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Data from the WSPR web site relating to
monitoring and transmission from VK6YSF Northam Western Australia.
WSPR
Frequency: Dial 3.5926 MHz USB (occupied bandwidth 3.5940 -
3.5942 MHz)
Grid location: OF88II
Local Time = +8:00 hours (0:00 =
8:00AM)
Transmission Power 37 dBm (5Watts)
SSN (Sun Spot Number): 20
Equipment: TS-930 at
5W, Radio computer
interface
Antenna: Multi-band
dipole with T-Match tuner and 4-1
Current Balun
Regular
short distance contacts between VK6PK and VK6YSF and a number of
other local stations had noted that the band would go dead for a
consistent hour or two on odd occasions. WSPR pings have been
monitored between VK6PK and VK6YSF for two 24 hour periods
(22/05/2017 & 23/05/2017) to see if these drop outs could be
observed.
WSPR data has been graphed using
Excel. Horizontal axis = UTC Time, Vertical axis = dB below the
noise floor.
VK6PK
Distance: 32.0km
Grid location: OF88ee
dBm: 37
The
pings shown in orange for the 23/05/2017 clearly show the pings drop
well down below the noise floor from just past 10:00UTC (18:00WST)
to just past 12:00UTC (20:00WST) a period of about two hours.
Although
not common on the 80m band I believe that our short range
communications are be affected by a brief skip zone be created due
to the weaker than usual F layer.
At
lower latitudes (Southern Hemisphere) higher latitudes (Northern
Hemisphere), a noticeable skip zone sometimes appears on the band
during darkness hours in midwinter, which can be as much as 500 km
(300 miles), rendering communication with some nearby stations
impossible. This is not generally a problem at middle or equatorial
latitudes, or for large parts of the year anywhere, but it does
occasionally limit local wintertime traffic on the 80m band in areas
such as Southern Australia, Northern Europe, the northern tier of
the United States and Canada.
To
decrease or eliminate the skip zone is by decreasing the operating frequency
(Dropping to a lower band if possible). A point is eventually reached when decreasing
the frequency results in a zero distance skip zone. In other words,
a frequency exists for which vertically incident radio waves will
always be refracted back to the Earth. This frequency is equivalent
to the ionospheric plasma frequency and is also known as the
ionospheric critical frequency.
Illustration of long distance radio
propagation with vertical incident refraction and long distance
radio propagation with skip zone.
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