Microwave and Optical QSO for the
ARRL 2008 "10 GHz and Up" contest
August 20, 2008 (UTC)

Figure 1:
  A view to the south from Inspiration point toward Nebo.  Nebo is just barely visible in the haze (in the large version) to the left of center.
Bottom:  A view to the north from Nebo toward Inspiration point.  In this contrast-enhanced image,  Inspiration point is near the first bump from the left in the distant haze.
Click on either image for a larger version.
A view
                    to the south from Inspiration point
                    to the north from Nebo
This QSO was mentioned on Page 87 of the March, 2009 QST.

The excuse:

As with last year we decided to go out into the field and throw signals at each other, using the annual ARRL "10 GHz and up" contest as an excuse to do so.  Again, we were going to do some optical ("lightbeam") communications as well as other bands.

Unlike last year, the weather wasn't particularly threatening as there wasn't any need to repeatedly take refuge from fierce, fast-moving thunderstorms!  Somewhat like last year, however, it was pretty hazy - again, due to wildfires elsewhere in the western U.S. but the density of the haze was nothing like it had been last year!  From the Nebo site, it was possible to pick out the 107-mile distant outline of Willard Peak, immediately south of Inspiration Point with the naked eye - if one knew where to look!

Contacts on "low" frequencies:

The locations chosen were the same as those used last year - and why not?  They were separated by a respectable distance (107.04 miles) and we were familiar with the locations, and we weren't trying to be original, but make a few contacts.  This time, too, since the weather was more cooperative, we decided to make time to make attempts to work on other "low frequency" bands - such as 10 and 24 GHz!

Being that this was the first weekend of a two-weekend ARRL event, there were several others out-and-about, armed with microwave gear.  While there wasn't exactly a pileup, there was about as much activity on 10 GHz this time as there ever has been around here.

Not too long after I arrived at the Nebo site, Ron, K7RJ along with his wife Elaine, N7BDZ and Robb, N0KGM arrived at Inspiration point and began to set up, with Robb documenting the event on video. A few minutes after an unsuccessful attempt by Dale, WJ7L and I to make contact, I heard a burst of off-frequency SSB.  Quickly retuning, I heard Ron's signal blasting through. Quickly re-peaking my antenna - an 18" DSS satellite dish - I called him and he came back, reporting that he was using just a 17dBi gain horn:  This wasn't too surprising, as we already knew that out path was line-of-sight!

As Ron put it:

"Utah has a small, but enthusiastic microwave presence. I operated the [evening] of August 17, 2008 [UTC] from a mountain ridge in the Utah Wasatch mountains at about 9000 ft. elevation, which is about 5000 feet above the average terrain. One contact was to an 80 km distant station (WJ7L) that used a homemade omnidirectional slot antenna from his home. He was warm in his shack while we were getting cold on the mountain about a mile higher in the air! The other 10 GHz SSB and wideband FM contacts were from distant mountain sites, ( WA7GIE and KA7OEI) We tried 24 GHz, but we still have some equipment issues."

Shortly after arriving on-site, Dale appeared on 2 meters and we had tried to make a QSO on a frequency 10 kHz below that of the WA7GIE beacon. Unfortunately, with a lot of dirt between us (mountains entirely blocked my view of the Salt Lake Valley) I heard nothing from Dale.  In the meantime, Dale and Bryan, W7CBM, managed to work each other across the valley with no great difficulty.

Figure 2:
Top Left:
  At Inspiration point, Ron, working with the 10 GHz transverter and its IF radio while Robb documents the event.
Top Right:  The 10 GHz transverter with horn antenna, looking toward the south.
Bottom Left:  The 10 GHz station at Nebo end, showing the homebrew 10 GHz transverter and the IF radio/battery.  (Yes, the transverter's components are, in fact, screwed down to a piece of plywood!)
Bottom Right:  A DSS dish and feedhorn used for the 10 GHz SSB contacts.
Click on an image for a larger version.
                    working with the 10 GHz IF radio and transverter
                    while Robb documents the event. The 10
                    gig transverter and horn antenna, ready to go!
The 10
                    GHz transverter and IF gear on the table at the Nebo
                    Satellite dish and feedhorn used on 10 GHz SSB at
Dave, WA7GIE, on a family outing, got a pass from his XYL to go into the "nearby" hills of central Utah.  Following the easy 5x9 contact, Ron continued to work Dale, still on his omni and behind a mountain from Ron's vantage point, until Dave appeared on 2 meters after a longer-than-expected delay:  His intended radio site had been occupied by a group of campers, so he went to a more-distant site along Skyline Drive, a scenic byway that threads its way along the roof of a mountain range in central Utah.  Once he'd set up his gear, he appeared on 10 GHz SSB as well:  Being only about 20 miles away and line-of-sight from me, he had an extremely strong signal - even with my antenna still pointed toward Ron, almost 180 degrees off his bearing.

Swinging my antenna toward him and peaking, we more-or-less pegged each other's FT-817's S-meters and we quickly turned our attention to having Ron and Dave try to work each other.  At about 128 miles - with mountains in the way - the first few attempts were unsuccessful until a strategy was decided:  Being very near the 11,900+ ft. Mount Nebo, I would transmit a signal on which both Dave and Ron would peak their dishes, hoping for a reflection or refraction of some sort from the Nebo mass.  This strategy worked and, despite a bit of random, deep QSB, they managed to work each other over the non line-of-sight path during the occasional, strong signal peaks.

Robb put a short video documenting Ron's 10GHz activities at Inspiration Point on YouTube:

As it was starting to get dark, we switched over to wideband 10 GHz FM.  Using the DSS dish at my end and with Ron using his 17dBi horn, we were able to work each other, verifying that our WFM gear was actually working, so we switched to 24 GHz WFM, but with no results:   Not having proven our 24 gig gear as much as we had our 10 gig gear, we weren't entirely surprised - but this left us with further work to do!

QSYing to the "Red" band:

After having made as many 10 gig contacts as we could - and now that it was getting dark - we turned our attention toward operation on the "Red" band.  In the darkness it took a few minutes to disassemble the microwave gear and configure the optical gear, but before too long, we managed to "rough-in" each other's beams and a few more minutes to "fine-tune" each end's aiming.

This year, we each used exactly the same gear as last year to complete the two-way optical QSO - see below:  Both sides used high-power (3-watt) red LEDs and large, plastic Fresnel lenses.  Even though it was quite hazy, it was much-less so than last year so we had fairly good-signals end-to-end with relatively little fading.

Audio clip:

Robb put together another short video documenting Ron's 24 GHz attempt and initial "Red-Band" activities at Inspiration Point on YouTube:
A contact using cheap laser pointers:

This year, we decided to try something that we didn't get a chance to do last year due to weather and/or time constraints:  Make the 107 mile path using cheap, standard laser pointers.  For a number of reasons lasers, using small apertures, aren't particularly well-suited for high-quality optical communications over long paths - see this page for an explanation of this phenomenon.  Somewhat fortunately, with the significant haze present, scintillation was significantly reduced, but as you can hear from the following audio clip is still very apparent:

Audio clip:

Figure 3:
The "Laser Vernier Thingie" devised and built by Ron to allow precise, repeatable Az/El adjustment of the laser pointer.
Top:  Showing the rubber-band tension springs and mounts for the laser pointer.
Bottom:  The plastic "hinges".  These hinges are very simple and have little side-play, allowing one axis to be adjusted without affecting the other.
Click on either image for a larger version.
Ron's "Laser Vernier
Ron's "Laser Vernier
At the beginning of this file can be heard a brief segment of the 1 kHz "alignment" tone, immediately followed by an exchange:  Note that Ron's audio can be heard only because of the open microphone on the optical transmitter at the Nebo end picking up and retransmitting receive audio - which means that his voice went both ways over the 107 mile laser-pointer path!

Quite apparent in this audio clip is a sort of "rumbling hiss" caused by the scintillation of the laser's light:  Measurements indicate that there is at least 40dB of scintillation present on the audio, but the redundant nature of human speech and the brevity of the most severe of these "dips" in amplitude still allow good intelligibility, albeit with rather poor audio quality.

Aiming the laser pointers - the challenge:

While the aiming of the LEDs is fairly easy, we knew from past experience that aiming even rather poorly-collimated laser pointers was a significant challenge.  After prior arduous and hair-pulling attempts in aiming lasers (and the LEDs!) an "audible S-Meter" system was devised where an audible tone was used to convey the strength of the received optical signal - modulated with a 1 kHz "alignment tone" - via pitch of the audible S-meter:  The operation is simple:  The higher the pitch, the better the signal!  This device allows much simpler aiming as it is a pitch - subtle differences of which are much more-easily discerned by the human auditory system than absolute amplitude and as such can be readily transmitted across a radio or optical link.  Additionally, the response of this tone is instantaneous:  If one is listening to the receiving end's audible S-meter - say, via a radio link - and one even briefly "flashes" the laser across the detector at the receive end, that burst of modulated light at the receiving end will be instantly heard as a "pip".  Needless to say, with such instant feedback the aiming is greatly simplified as it becomes very practical to perform a manual "scan" to determine the rough aiming!

Having a good system for alignment is one thing, but actually aligning a laser is another problem!  For this task, I simply mounted my laser pointer to the camera mount atop my 8" reflector telescope, using its polar mount and verniers to provide both a stable mount and fine-tuning.

What if you don't happen to have a stable telescope mount handy?

Past experience had shown that even with a reasonably good-quality photographic tripod, it was not practical to point with the finesse and precision required to aim even a cheap laser pointer!  The main problem with a tripod is that when one attempts move it a very small amount (fractions of degrees) it's difficult to gauge exactly how far it actually moved - which makes repeatable or proportional motions practically impossible!  To make matters worse, most tripods have a viscous grease (e.g. "fluid head") that provides smooth movement for photographic purposes, but provides unpredictable amounts of backlash when very tiny changes are attempted - especially at cold, mountaintop temperatures!

Something else had to be devised, so Ron took up the challenge.  The result can be seen in Figure 3.  This device mounts to a standard tripod, but using bolts, precise Azimuth and Elevation adjustments can be made after initial "rough aiming" with the tripod and locking it down.

This device, made in a single evening from scraps of plastic and hardware that Ron had laying around, looks crude - but it works very well:
How well did it work?  Ron reports "Very!" - and it saved quite a bit of hair-pulling and time.  One of the advantages of this sort of device is that it can, in fact, be used with a standard tripod - which is something that is small and light practical to haul on one's back to sites without vehicle access!


There is actually a web page that describes using laser pointers for long-distance optical communications in some detail, and it's called "Using Laser Pointers for Free-Space Optical Communications".

After several hours of shooting microwaves and photons at each other, we all decided that it was getting cold and late, so we threw our gear in our vehicles and headed back...

Additional details:

I'd like to thank those that helped, including:

- Ron, K7RJ.
- Elaine, N7BDZ, Ron's much better half, who took the photos at Inspiration point.
- Robb, N0KGM, documenting things at Inspiration point on Video.
Figure 4:
Top Left:  Ron, talking on the coordination frequency to set up a microwave contact while the moon rises and sun sets.
Top Right:  Moonrise at Inspiration point.
Center Left:  Ron, making adjustments to the laser transceiver.
Center Right:  Red photons from Nebo being launched toward Inspiration point.
Bottom Left:  In the distance, red photons from Inspiration point.
Bottom Right:  Illuminated by moonlight, the optical and microwave gear at Nebo.  If you look carefully, you can see the "lit up" laser pointer mounted atop the orange 8" reflector telescope.
Click on an image for a larger version.
                    setting up microwave gear in the light of the rising
                    moon. Moonrise
                    at Inspiration point
                    aligning the laser pointer for the QSO Throwing red photons toward
                    Inspiration point, from Nebo.
                    from Inspiration point, across Utah Valley The
                    optical gear, in the moonlight

At the south end of the QSO:

Present:  Clint, KA7OEI.

Location:  Along the Mt. Nebo Scenic Loop Road that goes between Payson and Birdseye, Utah.  This location is about 525 feet southwest of the one used during the August 18th, 2007 expedition.

WGS84 coordinates:  39°, 51' 16.9" North,  111°, 42' 14.7" West, Altitude was 9406' (2867 meters) according to GPS.

Grid square:  DM49du

At the north end of the QSO:

Present:  Ron, K7RJ with his wife Elaine, N7BDZ, and Robb, N0KGM

Location:  A place called "Inspiration Point" that is slightly north and west of Willard Peak, which is north of the city of North Ogden, Utah - the same place as last time

WGS84 coordinates:  41°, 23' 26.6" North, 111°, 59' 9.6" West.  I don't have Ron's GPS reading for the altitude, but according to the USGS topographical maps, the altitude is almost exactly 9400 feet (2866 meters).

Grid square:  DN41aj


The calculated distance (as a crow flies) using the Haversine method is 107.09 mi. (172.34km) using the RadioMobile program version 8.0.5.  This is about 230 feet (70 meters) farther than the August 18th expedition.

Other path statistics:
About the microwave gear:

Inspiration Point:
Mt. Nebo:
About the optical gear:

Equipment common to both sides of the QSO:

Optical gear used on the North-to-South link:

Optical gear used on the South-to-North link:

Notes about the audio clips on this page:

Final comment:  "Is it 'coherent' enough?":

Over the years, there has been some discussion as to whether or not "Lightwave" communications - not being covered directly by the same FCC rules that govern amateur radio communications - were really amateur radio communications.  This was taken up by the ARRL contest committee and is spelled out in this document:  http://www2.arrl.org/contests/announcements/rules-vhf.html.

In particular, there was section 1.12 in the General Rules for ARRL Contests above 50 MHz which stated:
1.12.  Above 300 GHz, contacts are permitted for contest credit only between licensed amateurs using coherent radiation on transmission (for example, laser) and employing at least one stage of electronic detection on receive.
Unfortunately, this statement is rather vague and could be interpreted in several ways.  At the time that this ruling was made (in mid-1980, perhaps) one of the few methods that had been historically been used for "all-electronic" lightwave communications had been via laser - but it most certainly does appear to limit the scope to only lasers.  Although I am not privy to the internal discussions behind this, it would seem that the intent was to prevent amateurs from using blinking lights to send Morse code to each other, hence the necessity for "...at least one stage of electronic detection on receive" but I would hope that there was never any intent to straightjacket experimentation in so-wording the rule.

The early portion of that statement, namely "...using coherent radiation on transmission (for example, laser)..." was a bit more mysterious.  It would seem that it was be worded to preclude the use of a tungsten light source (e.g. light bulb) from being modulated, but why, exactly did the authors feel it necessary to narrow the possibilities?  Perhaps a "light bulb" was considered to be too passé, or maybe it was considered to be too far distant from being any sort of "transmitter" in the conventional sense in that it was more of a broadband noise emitter than a device that generated a "signal" on a specific frequency.

What is interesting, though, is that there is that statement "(for example, laser)" that suggests that the means used need not be a laser, specifically.  At the "low" end of this scale, say - in the millimeter-wave range - it is unlikely that Lasers would be applicable at all.  It would, therefore, imply that the use of a laser, specifically, wasn't required!

What about the "coherent radiation" portion of the statement?  The degree of coherence isn't stated and its purpose would seem to be to remove the use of "noise" sources (e.g. incandescent light bulbs) from consideration.  At the time of writing, the mostly likely laser source available to the radio amateur was a gas laser tube, which arguably puts out a fairly coherent (single-frequency) light source and it is entirely possible that other suitable types of light sources fathomable at the time.  Since that statement was written, however, a number of other light sources have become available - including semiconductor lasers.  This, again, brings the question of "coherence" to the forefront:  Compared to a gas laser - such as a typical Helium-Neon laser tube - the spectra of a laser diode is not particularly coherent in that its energy is spread over a fairly wide range of frequencies - but it seems to be "coherent enough" for the definition.

Since the above rule was written, other distinctly "non-laser" but monochromatic devices - such as LEDs - have become available with capabilities that make it practical to use them instead of lasers for long-distance communications.  Had such high-power LEDs been available at the time of writing been available, would they have included or excluded them - and in either case, what would have been the justification for doing so?  We'll probably never know, and there's probably little reason to debate that point!

Fortunately, the ARRL does respond to changes in technology - especially if they are lobbied to do so - and on July 16, 2010 the "Rule 1.12" was changed to:
1.12.  Above 300 GHz, contacts are permitted for contest credit only between licensed amateurs using monochromatic signal sources (for example, LASER and LED) and employing at least one stage of electronic detection on receive. LASER usage is restricted to ANSI Z136 Class I, II, IIa, and IIIa (i.e., output power is less than 5mW).
This revision would seem to increase the options of light sources used for communications but clearly precluding  unfiltered "thermal" sources (such as tungsten lamps).  What is interesting is the inclusion of a 5mW limit for laser use - but this probably has to do with safety and legal issues that become increasingly important as power levels go up.

Return to the KA7OEI Optical communications Index page.

If you have questions or comments concerning the contents of this page, feel free to contact me using the information at this URL.

Keywords:  Lightbeam communications, light beam, lightbeam, laser beam, modulated light, optical communications, through-the-air optical communications, FSO communications, Free-Space Optical communications, LED communications, laser communications, LED, laser, light-emitting diode, lens, fresnel, fresnel lens, photodiode, photomultiplier, PMT, phototransistor, laser tube, laser diode, high power LED, luxeon, cree, phlatlight, lumileds, modulator, detector

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