Topband: Long Delayed Echo's

[Thomas F. Giella NZ4O]

>From NZ4O 160 Meter Radiowave Propagation Theory Notes at 
http://www.wcflunatall.com/nz4o5.htm

19.) Long Delayed Echo (LDE)-

A fairly common propagation mechanism by which an RF transmitted signal 
returns to the sender within 1.25-5 seconds and in rare cases of up to 30 
seconds. Research in the 1980's with HF OTHR discovered one propagation 
mechanism which involves ducting of the transmitted signal in the E-valley-F 
layer duct region of the ionosphere. A signal traveling along a magnetic 
field line much like a lightning induced whistler is another possibility.

The best time to observe an LDE is during the Fall/Spring equinox period 
when conditions are more balanced in the ionosphere. LDE's are very 
noticeable on amateur and SW broadcast signals between 17-28 mc with a peak 
near the maximum usable frequency (MUF) but occur on all bands between 
1.8-28 mc. As recently as fall 2003 I did my own brief experiments using 
Morse code (CW) on the 15 meters band. I personally observed LDE's of my own 
transmitted signal of approximately 1.5-3 seconds and I could hear a mushy 
kind of Doppler shift on my returned signal frequency.

Claims of very long delayed echo's (VLDE) on the order of hours and even 
days have been reported since the beginning of radio. Time periods of this 
magnitude would point to the "seeming possibility" of a refracting 
ionospheric type medium outside of Earth's own ionosphere, possibly 
somewhere past Pluto in the Oort Cloud. However no evidence so far has been 
found of such a medium and 99% of reported VLDE's are "probably" hoaxes.

http://heim.ifi.uio.no:80/~sverre/LDE and 
http://www.qslnet.de/member/la3za/prop

73 & GUD DX,
Thomas F. Giella, NZ4O
Lakeland, FL, USA
nz4o at tampabay.rr.com

NZ4O Daily Solar Space Weather And Geomagnetic Data Archive: 
http://www.solarcyle24.org