From majordomo-owner@berlioz.nsc.com Mon Mar 3 15:54:05 1997 Date: Mon, 3 Mar 97 15:54:05 PST To: jmoss From: majordomo@berlioz.nsc.com Subject: Majordomo file: list 'laser' file 'laser.9609' Reply-To: majordomo@berlioz.nsc.com Content-Length: 12696 -- >From owner-laser Sun Sep 1 20:47:33 1996 Return-Path: Received: by berlioz.nsc.com (4.1/SMI-4.1) id AA27667; Sun, 1 Sep 96 20:47:33 PDT Comments: Authenticated sender is From: "Wayne Cronin" To: laser@berlioz.nsc.com Date: Sun, 1 Sep 1996 20:41:22 -0700 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Subject: misc. questions Priority: normal X-Mailer: Pegasus Mail for Win32 (v2.42a) Message-Id: <19960902034120.AAA3831@Bravo> Sender: owner-laser@berlioz.nsc.com Precedence: bulk Well, the list has been quiet lately, so how about a few questions from a "lurker" who is absolutely a novice when it comes to lasers? First off, let me introduce myself. My name is Wayne, and my call is WA5VIF. I'm not active on the "laser bands" yet, but the subject is facinating. So, the questions: 1) Optical filtering. How is it done, or IS it done, in laser communication? I'm familiar with the optical filters used in photography. Is it the same with with lasers? What kind of "bandwidth" is possible? With the types of filtering used (or NOT used), is the difference between the 650 and 670nM diodes really important? 2) Aiming systems. What is used? How do you get a "starting position" (place to aim at)? Are GPS units helpful? 3) Modulation. What types of modulation are used, and how are they produced? Is there such a thing as AM for lasers (I'm guessing that there is NOT)? FM and PM? What kinds of bandwidth are achievable (by amateurs, anyway)? 4) Books. Can somebody reccomend a good book on lasers that is not too heavy on math and obscure theory? I'd like to learn the basics first! 5) Real-Life Examples. I know that there are commercial laser systems that support fairly wideband data over distances of up to a few miles. What types of lasers and modulation schemes do these systems use? Have such things turned up in surplus? 6) "Cloud-Bounce". Years ago, I read something (don't remember where) about some folks in L.A. who had set up a private comm system using lasers bounced off clouds. This sounds unlikely to me. Is such a system at all feasible? Well, thanks in advance for any responses! ---- Wayne Cronin wmc@worldnet.att.net >From owner-laser Tue Sep 3 09:59:17 1996 Return-Path: Received: by berlioz.nsc.com (4.1/SMI-4.1) id AA11097; Tue, 3 Sep 96 09:59:17 PDT Date: Tue, 3 Sep 96 09:53:13 PDT From: jmoss (Jim Moss) Message-Id: <9609031653.AA10976@berlioz.nsc.com> To: wmc@postoffice.worldnet.att.net Subject: Re: misc. questions Cc: laser Sender: owner-laser@berlioz.nsc.com Precedence: bulk Hello Wayne, I'll take a shot at answering a few of the questions, perhaps others can add in additional comments. See embedded comments. Jim WB9AJZ > From: "Wayne Cronin" > To: laser@berlioz.nsc.com > Date: Sun, 1 Sep 1996 20:41:22 -0700 > > First off, let me introduce myself. My name is Wayne, and my call is > WA5VIF. I'm not active on the "laser bands" yet, but the subject is > facinating. > > So, the questions: > > 1) Optical filtering. How is it done, or IS it done, in laser > communication? I'm familiar with the optical filters used in > photography. Is it the same with with lasers? What kind of > "bandwidth" is possible? With the types of filtering used (or > NOT used), is the difference between the 650 and 670nM diodes > really important? So far here in the SF Bay area, none of us are using filters. But we decided to standardize on 670nM in case we decide to do so. Edmund Scientific sells filters that are 10nM wide, so better to stick with a single wavelength. Also the price of 670's is lower than the 650's because most pointers are for eye use, so the 650 is brighter, hence more desirable. This also results in getting higher power for 670's(4-5mW) vs 650's (2-3mW typ) . This gives us an advantage as the Si detectors are typically most sensitive around 780nM. You can use photography filters or even cheepo IR filters (red plastic). I have, up to now, not investigated BW. But am planning to shortly. Have plans to build up laser/detector head for replacement on IRDA compliant computer link, 115KBPS and 1MBPS. Will try a pulse generator first just to see system response. My current rx's are set up for LF audio (1KHz). > > 2) Aiming systems. What is used? How do you get a "starting > position" (place to aim at)? Are GPS units helpful? First we use maps and familiarity with geographic features to get our EYES into the right area. Then, Typically use EYES to see a bright light (IE.. radio tower or headlights or handheld flashlight/beacon). Then use telescopes with lasers attached to hit target after "twiddling and bouncing around". With lower power lasers and good range we look at the laser source itself and tweek it in via UHF comm link back to the TX station. (we talk him in once we can see the beam). GPS will be useful at longer range, but at 20 miles the beam is narrower than the GPS accuracy. > > 3) Modulation. What types of modulation are used, and how are they > produced? Is there such a thing as AM for lasers (I'm guessing > that there is NOT)? FM and PM? What kinds of bandwidth are > achievable (by amateurs, anyway)? Here in the SF Bay Area we are using 700-800Hz modulation on-off keyed to create morse code. This allows use of DSP units on RX if needed. Have experimented with PWM on top of 44KHZ carrier, but had severe distortion at 1 mile, needs more experimentation. Art (W6RXQ) is going to try some work with Zero Cross Modulation. AM and FM can be done, but I guess that PCM will be best at some point? > > 4) Books. Can somebody reccomend a good book on lasers that is not > too heavy on math and obscure theory? I'd like to learn the > basics first! General info about lasers try author JEFF HECHT. > > 5) Real-Life Examples. I know that there are commercial laser > systems that support fairly wideband data over distances of up > to a few miles. What types of lasers and modulation schemes do > these systems use? Have such things turned up in surplus? Look up LACE on the internet searchers. or checkout: wchat.on.ca/ainsworth/lace.htm www.lasercomm.com/lasercomm www.halcyon.com/routers/campus_lan/wireless.htm itri.loyola.edu/satcom/ct_s4.htm www.spie.org/web/oer/april/lasercomm.html www.vast.unsw.edu.au/~stuartb/pvpub.html I'm sure there's more, but these are some I've used for general input. Haven't seen any in surplus yet. But tubes and diodes, pindiodes and stuff do show up. Fiber stuff starting to show up more and more. > > 6) "Cloud-Bounce". Years ago, I read something (don't remember > where) about some folks in L.A. who had set up a private comm > system using lasers bounced off clouds. This sounds unlikely to > me. Is such a system at all feasible? My opinion, not with low power. Scattering on clouds at 670 doesn't seem likely. I'm sure my RX system could detect a standard light BEACON on a cloud though. Walt (AJ6T) and I have tracked the strobes on aircraft with RX's, and can pick out strobes down in the valley from hilltops, even when surrounded by other lights. The key there is the pulsation vs the ambient level. > > > Well, thanks in advance for any responses! > ---- > Wayne Cronin > wmc@worldnet.att.net > Jim WB9AJZ/6 Sunnyvale, CA >From owner-laser Thu Sep 12 09:57:36 1996 Return-Path: Received: by berlioz.nsc.com (4.1/SMI-4.1) id AA12647; Thu, 12 Sep 96 09:57:36 PDT Date: Thu, 12 Sep 96 09:57:33 PDT From: jmoss (Jim Moss) Message-Id: <9609121657.AA12637@berlioz.nsc.com> To: laser Subject: Who's gonna be on this weekend? Sender: owner-laser@berlioz.nsc.com Precedence: bulk Walt (AJ6T) and I (WB9AJZ) will be active on laser Saturday night here in the SF Bay area. Anyone else want to play? Contacts count for the September VHF contest if gridsquares are exchanged. We are still deciding on where to go for this one. Jim WB9AJZ/6 CM87xi >From owner-laser Mon Sep 16 09:08:18 1996 Return-Path: Received: by berlioz.nsc.com (4.1/SMI-4.1) id AA06083; Mon, 16 Sep 96 09:08:18 PDT Date: Mon, 16 Sep 96 09:08:14 PDT From: jmoss (Jim Moss) Message-Id: <9609161608.AA06064@berlioz.nsc.com> To: laser Subject: Laser notes 9/16 Sender: owner-laser@berlioz.nsc.com Precedence: bulk Guys, Walt (AJ6T) and I had another successfull Q on laser during the contest, about 15-20 miles (Don't know his exact location for calculation). I found him in about 3-5 minutes using a 500mm scope, no crosshairs. Once I got close, I just tweeked the 4-40 screws I use on a 2' "beam" for x and y adjustment. He has a similar setup, but didn't set up for the paralax adjustment. This is critical and seems an easy step to forget. I am using screws with my fingers currently to adjust. As long as the tripod to jig mount is stable, I don't seem to have problems, but the 2' length causes a bit of wiggle when adjusting. I think that can be minimized by moving the adjustment screws so they are centered over the tripod, thus reducing the moment. I also paced off the width of Walt's diode laser beam. 21 steps = 63ft wide. So depending on my distance (I did some rough guessing) the divergence is just about 1 mR. Also tried 2 other RX units. One worked fine with the 8" mirror. The other I could not align, as it has a very very small active area, and we were rushed to get back to the contest (and our kids were getting over active!). My main RX unit with a large PIN diode about .25"x.25" could actually very weakly, hear the signal with NO LENSES! Guess I should calculate the path loss and divergence and figure the sensitivity. Jim WB9AJZ CM87xi Sunnyvale, CA PS Art (KY1K) thanks for the note! Jim >From owner-laser Mon Sep 16 21:43:34 1996 Return-Path: Received: by berlioz.nsc.com (4.1/SMI-4.1) id AA28234; Mon, 16 Sep 96 21:43:34 PDT Date: Mon, 16 Sep 1996 21:42:21 -0700 (PDT) From: Walter Miller Reply-To: Walter Miller To: laser@berlioz.nsc.com Subject: Laser contest QSO Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-laser@berlioz.nsc.com Precedence: bulk As Jim, WB9AJZ, has reported, he and I had another laser QSO across the Silicon Valley with our 5 mW pointer lasers. I made two improvements to my equipment for this try: higher gain in the Burr Brown OPT210 PIN diode/opamp receiver, and a new mechanical mount for the laser. With the higher gain in the receiver I am now able to hear the humming on distant lights. The new mount is an Edmund Scientific #37922 "reverse angle mount" ($34.00) which is a nice miniature mount with very fine pitch screws which tilts a 1.5" by 1.5" plate in two directions. I bolted the small laser onto this mount with a corner iron from a hardware store. The Edmund mount sits on a plate which also holds the Celestron C90 telescope (and the board with the OPT210 looks through the C90). The C90's spotting telescope completes the installation. All of this is mounted on a fairly stiff camera tripod. The spotting scope is boresighted to the C90, and the laser (after adjustment of the Edmund mount) is also boresighted to the C90. To align it, I first pointed my C90 at the bright red beam Jim was pointing my way, and then fiddled with the mount until Jim could see my beam and "talk me in." My attempt at local alignment by viewing the reflection off trees 100 yards away was not too accurate this time, but once I got it close enough it was easy to peak up with Jim giving me feedback on 2m SSB. I also measured the received beam width by stepping it off until the brightness went way down, and I got a diameter of about 120 feet (20 steps each side of my position). At an estimated distance of 12 miles, this corresponds to a 1.9 mR beam divergence. As a final topping to the QSO, I pulled out my video camera and recorded both the sight of the distant laser spot and the detected audio. To get the audio I placed my headphones against the video recorder mike, and that worked very well. It makes a great momento to an enjoyable QSO. 73, Walt ------------------------------------------------------------------------ Walter Miller, AJ6T Saratoga, CA USA CM87 Reply to aj6t@slip.net