It is common indeed. An HF over-the-horizon (OTH) radar guy would call
it "backscatter" and that is exactly what the Russian (or I should say
Soviet, I guess) "woodpecker" HF signals of the 70s and 80s were,
watching us from over there, that made us all a bit crazy.
I never worked on backscatter systems, but was involved with a large
USAF bistatic "forward scatter" OHD system in the early 70s. It could do
a good job detecting certain Central Asian events until it was made
obsolete by satellite observation.
Interestingly another application of forward scatter HF OTH that has
been verified but not, to my knowledge, used is Tusnami forecasting. An
HF path, from say WWV to KH6, would show a doppler shift if the ocean
floor raised (lifting the atmosphere and hence the ionospher ever so
slightly). This is just what our HF OTH setup was very good at
detecting. Not sure exactly why that never took off. A bit off topic I
guess <g>.
73 and Happy New Year,
Joel Hallas, W1ZR
ROBERT CARROLL wrote:
>Martin-
>
>Echoes are fairly common. I ran into them on 17cw last week. When I
>finished a word etc I still heard about a dash worth of myself. It was a
>little disconcerting.
>
>Bob W2WG
>
>-----Original Message-----
>From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
>On Behalf Of Martin, AA6E
>Sent: Monday, January 02, 2006 1:21 PM
>To: tentec@contesting.com
>Subject: [TenTec] Radio Science + QSK = Radar
>
>When operating QSK at 15-20 wpm, I am running into echoes of my
>transmissions. These occur on certain azimuth bearings at certain
>times of day, most often to the SE, which is over water until hitting
>S. Africa or Antarctica from here. I've seen this from 20 M to 15 M,
>at least.
>
>Rarely, I think I've seen long-path echoes that come back to me from
>the opposite azimuth. (The SteppIR bidirectional mode picks them up.)
>More often, the return bearing is the same as transmitting. I haven't
>been able to measure the delay time accurately, but it is roughly 2
>dit (element) times at 25 wpm (about 50 msec), indicating a 10,000
>mile roundtrip.
>
>It seems to be a real effect. I can get rid of it by changing azimuth
>or using a dummy load.
>
>My question is whether other ops see this and whether it has been
>written up anywhere in "ham space". These are not the "long delay
>echoes" that people have claimed to see. The radio science community
>does run HF radar to study fluctuations in the ionosphere, and this
>phenomenon is probably well known to them.
>
>The Orion makes a fair radar set, as it turns out.
>
>73 Martin AA6E
>--
>martin.ewing@gmail.com
>http://blog.aa6e.net
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