GW4ALG's Propagation Pages

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My name is Steve Rawlings, holder of the amateur radio callsign 'GW4ALG'.  

This web page has been set up to consider a single topic, this being:

Is Ionospheric Propagation In Decline?

All the responses received so far support the view that the ionosphere is not as effective at propagating HF signals as it used to be.  The effectiveness would appear to have declined between the period 1930 and 1970, and  between 1970 and the present day.  However, I have not discovered any quantitative data to support these reported changes.

Come back often to see how things are developing . . . .

Is Ionospheric Propagation In Decline?

In October 2001, a small group of LF experimenters met at the HF Convention held at Old Windsor, Berkshire. This group of old timers comprised: Bill G0AKY; John G3BDQ; Colin G3KMP; Dave G3YMC; and myself. At some point, the conversation digressed from 73 and 136 kHz topics to our memories of HF band conditions when we were first licensed. There was general agreement that HF radio propagation appears to have been in decline over recent decades, and a number of possible causes were discussed.

Since that meeting, I have taken the opportunity to discuss this matter with other old timers. I was interested to discover that all those asked supported the view that the ionospheric mirror is not as effective as it used to be. This view is shared by Ron G6RO, and Vic G8IK - both having personal experience of low power HF operation dating back to the 1930s. Vic has given the matter some thought, and wonders whether a decline in HF radio propagation might be related to long-term changes in the Earth's magnetic field.

I am interested in hearing from others who have a definite view as to whether HF ionospheric propagation has, or has not, been subject to long term decline over several decades, with brief supporting remarks. I am especially interested in hearing from those having access to relevant signal measurement data.

I propose to summarise the responses received, and post the results on this web page.

My email address is:




Last September, British scientists announced that the ionosphere, the upper layer of Earth's atmosphere, has actually dropped! Located about 90 kilometers (56 miles) above the planet's surface and reaching up to 500 km (310 mi), the ionosphere has fallen by 8 km (4.8 mi) in the last 38 years. The culprit, according to scientists from the British Antarctic Survey (BAS): global warming.

Fossil fuels like coal and oil belch carbon dioxide into the atmosphere as they burn and trap heat in Earth's lower atmosphere. Result: the cooling of the ionosphere, so that atmospheric pressure (pressure caused by the weight of air) decreases. The ionosphere then contracts and drops in altitude. "It's another indication that humans may be changing the very environment . which supports us, even out to the edge of space," claims Martin Jarvis, the BAS lead researcher.

To measure the ionosphere's height, researchers in the Falkland Islands and Antarctica beamed radio waves up 250 km (150 mi) into the atmosphere. Ultraviolet rays from the sun remove or add electrons (negatively charged particles) to atoms in the ionosphere --a process called ionization. Ionized atoms cause radio waves to bounce back to Earth's surface. By measuring the time it takes radio signals to rebound to Earth, researchers were able to track changes in the ionosphere's height.

The sinking ionosphere shouldn't harm life on Earth, says Jarvis, and the ionosphere could bounce back up if humans stop pumping greenhouse gases into the atmosphere. At the moment, that's a big if. Maybe Chicken Little has the answer.

COPYRIGHT 1999 Scholastic, Inc.








Graph of annual sunspot numbers 1700 - 1995

HAARP facility: Index of Information About the Ionosphere + loads of links

Solar data from NGDC


Steve Rawlings, GW4ALG
9th February 2005


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