Here is a fascinating report of such echoes from G3ZRJ. His report is different from those of many others in two unique and very interesting ways.
Tony, G3ZRJ wrote to me and said that he had heard MDEs on 1 January 2012 operating portable from Clehonger, Herefordshire, UK (IO82) between 2118-2152 UTC (= local time) on 3524 kHz. He used 90 Watts into a low-hanging homebrew Carolina Windom supported at about 7 meters at the feed point. This antenna should have a lot of high angle radiation. He worked GW3OQK in Swansea which is about 100 km away. Both of them noticed the echo. G3ZRJ had also noticed a very similar effect on 4th January 2010 during the 80M CC CW Contest.
He said that the echoes were initially so strong that he had trouble monitoring his own keying on CW. The same was noticed by GW3OQK who commented that it was difficult keying while listening to the echoes.
There are two interesting observations here in addition to the rare observation of the echo phenomenon by itself:
- There was a relatively long distance between the two stations that both heard the MDE, about 100 km. I have only heard about stations that were 20 km apart that were able to hear this effect simultanteously previously so this should indicate a very wide duct.
- The other interesting observation is the effect of the echo on their own keying. It is known in psychoacoustics that certain delays will introduce stuttering. This was just recently used to make a speech jammer by K. Kurihara and K. Tsukada in "A System Utilizing Artificial Speech Disturbance with Delayed Auditory Feedback". Here they used a delay in the 0.2 second range.
At a slightly more southern location relative to the magnetic North Pole a shorter delay is expected, so 0.2 seconds should be close. Further, the time of day and year and the frequency all match well with magnetospheric ducting.
You can listen to examples of such echoes elsewhere on this blog. Also my 2009 technical correspondence paper in QST entitled "Magnetospheric ducting as an explanation for delayed 3.5 MHz signals" will give more details about when and where these echoes occur.