FMD55 1999 Page 2
12.11. Propagation of SW Signals
One of the questions raised frequently is to determine which
transmissions can be received at what distance from the
transmitter. There is a number of factors that affect Short Wave
reception and distance vary greatly depending on time of day
and year, sun activity and amount of traffic in a particular band.
Each band has its own characteristics and as a rule of thumb one
could say ‘the higher the frequency, the higher the distance’, at
least during day time. At night there is also a considerable
increase in the distance for low frequency bands. For instance, a
typical transmitter in the 4 MHz band would cover a distance of
250 n.m. around noon time which would increase to as much as
2,500 n.m. at night. The following comparison looks at the various
bands their respective propagation characteristics.
2 MHz Band: Maximum distance during day time is about 60 n.m.
which increases at night to 200 n.m. under good conditions.
Thunder storms and lightning severely affect reception quality.
4 MHz Band: Reception in this band works best in the early
morning hours with a gradual decline towards noon time.
Towards the evening propagation may exceed 2000 n.m..
Reception of transmitters in closer proximity may not be possible.
8 MHz Band: Best propagation during the early morning hours.
Distances up to 800 n.m. should be possible during the entire day.
Reception of transmitters in closer proximity may not be possible.
12 MHz Band: Until late afternoon no long distance coverage.
Thereafter propagation increases gradually but transmitters
located within 600 n.m. may not be received.
16 MHz Band: This band is similar to the 12 MHz band. Reception
of stations within 800 n.m. is not normally possible. In the late
evening hours propagation increases to 6000 n.m..
22 MHz Band: This band is not normally usable for stations located
within 1000 n.m.. under good atmospheric conditions distances of
up to 8000 n.m. may be covered. Best connections are obtained
in North / South direction. Right after sunset this band is not
usable.
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