WSPR 80m (3.5 - 3.7 MHz) band activity data recorded for a 48 hour period on the 22~23/05/2017

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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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Page last revised 05 May, 2025