Pardon me if this is slightly Off-Topic, but I am hoping that there are
others interested:
From: Or Botton <[EMAIL PROTECTED]>
> A friend of mine and I are thinking about trying to setup a LAN between
> our computers. He lives afew houses away from me (about 2, 3 minute
> walk), so obviously putting a cable isnt a solution. The internet
> bandwidth at our ISP's can be very low at rush hours, and direct
> modem to modem connection have become quite a futile idea, thanks to
> our phone company who have increased the prices sky-high. (they
> "fixed" it by giving discount to ISP dial-up numbers. G, thanks.)
> It was then when I thought of the idea of using Radio. I heard of
> afew people who did it before.. And ofcourse, I have no idea where
> even to start.
> So, if you have any ideas, comments, suggestions, I will be glad to
> hear it!
> Basicly, the idea is to have only our two computers connected.
> If we're going to use a LAN, then we'd rather use IPX. Both
> machines will either run on DOS or Windows (we have both installed,
> and as you can guess from my being in this list, we're both beavily
> experienced with DOS.). We can also put up a Linux server if needed,
> though we dont really have any any knowledge how to mess with it.
> Still, the target 2 computers are a DOS&Windows combo, and cannot
> be changed to any other OS (sorry david! ;)
> So.. if you have any ideas.. please help. :)
I have a number of - admittedly - half-baked ideas along this line:
1. An RF (Radio Frequency) link. For short range, a pair of walkie-
talkies or CB (Citizen Band) radios on a relatively quiet frequency
should be adequate to connect a couple of modems. If you got a "ham"
(Amateur Radio) license, you could have your "own" assigned frequency.
Due to radio interference, you will need a fairly robust communications
program. I recommend using FM (Frequency Modulation) as being better
than AM (Amplitude Modulation). I have seen a simple schematic using
FSK (Frequency Shift Keying - FM using two frequencies) using a PLL
(Phase Lock Loop - CD4046 chip, I think) suitable for use within a house,
but it would need amplification to get the range and, if powerful
enough to work, it would probably need a license to be legal. If you
are concerned about security, there are fancier communications
protocols such as code-hopping PCM (Pulse Code Modulation) that you
could experiment with. For purposes of comparison, I hear that 28.8 K
is "pretty good" for the commercial cellular telephone and modem
combination.
2. A microwave link. The transmitter could be unlicensed due to low power
if you used a couple of "pizza-sized" dish antennae to beam the signal.
A separate transmitter and receiver at each end would probably be cheapest
and simplest, although there are ways to switch, and use only one dish
at each end. Probably the trickiest part would be a GaAsFET (Gallium
Arsenide Field Effect Transistor) final stage and upconverter transmitting
in the Gigahertz range. LNAs (Low Noise Amplifiers) and block
downconverters are readily available as satellite receivers. This will
give you an idea of the pricing, too. This could keep up with a network
card in each PC, and because of low power and a relatively tight beam,
would have an innate (low) level of security. If you wanted to
experiment, all the fancy protocols could be tried, too.
3. An optical link. If you salvage the "guts" from a couple of CD-ROMS
(this is the part using old computer parts), I think you could use the
autocenter/autofocus features to keep it focussed on the focal plane
of a simple thin lens (or mirror). You need good-quality lenses the
width of the beam, but because lasers are monochromatic, you don't
need fancy achromats (multiple component lenses). If you modulate the
outgoing laser, spread the beam to several inches, so that most of it
goes around raindrops, and focus the incoming beam so that it imitates
the spot seen in a normal CD-ROM, and the data processed as if it was
being read from a CD. This requires a line-of-sight from your place to
his, but I think it could be made to emulate a drive on the other
system (IDE or SCSI), or hooked up to network cards. It should be
cheap, fast and relatively secure, although it will fail in fog, or if
something gets in the way.
1 and 2, at least, copy known, working, systems. No. 3 is the one I
consider most appealing, although I consider it the least developed. I
foresee at least one problem with the autofocus controls interacting at
both ends of the loop, so one end should have a large capacitor time
constant (or maybe be disabled) to avoid having them "fight" each other.
Boyd Ramsay
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