LDE

Worked All Continents on 432 MHz was the goal during schedules I had last spring with ZE5JJ in Rhodesia. Not only did I achieve that goal, but a side benefit was observation of some long-delayed echoes on both my signals and those of ZE5JJ, which I recorded both on tape and on a chart recorder.

I usually have only a tape recorder going during EME (earth-moon-earth) work. Prior to my schedule with ZE5JJ on April 1, 1977 (not an April Fool, because I had been hearing LDEs on my signal throughout March), I ran some echo tests to be sure my system was working properly. I did hear normal (approximately 2.5-second-delayed) echoes on my signal. However, on several occasions I got two sets of echoes (2.5 and 6 seconds) and sometimes only one echo at about 6 seconds. I quickly rigged up a time reference signal to my stereo tape machine and made a strip chart recording. I did not have as much time to spend recording LDEs that night because my first interest was working ZE5JJ for my first African QSO.

Although I did complete a contact with Peter, things became rather confusing when I began hearing LDEs on his signal. When copying ZE5JJ, I was confronted with two signals sending the same data on slightly different frequencies with one slightly delayed in time from the other. To make things worse, the two signals would fade at different times and sometimes be the same strength. Needless to say, I was very confused!

ZE5JJ tells me that he heard no LDEs on his end. It is very possible that he was listening on the other side of zero beat, thus placing the LDE at zero beat or out of the passband of his receiver. Another thought (both just speculation on my part) is that LDEs are not reciprocal.

The accompanying drawing shows my set-up for recording the LDEs. The audio is routed through a narrow audio filter to enhance the signal-to-noise ratio. This also suppressed any first echo (due to different Doppler shift) I might add that my receiver is never muted. This is done to enable the pitch of the transmitted signal. to be recorded on tape for Doppler measurements.

Although I observed LDEs on and off throughout March and April, 1977, to date no other station has reported a single LDE during those two months. However, I was spending a considerable mount of time specifically looking for LDEs. It is possible to miss LDEs entirely because of circumstances I described in reference to ZE5JJ not hearing any. I have heard no LDEs since the middle of April, 1977. -- John Yurek, K3PGP

K3PGP used this setup to graphically and aurally record 432-Mhz long-delayed echoes during March and April, 1977

K3PGP's strip-chart recording of 432-Mhz, long-delayed echoes, April 1, 1977

Note: This chart is read from Right to Left !

-- And a Reply

To K3PGP: We scaled the time delay from your strip chart at 5.75 +0.1 seconds. Since the delay for two round trips to the moon at maximum distance (406,700 kin) is 5.43 seconds, we feel the echo you recorded was not likely a double moon echo. Our computer says that for April 1, 1977, at 2320Z the one-way, 432-MHz Doppler shift was +533 Hz and the one-way time delay predicted is 1.229767 seconds for a two-way round trip value of 2132 Hz and 4.92 seconds respectively. The calculations are based on data in the American Ephemeris and Nautical Almanac and included the changing relative distance between the earth and moon as well as effects of the rotating earth.

We are thus at a loss to explain your "twice delayed moon echoes" based on any known geophysical phenomena. There remain, of course, the cosmic and earth-based repeater hypotheses [February 1978 QST- Ed.]. By the way, the fact that the first set of echoes can disappear should not be taken as necessarily difficult to explain. As you know, lunar echoes fade a great deal in any event, owing to the roughness of the lunar surface and, at least at the lower frequencies, polarization on rotation in the ionosphere. So it does seem that it would be entirely possible for the first echo to be momentarily wiped out, while the second echo (which would very likely follow a different path) might be strongly audible. We think it would be a good idea to publish your observations and see if any of the amateur fraternity can come up with answers or similar observations.

Victor R. Frank, K6FV, James M. Lomasney, WA6NIL and Oswald G. Viilard, Jr., W6QYT, Stanford Research Institute, Menlo Park, CA 94025