Long Delayed Echoes

Delay between direct signal and echo on 11. Oct 1928. Notice that several of them were observed simultaneously in Oslo, Norway and at two locations in Eindhoven, Holland.

From my pages at the University of Oslo:
Both of the lists are referred to in the Wikipedia article on the subject.

There are also several blog posts here on these echoes under the tag Long Delayed Echoes, including reports of short MDEs (medium delayed echoes/ magnetospherically ducted echoes).

The graph shown here is one of the most compelling evidences for the reality of long delayed radio echoes ever to have been produced. It convinced most skeptics at the time.

The transmitter was PCJJ in Hilversum in the Netherlands which is about 100 km from Eindhoven. The signal had a wavelength of 31.4 meters (9.55 MHz). The figure comes from Balthazar van der Pol, Short Wave Echoes and the Aurora Borealis, Letters to Editor, Nature, Dec. 1928.

Here's also an interview on Motherboard Vice: "Radio Ghosts Have Haunted the Airwaves for Nearly A Century" (October 2015).


    1. Hello Sverre, I was attracted to your site via the Elecraft reflector re macros, but now I am here I am finding more interesting stuff about echoes. I would like to give you my strange experience which happened on the T32C dxpedition to Christmas Island: I was working cw (I can't remember the freq or time of day - sorry, most things are a blur). The propagation was intermittent and the QSOs were one minute high rate then fading to nothing; however, the whole time I kept tuning across a constant drone of a signal which lasted a few seconds, then stopped, then a few seconds later would re-start. After a few times hearing this, I worked out that it was in fact someone with quite low signal strength calling me, because of the timing. I answered several times with QRZ? and the drone repeated, ie it was indeed intelligence and was answering me! It took a while for it to dawn on me that this was probably repeated echoes falling on top of each other and filling in all the blanks between characters and within characters. I told him to carry on sending, ie call again later. This went on for 3 hours while I worked other stations with lots of fading. Eventually, near the end of my shift, the continuous note broke up into distinct characters and I was able to give him a report. I wish I could remember who it was so that I could congratulate his tenacity.


      1. That's interesting to hear about. The simplest explanation could be that it has to do with round-the-world echoes, as I have analyzed here: Three paths from Japan to Norway along the grayline and here Multiple 28 MHz propagation paths and excellent conditions. Then we are talking about delays that are less than 138 ms, but other mechanisms with larger delays are also possible of course.

        It is also well known that echoes in the 0.2 sec range make speech and presumably morse code unintelligible, see the discussion in Medium Delayed Echoes.