Over the last few months, there have been plenty of long distance propagation paths reported on the 40 MHz band but nearly all involve at least one station in the northern hemisphere. In this post, we'll look at a recent East-West path in the southern hemisphere.
5th April 2023: Short wave listener Tony Mann in Perth, Australia reported reception of the ZS6WAB beacon in South Africa on 40.675 MHz. The distance was about 8320kms.
Tony Mann writes... "To my surprise the South African 8m beacon on 40.675 MHz, ZS6WAB, made an appearance here for over 2 hours after 0615 UTC. I am amazed it was detectable, and for so long here.
The receiver is an Icom IC-R75 with audio via usb mode. The beacon was first heard around 0615 UTC on a north facing 6m broadband dipole at 5m agl. When I rotated the dipole around to face east-west the signal was much stronger.
The signal was audible for over an hour, peaked again 0645-0655 UTC and was visible on Spectrum Lab past 0800 UTC. The decoded morse revealed the callsign ZS6WAB and grid locator KG46RB. The great circle distance is 8320 km (5200 miles)."
Tony posted this video on his YouTube channel...
Analysis... While this opening was ongoing, Tony Mann took a screenshot from the Australian Bureau of Meteorology website which shows the predicted F2 layer critical frequency. This is the frequency that is returned from the F2 layer in the ionosphere when a signal is sent straight up.
The actual maximum usable frequency (MUF) is roughly three times the critical frequency i.e. a signal at perhaps an elevation of about 5 degrees above the horizon. The map suggests a MUF of maybe 3 x 11 MHz / 12 MHz = 33-36 MHz. It's not exact but it suggests that a path in the low VHF spectrum (30-40 MHz) might be possible.
The second thing to note from the graphic above is that conditions in the ionosphere are now better in the southern hemisphere now that we have passed the equinox.
If we consider how many good east-west paths there were in the northern hemisphere in January to March then there should be similar east-west paths on the 40 MHz over the next few months from South Africa to Australia and South America and from Australia to South America.
It really is just a case of getting more people transmitting and listening.
Link... For more information on the 8m band, see my 40 MHz page.