[Ronja] [turner at ussc.com: [Laser] 173 mile optical 2-way QSO completed]
clock at twibright.com
Mon Oct 8 21:10:31 BST 2007
278.56km without a laser...
----- Forwarded message from "C. Turner" <turner at ussc.com> -----
Date: Mon, 08 Oct 2007 13:53:31 -0600
From: "C. Turner" <turner at ussc.com>
To: laser at mailman.qth.net
Subject: [Laser] 173 mile optical 2-way QSO completed
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US;
rv:184.108.40.206) Gecko/20070802 SeaMonkey/1.1.4
On the night October 3, 2007, two groups here in Utah were able to
complete an electronic 2-way optical QSO over a path that, according to
the RadioMobile program, was 278.56km (173.1 miles) in length.
The north-to-south bearing was 177.1 degrees true, with the southern end
of the path being a site on a ridge just below Swasey Peak in the House
Range, west of Delta, Utah, to the northern site in the Raft River range
in northwestern Utah, south of Standrod, Utah, just south of the Idaho
border. The elevation of both locations was just a hair under 2865
meters ASL (9400 feet.) While it was possible to drive to the north
site using 4-wheel drive and tire chains to combat mud and snow, it was
required that the party attaining the southern site hike in from the
vehicle: Their path required route-finding on rugged terrain, several
kilometers of hiking, and quite a bit of elevation gain - not to mention
a return path in darkness while fighting a fierce wind. This optical
path crosses some of the flattest land on Earth - the Utah Salt flats.
There was also zero light pollution, owing to the fact that the majority
of the path crossed over an uninhabited military reservation.
On the south end near Swasey Peak, the party was lead by Ron K7RJ with
Gordon K7HFV and Brett, N7KG. On the north end near George Peak was
Clint, KA7OEI, solo.
Air conditions on this occasion were not particularly good: Owing to
winds preceding a cold front, a fair amount of dust had been kicked into
the air, causing significant decrease in visibility, but the winds may
have helped in maximizing thermal homogeneity of the air between our two
sites, reducing the amount of scintillation: Preliminary analysis of
scintillation shows it to be much less than that experienced during
previous 15 and 107 mile experiments.
A two-way MCW exchange was completed fairly easily, followed by the
successful reception of a voice report at the south end - but it was
noted that the link margin in the north-to-south direction was a few dB
better than the south-to-north direction, making the reception
south-to-north voice report somewhat "iffy" - the voice was detectable,
but copy was extremely marginal. Also transmitted in both directions
were test tone - to provide later analysis of scintillation, and several
SSTV images were transmitted from north-to-south. All exchanges were
recorded live in a lossless .WAV format to identical digital audio
For both ends, the transmitting gear was similar, the optics based on
work done by the Australian optical group: The transceivers used
separate large Fresnel lenses for transmit and receive. On the north
end, a pair of 430x404mm lenses were used while the south end used a
pair of 318x250mm lenses. On both ends, current-modulated 3-watt red
Luxeon LEDs were used for transmit, while both receivers used a
reverse-biased BPW34 PIN photodiode with a cascode amplifier using a
saturated JFET as the input stage.
The reason for the link margin disparity between the north and south
ends is currently unknown. At least a portion of this may be attributed
to the fact that it is known that the transmitter used at the north end
has a couple dB higher optical flux output - a fact attributed to the
fact that the secondary lens was a custom-ground aspherical lens that
was designed to provide better illumination of the Fresnel lens. It is
also suspected that the receiver used on the north end may be deficient
by just a couple of dB: Even though the designs are identical, it is
possible that the difference is related to normal component variation.
During this event, at no time were the lights from the opposite ends
ever visible with the naked eye: We spent several hours trying to
acquire the signal, but just before we were about to give up, I was
finally able to spot an the extremely dim red light from the south end
using an 8" telescope: Using electronic pointing aids (e.g. an "audible
S-meter" system) we were able to acquire each others signals.
Eventually, Brett (at the south end) was able to spot the light from the
north end using a very large set of binoculars.
After our MCW, voice, and SSTV transmissions, we attempted to acquire
signals from the Lasers: Using the electronic pointing aid, this was a
trivial task during a test over a 172km (107 mile) path a month earlier
when using both the 8" reflector telescope (which was already aimed
directly at the far end, requiring only a minor tweaking of the
telescope's vernier to maximize the signal once the eyepiece was
replaced with the emitter) and again with a Laser pointer attached to
the telescope's sighting-scope mount. On this (the 10/3) occasion,
however, the Laser signal could not be acquired at the south end: A
attempt was also made to acquire a Laser signal at the north end that
was transmitted from the south end, but this, too, was unsuccessful.
It is expected that were the air conditions better (e.g. less airborne
dust) that 2-way voice communications would have been easy and that
acquisition of the Laser signals in both directions would also have been
In comparison, a 2-way optical voice and SSTV contact had been completed
over a 107 mile path exactly a month earlier, on September 3. On this
occasion, S/N of over 20 dB was noted using the exact same equipment.
Also on this occasion, experiments were done using coherent light (diode
Lasers) - both using a beam collimated using an 8" reflector telescope
and an "uncollimated" beam using just a standard $3 Laser pointer. On
this occasion, while voice communications was easily accomplished using
all three transmission methods, it was noted that the coherent light
transmissions suffered severely from scintillation, with troughs
dropping well below the measurable level - with the scintillation
experienced on the beam emitted by the 8" telescope having a notably
lower rate of scintillation with fewer instances of extreme fading. It
was also noted that the amplitude peaks of the coherent light (during
brief instances of constructive interference) were higher than those of
the noncoherent light, but that the average level was significantly lower.
At present, pictures and written accounts of the event are still being
gathered and analysis of the recordings is only in a preliminary stage.
Laser mailing list
Laser at mailman.qth.net
----- End forwarded message -----
More information about the Ronja