Figure 1:
  A YouTube video with a clip of the setup at Bob's house along with sounds and pictures from the communications itself.

On February 2 and 3, 2008, Chris Long, VK3AML, and I had the opportunity to drive (from Utah) to Yucca Valley to visit Bob Legg, W6QYY.  Chris, who was visiting the U.S. from his home in Australia wanted to take this opportunity to visit one of the people involved in the May, 1963 long-distance optical transmission, "Project Red Line."

After a long drive, having left Salt Lake in the morning of the 1st, we arrived in Barstow where we stayed at a local motel.  The next morning, we completed the last 1.5-2 hour leg of the journey to Yucca Valley where we met Bob and Beverly who were very gracious hosts.  After arrival, we spent hours talking about the details of the 1963 event in addition to doing high-resolution scans of the extant slides and photographs, and Bob also related other details about his past work experiences with EOS and NASA, to name just a few.  In the car, I'd also brought along two optical transceivers and the associated electronics to show Bob what we'd used to do our more-recent long-distance optical transmissions.

Before Chris and I'd realized, it was getting fairly late and we'd not completed scanning of the photographs, so we took Bob and Beverly up on their kind offer to board us for the night and with this taken care of, we then had the rest of the evening without having to worry about securing lodging.  As it was starting to get dark, it occurred to me that not only did we now have the time, but we also had the necessary equipment to do an across-the-valley optical QSO.  Looking out his back door, I could see a mountain in the distance, to the southeast, topped with a radio site.  Bob, knowing the area, offered to drive out there to a vantage point along the road partway up the mountain that had line-of-sight with his house.

Setting up:


As dusk was approaching Chris and I walked out into the desert in Bob's back yard and looked around.  After a brief survey of the landscape, we quickly set up one end of the path on a rocky outcropping in Bob's back yard where Chris and Beverly would operate.

After setting up one end, we hurriedly threw gear in Bob's car and took off for the distant end, 10-12 miles driving distance, but about 7.3 miles as a crow files, maintaining communications with Chris and Beverly on 2 meter simplex.  After several minutes of driving back and forth along the road to find a good vantage point we finally parked just as it was getting dark enough to commence the communications.

Figure 2:
Top Left:  Clint, with the optical transceiver that was used on the mountain.
Top Right:  A close-up view of the transmit module.
Bottom Left:  The setup in the back of Bob's car.  The optical transceiver used at this end is described here.
Bottom Right:  Bob, looking at the very bright red light from the far end, from across the valley at about the time of initial signal acquisition.
Click on either image for a larger version.

After a few minutes of waving flashlights and laser pointers about, we had spotted each others' locations and began to set up the optical transceivers - both using high-power LEDs for transmitting, photodiodes for detection, and Fresnel-lens optics.  It took only moments before Bob and I saw the extremely bright, red light from Chris's end and before too long I was able to aim and peak on Chris's signal with my transceiver.

Over this short distance, the lights (using high-power LEDs) from each others' ends were extremely bright - so bright that with Chris, running full power at his end, caused my receiver to become somewhat overloaded:  This resulted in Chris's voice sounding somewhat tinny and slightly distorted and with a bit of intermodulation distortion (intermod) from the pilot carrier, as can be heard on the recordings.  At about this point, I realized that I'd forgotten to bring a headset/microphone:  Fortunately, I'd constructed the transmitter to have its own built-in microphone which, while usable, sounds somewhat muffled as compared to a "real" microphone - but at least we didn't need to make a quick return trip back to Bob's house to retrieve one!

Audio clip - Initial acquisition of signals:

• This segment was the first bit of 2-way voice transmitted via the link.  A brief segment of the alignment tones may be heard at the very beginning.
• This recording is a stereo composite of the recordings made at each end of the link:  The left channel contains audio received at Bob and Clint's location and the right channel contains audio received and heard by Beverly and Chris in Bob's back yard.
• Audio clip:  (MP3, 0:41, 322kB)

In this recording one can hear the somewhat muffled audio from my end (right channel) and the slightly tinny audio from Chris (left channel) caused by the receiver overload.

Over the next several minutes we experimented a bit with pointing of both ends and increasing/decreasing the transmitter power on my end, with my finally settling on a much reduced output power.  Almost from the beginning there seemed to be a problem:  Chris was reporting that my audio was extremely distorted and somewhat difficult to understand.  Assuming that it was a problem with the internal microphone or some sort of adjustment, I tried several things - such as changing the audio level and transmit power - but nothing really seemed to help, although the problem either seemed to be less-severe over time, or they simply got used to it. 

Note:

• After I got back home, I checked the recordings and found that they sounded fine.  Further investigation revealed that the speaker in the receive audio interface that Chris had been using was suffering from severe cone rub, so I replaced it.

Figure 3:
Left:  Wide-angle time-exposure across Yucca Valley.  In the center can be seen the light from Bob's house.  In the foreground from the right can be seen illumination of the foliage by the light as well as the beam being cast across the valley.
Right:  A close-up time-exposure of the beam light from Bob's house.  One can not only see the scattered beam coming from the right side of the picture, but nearby power lines that were being illuminated by our light.

I had also brought with me the low-power, modified red laser pointer (one that had originally cost $3 or so) that I'd used in previous testing and we decided to try to span Yucca Valley with that.  This, as in the case of the 1963 testing, provided to be challenging to aim - although for a different reason:  All that I had onhand to mount the laser was a photographic/video tripod.  While this fairly heavy-duty tripod is excellent for holding a camera steady, using it to precisely aim even a cheap laser pointer is frustrating for one main reason:  The viscous fluid head.  The viscous fluid caused a frustrating amount of backlash - particularly when adjusting elevation:  The signal would be easily peaked, but as soon as one tried to tighten anything or took one's hand off the handle, it would drift a tiny amount - enough to disappear from view at the far end.

Using the "audible S-meter" we soon had a weak, but stable, laser signal pointed toward Chris - but there was a catch:  Even though they could hear my audio, they could see nothing of the laser from my end after the fluid head had finished its drifting:  Here is a recording from that portion of the experiment:

Audio clip - Reception of the "invisible" laser signal:

• This segment contains the first bit of audio passed along the link via  laser.  In the beginning, a brief segment of the alignment tones and "audible S-meter" may be heard at the very beginning.
• This recording is a stereo composite of the recordings made at each end of the link:  The left channel contains audio received at Bob and Clint's location and the right channel contains audio received and heard by Beverly and Chris in Bob's back yard.
• At the beginning we hear, in the left channel, the "audible S-meter" transmitted from Chris' end and, in the right channel, the 1 kHz audio tone transmitted from Bob and Clint's end used for peaking the signal.
• The "weak" invisible signal received at Bob's house (right channel) is buried somewhat in the noise:  Headphones are recommended when listening.
  
• Audio clip:  (MP3, 2:09, 999kB)

After several minutes of communicating via the "invisible" laser beam, I decided to try to peak it again.  After spending a few more frustrating minutes trying to peak the laser and get it to stay on-point, I had some inspiration:  I set my flashlight on the laser pointer's mount and used it to "bias" against the fluid head's tenancy to make the laser drift slightly upwards.  While I wasn't able to maintain a good enough point to get a good, bright light that Chris and Beverly had seen while I was trying to aim it, it was close enough that they could see the laser with the naked eye - which meant that signals were also much stronger.

At this point, I decided to demonstrate to Bob and Chris the "scintillation compensator" circuit.  With the high-power LED and large Fresnel lenses that had been used earlier, there was no discernible scintillation (flickering) of the light across the 7+ mile path.  Using the laser pointer - with its small beam diameter and coherent light, scintillation was now clearly audible (some evidence of this scintillation can be heard in the recording above as a "wavering" in the loudness of the tone heard during the middle of the recording.)

Figure 4:
Left:  Beverly talking to Bob via the light beam.  The optical transceiver used at Chris and Beverly's end is described here.
Right:  Clint, trying to adjust the laser pointer.

Audio clip - After re-peaking the laser:

• This segment contains audio recorded just after the laser was re-peaked.
• This is a mono recording, mixing the audio received at both sites together.  This mixing caused a slight "hollow" sound to Chris' voice.
• If you listen carefully, you can hear a "fluttering" of the background hiss:  This is caused by the scintillation compensator's changing the audio gain to counteract the scintillation with the side-effect of making the background noise vary in its loudness.
• During this recording, you hear mention of "big and small rocks" along with Bob laughing in the background.  This is a reference to the aiming of the laser in the 1963 EOS experiment, where large and small rocks were used to tap the metal channel in which the laser was mounted to steer it in larger and smaller increments.
• Audio clip:  (MP3, 2:13, 1.02MB)
  

After spending a bit more than an hour, we decided that not only was the temperature dropping, but that it was also getting hungry out, so we went back to the LED communicators and wrapped things up:

Audio clip - Concluding remarks:

• This segment contains audio recorded after switching back to the high-power LED transmitter.
• This recording is a stereo composite of the recordings made at each end of the link:  The left channel contains audio received at Bob and Clint's location and the right channel contains audio received and heard by Beverly and Chris in Bob's back yard.
• In the right channel, both operators (Clint and Bob) were a ways "off-mic" which is why it sounds like we were talking loudly (we were!)
  
• In this recording, there is some evidence of receiver overload as noted by the presence of intermod in the speech as it was mixing with the 4 kHz pilot carrier - particularly in the right channel.
  
• Audio clip:  (MP3, 1:02, 486kB)

After stashing our gear, we went back to Bob's house, regrouped, and then enjoyed a very nice meal at a local Italian restaurant.


Additional pictures:

Figure 5:
Left:  Bob, just as we were concluding the evening's experiments.
Right:  The participants.  L-R:  Clint, Chris, Bob, Beverly (and Carlos, the watchdog.)

Comments, corrections, or questions?  Send an email.

Go  to the Operation Red Line page or Go to the "Modulated Light" page.