be possible for NVIS communication to extend in the evening after dark using weak signal data modes such as Olivia 16/500 to around 21:30z, as at March 2013. Later 5 MHz openings to further away stations are possible via the F layer and QSO's inter G from Shetland to Hereford have been open as late as midnight before the band shuts for all inter G comms.
The Primary user in the UK is the Ministry of Defence (MoD), UK amateurs with FULL licences are now allowed to operate on this band, whereas previously you had to have a current Notice of Variation (NoV) to your FULL amateur radio license issued by OFCOM or RSGB. An NVIS antenna configuration is a horizontally polarized (parallel with the surface of the earth) antenna placed low to the ground to ensure a high angle of takeoff, Vertically polarised antennas are not suitable for NVIS as they produce low angles of radiated signals and therefore the skip distance will be too great for local HF communications.
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樓主: VR2GY
