[Laser] Lunar Eclipse #3

[Tim Toast]

Hi all
The lunar eclipse is coming up fast... 

 Wednesday evening Feb 20th in the US or Feb 21 in the
early morning hours for people in western Europe. I hope
all who can will turn their receiver-scopes toward the moon
and listen for the 120/360 Hz or 100/300Hz signals from
across the pond. If possible make recordings in .wav
format. This time it looks like both sides should have an
equal chance to hear the streetlight buzzes. 
http://www.aladal.net/toast/eclipse.html#feb21

When Yves, F1AVY heard the US 120 Hz signal last year, only
a narrow strip of the US east coast was visible to him via
the moon. This time the whole US will be visible as will
most of western Europe.

Since i have a rather noisey sound card and some local
interference here, i thought - just for fun - i would try
to transmit something during the darkest parts of the
eclipse -  from about 3:00 UT to 3:51 UT (feb 21) 9 to
9:51pm CST feb 20th. 
I will be blasting away with my xenon strobe transmitter on
7.126 Hz and 7.629 Hz (DFCW). The strobe will have a
1-wattsecond energy (1 joule) with a pulse width somewhere
between 100 and 1000 microseconds - for a peak power of
1000 to 10,000 watts. At 7 Hz pulse rates, average power
will be about 7 watts. This is a modified camera strobe
tube about 3 x 10mm in size, used with an F1.5 lens of
330mm focal length. 
http://www.aladal.net/toast/optics.html
It has a beam width of about 0.5 x 1.5 degrees. Just right
for illuminating the whole moon with the narrow vertical
and about three moonwidths in the long horizontal
dimension. I am using a two crystal TTL oscillator with a
CMOS divider chain to generate the two frequencies for
triggering the strobe. see image:
http://www.aladal.net/toast/lexse.jpg

Robert Laszlo, OM1LD has volunteered to listen with a very
sensitive PMT which will be used with a filter for 400 -
480nm in the blue. The peak continuum and lines in the blue
parts of the xenon spectrum are in that range, so those are
the best wavelengths i assume for his PMT tube. 
Xenon has even stronger lines in the NIR between 800 and
1000nm making for the best responce from ordinary silicon
photodiodes or APD's. The highest signal to noise may be in
the blue though since most of the interfering light during
the eclipse is reddish.
I choose the 7 Hz frequency based on Yves' experiments with
a variable rate strobe some time ago. It appeared there was
a 'sweet spot' or shoulder of around 7 Hz where higher
pulse rates had lower amplitudes. So that's really two
'sweet spots' - the natural responce of silicon photodiodes
in the NIR to xenon's peak lines and the special 'odd'
effect of low frequencies with the K3PGP receivers. 
Not that any of that is enough for my signal to be heard by
anyone, but i do not know it will not work (yet). I figure
though about half the power my strobe tube generates will
be captured by my lens and sent moonward. I would have to
have a fresnel with a faster F ratio to get much more out
of it.

I don't have a call sign but i will send a DFCW600? signal
on 7.629 Hz and 7.126 Hz (0.503 Hz shift).
Starting at 3:00 UT on 7.629 Hz, I will transmit for 10
minutes then switch to 7.126 for 10 minutes then back again
etc... so it will look like a 50/50 square-wave test
pattern.

3ut-------_______-------_______-------_______4ut

...so there is time for about 5 frequency steps over the 51
minutes of eclipse totality. I hope that is long enough on
one frequency to be detected :) I could be better off just
transmitting an unmodulated carrier on one of the
frequencies.

so good luck and happy eclipse watching!

http://www.aladal.net/toast/moon.html

(TST = toast)
-___-



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