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Late last week I received an interesting e-mail from Thomas Pell in Winter Haven, Florida.
It seems that Tom has been doing some building after reading my series of blogs about my lightwave adventures and has started his own adventure. As he told me initially:



"... I'm retired with too much time on my hands, and I'm tired of the big gritty hobby projects ... after reading about Harvard U's optical SETI project, which looks for extraterrestrial laser signals with a 48 inch, then 72 inch mirror. I thought it would be fun to build a setup like theirs, but at audio frequencies instead of the RF laser signals ... my purpose was to get light signals from other amateur laser dx experimenters or even ET ... better than watching my wife's TV shows. Also a giant telescope that costs almost nothing is fun too."

Tom built up the PIN diode detector shown in my notes, which was a slight variation of the one developed by Roger, G3XBM (see his great lightwave notes here) and based on an earlier plan by K3PGP.

Along with the receiver, Tom built a substantial optical antenna ... a 48" Mylar-based parabolic mirror!

"... it is a wood structure ... round piece of 1/2 inch plywood, 48" in diameter ... around the perimeter a 4" wide strip of 1/8" plywood is wrapped and glued with epoxy putty. On the upper end of 1/8 ply is another circular plywood flange inside. This flange is to glue mylar sheet. The mylar is then tensioned with tape on the side. It is something like a round guitar in appearance... a box ... you suck the air out ... I use a shop vacuum with 1/4 in rubber tube taped to vacuum hose ... hose barb epoxied to hole inside of mirror ... not ideal but if you seal it up well with epoxy, it works..."

courtesy: Thomas Pell

"At 48 inches, this is second largest mirror in eastern US ... second to the Harvard SETI 72 inch mirror experiment. The film mirror was developed by Dr. Waddell, University of Strathclyde, Scotland. It works very well for this purpose, but I don't have the proper mount yet. Very similar setup to the Harvard setup but they are only looking for nano pulse signals ..."

It seems that there is now an active movement amongst some SETI enthusiasts to search for optical beacons rather than radio beacons. When you think about it, it would seem to make just as much sense, if not more, to beacon with a modulated optical signal than with a radio signal ... and the optical signal might be far easier to detect. Some of the papers suggest that an optimum frequency would be in the near IR or deep red part of the spectrum, right where most optical amateur two-way work is presently being done.

During his first few tests of the new mirror, Thomas stumbled upon one signal (the only one) which came from just one single point in the sky ... almost directly overhead in Orion.

"At 9:30 pm 3/5/2015, using the amplifier circuit you use in your optical communication receiver connected to a 48 inch parabolic mirror, I received an apparently modulated optical signal originating in center of Orion constellation. Signal was audio frequency low to high pitch and lasted for more than an hour. I located the signal by moving the mirror back and forth across the sky for nearly an hour until I found a "blip", then focused the mirror exactly on the spot to listen to it, incredible experience."

"Received signal again last night from same location. I am becoming convinced it is information of some kind.Very irregular rapidly pulsed. This was only a test of amplifier ... I never expected this result, was totally unprepared. Meanwhile time is passing and I can't seem to contact anyone to have it confirmed before it disappears from the sky. It seems, no one has a setup like this ... this signal is either very important or it's nothing ... I think. Will let you know about outcome."

At this point, Tom is just trying to figure out what type of signal he has been hearing and will be attempting to get a better recording of it over the next few nights. I have heard his initial recording, just done with an I-pad held close to the amplifier's speaker output and it does sound suspiciously like a data train of clicking pulses. Hopefully Tom will solve the mystery soon!