warren@pluto.UUCP (02/15/87)
Hello, I work at home, but I can see my office if I stick my head out the window; it's about half a city block away. I do not think the authorities would like it if I ran a wire across a busy street (Broadway in Manhattan, in case you care) but I would like to run my terminal at 9600 baud, 2400 is still to slow, and maybe mux a printer. I've been wondering if I could set up an optical or microwave link, although I'm not sure if I want microwaves pointed at my head. Has anyone done this, know of plans or sources? thanks -- /|/~\~~\ |__/__/_/ | /
stu@hpltca.UUCP (02/16/87)
> Hello, I work at home, but I can see my office if I stick my > head out the window; it's about half a city block away. > > I've been wondering if I could set up an optical or microwave link, > although I'm not sure if I want microwaves pointed at my head. > > Has anyone done this, know of plans or sources? When I was at the University of Colorado at Boulder, they had linked the Computer Center with the terminals in the Engineering Center by optical link, using simple infra-red LED's, photodetectors, and lenses. The distance between the E-center and the Computer Center was ~2 miles. The link was MUCH cheaper than running cable or using Ma Bell. Total cost was a couple of hundred dollars. The link speed was high (56 Kbaud? maybe more), and was reliable, except in HEAVY snow or rain. The link worked through normal glass windows (at least I recall there being glass winndows there). Sorry, I don't have plans. However, this link was installed before I got to CU (circa 1973), so I would assume that you could find SOMEONE who makes a beast similar to this. If you can't find anyone who makes one, try sending a letter to Frank Barnes, Electrical Engineering Dept, College of Engineering, University of Colorado, Boulder, CO, 80302 (I THINK that's the right ZIP - ask the U.S. Snail to be sure). If you're desparate, MAIL a message to me, and I'll try to get them for you (I'm still close enough to go down there and find the plans). By the way, you don't want to screw with microwave links -- FCC regulations and all that will make the project VERY un-fun. GOOD LUCK! Stu Bell HP Colo. Integrated Circuits Division U.S. Snail: P.O. Box 301A UUCP: hplabs!hpfcla!hpltcb!stu Loveland, CO 80539
kehres@styx.UUCP (02/17/87)
In article <214@pluto.UUCP> warren@pluto.UUCP (Warren Burstein) writes: > Hello, I work at home, but I can see my office if I stick my > head out the window; it's about half a city block away. I > do not think the authorities would like it if I ran a wire > across a busy street (Broadway in Manhattan, in case you care) > but I would like to run my terminal at 9600 baud, 2400 is still > to slow, and maybe mux a printer. > > I've been wondering if I could set up an optical or microwave link, > although I'm not sure if I want microwaves pointed at my head. > > Has anyone done this, know of plans or sources? At COMDEX/Fall '86, Electronic Systems Technology was showing some RF wireless modems. The writeup from the program is as follows: "Electronic Systems Technology will display the Esteem line of radio frequency wireless modems and the Quest line of wireless computers. Esteem modems allow wireless local area networking of computers and their peripherals within a 38-mile radius. The unit, designed for intra-office and building communications, is easily interfaced using the RS232C interface. The user definable baud rate is from 110-9600 baud, with an RF Data rate of 4800 bps. The packet radio system handles all flow control and uses a 16-bit CRC for error detection and retransmission for error correction." I do not have any experience with this company, but from the write-up, it looks like they may have a product that will fit this application. Tim Kehres Control Data Corporation / Lawrence Livermore National Laboratory ---------------------------------------------------------------- UUCP: {lll-crg,ihnp4!lll-lcc}!styx!kehres ARPA: kehres@lll-tis-b.ARPA AT&T: (415) 463-6852
berger@clio.UUCP (02/19/87)
You can set up a commercial UHF or microwave link, but that could prove
to be expensive. A full-duplex system requires special equipment
(duplexer, split xmit and recv frequencies, etc.) on each end. Have
you considered a laser based communications system? We had one here
a while ago to ship data between buildings located a block away. It
didn't work as well in rainy weather, and the cheap lasers weren't
really intended (or suitable) for 24 hour a day operation. But the
system functioned.
Mike Berger
Center for Advanced Study
University of Illinois
berger@clio.las.uiuc.edu
{ihnp4 | convex | pur-ee}!uiucuxc!clio!bergerhenry@utzoo.UUCP (Henry Spencer) (02/20/87)
> I've been wondering if I could set up an optical or microwave link...
Probably either would work, but optics are going to be a whole lot less
hassle -- easier to work with, cheaper parts, no licensing problems, no
safety or interference worries.
Half a city block should be easy. Find the nearest store (or library) that
has a good selection of electronics books and starting digging; you shouldn't
have any trouble locating a suitable design.
--
Legalize Henry Spencer @ U of Toronto Zoology
freedom! {allegra,ihnp4,decvax,pyramid}!utzoo!henrywarren@pluto.UUCP (03/02/87)
I posted this some time ago. I since discovered that old maps were routing my mail through phri and pyrnj to which we were not connected. If you replied and it bounced, please try again as we are now linked. And thanks to all who have replied. < Hello, I work at home, but I can see my office if I stick my < head out the window; it's about half a city block away. I < do not think the authorities would like it if I ran a wire < across a busy street (Broadway in Manhattan, in case you care) < but I would like to run my terminal at 9600 baud, 2400 is still < to slow, and maybe mux a printer. < < I've been wondering if I could set up an optical or microwave link, < although I'm not sure if I want microwaves pointed at my head. < < Has anyone done this, know of plans or sources? -- /|/~\~~\ |__/__/_/ | /
zabetia@tiger.Princeton.EDU (Mahboud Zabetian) (03/08/87)
In article <250@pluto.UUCP> warren@pluto.UUCP writes: >< Hello, I work at home, but I can see my office if I stick my >< head out the window; it's about half a city block away. I >< do not think the authorities would like it if I ran a wire >< across a busy street (Broadway in Manhattan, in case you care) >< but I would like to run my terminal at 9600 baud, 2400 is still >< to slow, and maybe mux a printer. >< >< I've been wondering if I could set up an optical or microwave link, >< although I'm not sure if I want microwaves pointed at my head. >< >< Has anyone done this, know of plans or sources? I would like to know too. I have a similar problem. I am a junior here and this year my project involves making a high speed transmission link between two computers or a computer or a terminal. I am planning on using infra red LEDs or a semiconductor laser. The goal is to reach speeds in excess of 20000baud. (I am not using fiber optics) My problem right now is to figure out which is better, IR or Lasers. Anybody know? I hear that IR has the drawback of being the same wavelength as the size of fog droplets, therefore fog will block transmissions. How about lasers? What wavelengths can I use with lasers? Thank you all. -- Mahboud Zabetian allegra! --\ zabetia@tiger.princeton.edu 232 Pyne Hall mhuxi! -----\ (609) 452-2285 Princeton University seismo! -----\ (609) 734-0246 Princeton, NJ 08544 attunix! ------ princeton!zabetia
larry@kitty.UUCP (Larry Lippman) (03/10/87)
In article <175@tiger.Princeton.EDU>, zabetia@tiger.Princeton.EDU (Mahboud Zabetian) writes: > I am a junior here and this year my project involves making a high speed > transmission link between two computers or a computer or a terminal. I am > planning on using infra red LEDs or a semiconductor laser. The goal is to > reach speeds in excess of 20000baud. (I am not using fiber optics) > > My problem right now is to figure out which is better, IR or Lasers. Anybody > know? I hear IR has the drawback of being the same wavelength as the size > of fog droplets, therefore fog will block transmissions. How about lasers? > What wavelengths can I use with lasers? Since you are referring to semiconductor lasers, such as gallium arsenide injection laser diodes, you don't have much choice as to the wavelength range of available products: 820 nanometers to somewhat less than 1.0 micron. Infrared LED's are also available only in the same range. So the point is: the propagation of laser diodes and infrared LED's will be at essentially the same wavelength. Fog will be a problem at this wavelength, because of simple optical dispersion like that of visible light, not because of molecular absorption per se. IR absorption on a molecular level results from O-H bond vibrations, which first manifest theselves at around 1.4 micron, with additional absorption bands from about 2.8 to 3.5 microns, 5.8 to 6.4 microns, and 10.5 microns and above. For what it's worth, I have used a four-element array of infrared LED's (Fairchild FPE104) with a single-element phototransistor (Fairchild FPT100) to establish a 9,600 baud data link between two buildings at a distance of 600 feet. The link was reliable during any kind of rain, light fog, and medium snowfall, but would go to hell during heavy fog or snow. The problem one runs into is signal-to-noise ratio on the received signal. A non-obvious problem - until one encounters it empirically :-) - is the serious amount of noise caused by outdoor mercury vapor and high pressure sodium lighting at night. While the 120 Hz frequency of the lighting is << than the data carrier frequency, and can be filtered out, this is not a trivial task because the lighting signal is so HUGE at night compared to the data signal. Finding a rooftop location and using some attempt at optical collimation can significantly reduce the noise resulting from lighting and other outside events. However, my application was an experiment to see what one "could get away with" under worse-case conditions (put the receiver and transmitter outside two windows and aim :-) ). In any event, regardless of location, I believe that any NON-laser diode system is limited to well under 800 feet for reliable operation; 600 feet is more realistic. I never got around to trying a laser diode. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
henry@utzoo.UUCP (Henry Spencer) (03/11/87)
> Since you are referring to semiconductor lasers, such as gallium > arsenide injection laser diodes, you don't have much choice as to the > wavelength range of available products: 820 nanometers to somewhat less than > 1.0 micron. Infrared LED's are also available only in the same range. A thought comes: if you do end up using LEDs, you might want to consider visible light rather than IR. I haven't done the numbers on things like efficiency and sensitivity, but ASSUMING THOSE ARE COMPARABLE, you will find visible-light hardware quite a bit easier to work with during debugging. (It's not suitable if you want your final system to be inconspicuous, of course.) -- "We must choose: the stars or Henry Spencer @ U of Toronto Zoology the dust. Which shall it be?" {allegra,ihnp4,decvax,pyramid}!utzoo!henry
larry@kitty.UUCP (03/11/87)
In article <7760@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes: > > Since you are referring to semiconductor lasers, such as gallium > > arsenide injection laser diodes, you don't have much choice as to the > > wavelength range of available products: 820 nanometers to somewhat less than > > 1.0 micron. Infrared LED's are also available only in the same range. > > A thought comes: if you do end up using LEDs, you might want to consider > visible light rather than IR. I haven't done the numbers on things like > efficiency and sensitivity, but ASSUMING THOSE ARE COMPARABLE, you will > find visible-light hardware quite a bit easier to work with during debugging. > (It's not suitable if you want your final system to be inconspicuous, of > course.) In general, infrared LED's (I am NOT referring to injection laser diodes here) are available with higher output energy than visible LED's of comparable size. It is sometimes difficult to compare specifications of visible LED's versus IR LED's since many manufacturers specify the former in luminous intensity (measured in millicandellas) and the latter in radiometric intensity (mw/steradian). However, if one does fairly compare the specifications, the IR LED's will outperform the visible light LED's in propagation. As an example, the Fairchild FLV104 visible LED is one of the highest intensity devices on the market, providing a typical 150 mcd of luminous intensity. However, its radiometric intensity (which one need be concerned with for long distance propagation) is typically 4.0 mw/sr. Now, this can be compared to a typical high-intensity IR LED, like the Fairchild FPE520, which has a typical radiometric intensity of 50.0 mw/sr. As you can see, we are talking about an order of magnitude greater propagation energy which is available through IR LED's as compared to visible light LED's. There is another advantage of IR over visible light for some applications (like hand-held remote controls). IR tends to reflect rather well off the surface films of many items, and will do a nice job of "bouncing" its way across a room without having a precise aim. Try this with a TV remote control some day: aim it at the ceiling or a wall, and it may still control the set! <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|seismo|utzoo}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
wsr@lmi-angel.UUCP (03/11/87)
I briefly hacked around with sending analog signals optically about 15
years ago. High Power leds and laser-leds were prohibitively
expensive, and therefore out of the question for a hack project. I
decided to try a normal 1 watt flashlight bulb. It was dc biased to
its normal operation (6 volts in this case), and ac modulated roughly
+/- 50%. The whole circuit was a 741 opamp and a darlington
2n2222/2n3055 pair for the output. Feedback was around the whole
opamp-transistor system.
The receiver was a normal photo-diode (this one had a guard-ring, so
it was a bit quieter, noise-wise), attached to a 1 meg pickup
resistor, and amplified by a u736 fet input op amp. The amp was run
gain 1 for dc, and essentially open loop for ac. I mounted this in a
soda can, with one end cut out, and a second soda can section with
both ends cut off holding a soda-can diameter lens with a 6" focus.
This system was focused by eye (you can watch the image forming around
the detector as you get close).
The ultra-hack receiver could easily pick up the hum from street
lights, and car headlights over a 1/2 mile range. What was interesting
was to listen to ripple from the car alternator in the car's light
output. You could tell what rpm the engine was doing. (It was
interesting to watch people shift...).
I could clearly pick up the transmitter (which was attached to an FM
radio as a signal source) over a 1/4 mile range. Up-ing the lightbulb
power should in theory increase the useful distance (by roughly the
square root of the power increase. How about a car headlight? Hmm).
The frequency response of the system was surprisingly good. As long as
the light bulb is in the white-hot range, black body radiation cools
it *quickly* giving an excellent frequency response. As the bulbs dc
bias is turned down, the bulb cools and it radiates a *lot* less. This
slows down the max dTemp/dt, and lowers the high end frequency
response. This was quite noticeable experimentally.
Its truly amazing at how much performance one can squeeze out of
normal flashlight bulbs.
--
Wolfgang Rupprecht {harvard|decvax!cca|mit-eddie}!lmi-angel!wsrzabetia@tiger.UUCP (03/12/87)
-- Mahboud Zabetian allegra! --\ zabetia@tiger.princeton.edu 232 Pyne Hall mhuxi! -----\ (609) 452-2285 Princeton University seismo! -----\ (609) 734-0246 Princeton, NJ 08544 attunix! ------ princeton!zabetia