G4NSJ – Propagation geomagnetic storms solar wind sun spot

20/4/25. Strange 10 metre propagation:

During the last week or so, propagation on the higher HF bands, particularly 10 metres, has been affected by severe geomagnetic storms, peaking at G4. This was the reason for low maximum usable frequencies which made DX contacts on the higher HF bands very difficult, if not impossible. You can see on the WSPR Map below that most stations transmitting on 10 metres were not being heard.

For two consecutive days, no one heard my 10m WSPR signals. I thought I had a problem with the antenna. However, on the 17th April, things began to change. My signal was heard by one station, DP0GVN, down in the Antarctic.

Broadcast Bands:

I’ve noticed that the higher frequency broadcast bands have been unusually quiet recently. The 21, 19 and 16 metre bands are usually lively during the day but, not of late. Even the 31 metre band has been dead during the last 7 days.

Update 22/5/25:

The 10 metre band is worse than ever! We are just about at the sunspot maximum but you wouldn’t think so. So, what’s this all about? I’ve never looked into so-called space weather but, now I’m active daily with WSPR on 10 metres, I’ve taken an interest. I’ve started by trying to understand what the K-Index is.

The K INDEX:

The K-index is a scale used to quantify short term geomagnetic activity which is measured over three hour intervals. It ranges from 0 to 9 with higher values indicating stronger disturbances in the Earth’s magnetic field. This index is derived from data collected by ground based magnetometers located at observatories around the world. These measurements help assess the influence of space weather phenomena such as solar wind, coronal mass ejections and other solar events, on Earth’s geomagnetic environment.

A low K-index of 0 to 3 signifies quiet geomagnetic conditions, ideal for HF radio propagation. This is particularly good on the higher bands, 20 metres up to 10 metres. Under these stable conditions, signal paths remain consistent, absorption is minimal and long-distance DX contacts are more reliable.

When the K-index rises to 4 or 5 geomagnetic activity becomes unsettled. This leads to increased signal absorption and fading, especially on lower bands such as 160m and 80m.

At high K-index values, 6 to 9, geomagnetic storms can severely affect HF communications. Absorption on low bands often becomes extreme, rendering 160m and 80m virtually unusable. Polar blackouts disrupt transpolar DX routes while bands above 20m become increasingly unreliable and are plagued by deep fades and fluctuating signals.

Here’s a website showing solar conditions which is very useful.