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More Long Delayed Echoes on the EME Circuit

LONG DELAYED ECHOES ON EME CIRCUIT

Long-delayed echoes have been reported by the amateurs at high frequencies for a long time).1 2 3 More recently Hans Lohmann Rasmussen, OZ9CR, reported receiving echoes delayed an additional two seconds after his normal EME echoes at 1296 MHz were received from the moon. Hans sent me a copy of his findings and after I circulated them to Dick Turrin, W2IMU, and Bob Burns, WA2HVA, both of Bell Laboratories, and James H. Trexler of the Naval Research Laboratory, the response was unanimous that he should report this unique event in one of the scientific journals. It later appeared in Nature magazine."4 Since then he has received a letter from Alan Goodacre on behalf of the Ottawa Canada Moonbounce Group, VE3OMG, reporting echoes of one second or so delay after the moon's echoes at 144 MHz.

OZ9CR's 1296-MHz equipment consists of a 26-foot-diameter parabolic antenna with a circularly polarized feed horn and 500 watts cw from the transmitter. The receiver has a noise figure of 2 dB and a passband of 500 Hz. The transmitter had a distinctive note because of a spurious frequency near the fundamental. On the EME circuit it was very easy to identify the signal because of this unique characteristic. The following is the report Hans originally sent me.

- Howard O. Lorenzen, W3BLC, 3713 Bangor St. S. E., Washington, DC 20020.


GHOST ECHOES ON 1296 Mhz

In the middle of the summer of 1974, I had a very queer experience while working moonbounce on 1296 MHz. Now I am curious to know if any vhf or uhf amateurs have ever observed anything similar, because this was such a strange happening that I could hardly believe my own ears. Here is how it all came about.

I had been told that there was some chirp on my signal so I thought that it would be a good idea to listen to a few moon echoes before I started to work on the power supply. Then I would have something for comparison later on. It was late in the afternoon with the sun about straight west and the clear moon southwest at 30 degrees elevation. I had been drawing echoes for some time and just stood and pondered about that chirp, when out from the speaker came a second echo signal. It was a hoarse whispering signal with the true characteristics of the signal that I had just received from the moon. I was so surprised that for some time I stood stiff and listened for what would follow. But nothing more came, so I keyed a new signal and waited. In came the moon echo, and the ghost echo about two seconds later - with my transmitter chirp and everything.

Again and again I drew echoes, and apparently there was no doppler shift and certainly no beat tone on the signal. The hoarse characteristic of the echo reminded me of a sun-noise signal. My first impression was that this was a double echo from the moon, and the time elapsed could very well fit into the picture. I was aware that this was something unusual and should be recorded, but my little recorder had been dropped on the floor and was badly damaged, so I thought the next best thing would be to keep on and see what happened. For twenty minutes I kept working both echoes and this sinister signal kept coming in without any change. By and by, my neighbor's big birch tree came into the way and the signals became weaker, and when half the dish was covered I could hear no more. After this, I happened to think that for a while during the observations I had neglected to aim the dish and the moon echo came in very weak while the ghost echo came in as usual. This would suggest that the sky away from the moon could perhaps reflect a radio signal, but this possibility did not appear to me at the time and I still thought it was a double echo.

The next day we had a' regular radio blackout, which lasted several days. In the papers I lead that a violent eruption had taken place on the sun; a large sunspot had appeared and it could be seen without glasses. This at once gave me the idea that the eruption had something to do with my ghost signal. And why not? I realized that the sun three hours earlier had been very close to the position that the moon had at the time when the echoes were heard. A large streamer of gas from the corona of the sun on its way toward the earth could perhaps be highly ionized and be able to reflect a radio signal. If this streamer approached with a speed of 1000 kilometers-per-second with a front like a shock wave, it might possibly be a good radio reflector. What other mechanism could have reflected a radio signal from 800,000 kilometers out in space, in four to five seconds? Very large radar stations can draw echoes from the sun but there seem to be no records of other reflectors. This is perhaps one of those rare occasions when conditions were just fight and some happy-go-lucky radio ham happened to be present when queer things happened.

- Hans Lohmann Rasmussen, OZ9CR, Aasum, DK-5000 Odense, Denmark.


MORE GHOST ECHOES

Rasmussen's recent report of ghost echoes while conducting moonbounce tests (ref. 4) reminded me of an experience I had in the late 1960s in connection with moonbounce tests on 144 MHz. My equipment at VE3BZS/2 consisted of an array of sixteen four-element Yagi antennas fed with approximately 500 W of rf power. The receiver noise figure was about 3 dB and the bandwidth about 30 Hz. Pulses of one second duration were transmitted every 10 seconds. With the equipment parameters used, I would only occasionally receive lunar echoes.

One time while playing a tape recording of my efforts to another amateur radio operator, he remarked that he could hear a few weak echoes; I replied that I didn't hear any. Upon replaying the tape it turned out that the energy was not being received in the lunar time slot of 2.5 to 3.5 seconds, where I had expected it, but somewhat later, one second or so as 1 recall. These nonlunar echoes were too weak and transitory to document properly in the scientific literature at that time but I mention them now as there seems to be increasing evidence of long-delay echoes of nonlunar origin.

Rasmussen's observation is of considerable interest as it appears to be one of the few cases when persistent long-delay echoes have been observed and related to some physically reasonable mechanism.

- Alan Goodacre, VESAEJ, 1286 Woodside Dr., Ottawa, Ont. K2C 2G9.


1 - Dellinger, "Observations on Long-Delayed Radio Echoes," QST, August, 1934.
2 - Viilard, Graf and Lomasney, "Long-Delayed Echoes - Radio's Flying Saucer Effect," QST, May, 1971.
3 - Viilard, Fraser-Smith and Cassam, "LDEs, Hoaxes, and the Cosmic Repeater Hypothesis," QST, May, 1971.
4 - Rasmussen, "Ghost Echoes on the Earth-Moon Path," Nature, 257, 36 (1975).


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