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Type of Radio Wave Propagation
Frequency Band
Short-distance
Long-distance
VLF
Very Low Frequency
Surface wave
lonospheric wave
(under 30 kHz)
LF
Low Frequency
Surface wave
lonospheric wave
(30 ,....., 300 kHz)
MF
Medium Frequency
Surface wave
lonospheric wave
(300 ,....., 3,000 kHz)
HF
High Frequency
lonospheric wave
lonospheric wave
(3,....., 30 MHz)
Table 1.
The state of the ionized layer is closely associated with the
relative positions of the sun and the earth and also with the
activity of the sun. The
D
and
E
layers almost disappear at
night. while the F layer changes in height and density depen-
ding on daytime or night time, and changes the upper fre-
quency limit to be reflected. Occasionally, "clouds" of ions
will drift through the
E
layer, causing strong signal propaga-
tion (called "sporadic
E
propagatin") over several hundred
miles. usually between
15 MHz and
30 MHz.
and
sometimes higher in frequency.
Fig.
4-1
Such a phenomenon also occurs with changes in seasons or
rotation cycle of the sun as weil as unusual activities of the
sun (change in the sunspot cycle every 11 years. unexpected
explosion on the sun. etc.). To cope with this. international
short-wave broadcast stations change their frequencies ac-
cording to seasons or directions of radio waves. or use
different frequencies at the same time for broadcasting the
same program.
Frequency Distribution in the Broadcast and Amateur
Bands.
The R-1000 receiver covers a wide frequency range extend
ing from 200 kHz to 30 MHz. to receive the internationally
determined frequencies assigned to many broadcast and
communications services.
As shown in the Frequency Allocation Chart. Fig. 4-2. broad-
cast and Amateur radio station frequencies are allocated in
specific bands expressed in megahertz (MHz) or wavelength
in meters (m). Also in Fig. 4-2. the frequencies of "other
stations" are assigned for fixed station business use. marine
mobile. aviation mobile. land mobile. radio beacon stations.
etc. The following relationship exists.between frequency and
wave length:
Wave-length (m)
=
Frequency (MHz) =
300
Frequency (MHz)
300,000
Frequency (kHz)
300
Wave length (m)
As will be seen from this relationship, the 31 m band and 9
MHz band, for exanple. are the same shortwave broadcast
band, covering the range of 9.500 kHz to 9.775 kHz.
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