Eater wrote:
> Sounds fun. Have you looked into the equipment cost?
Well, I was looking around, and it doesn't seem to matter what
equipment you use.
Here's how I understand this works. You have a TNC (dumb terminal) that
is hooked to a packet modem that is hooked to a radio transceiver. The
packet modem takes the data stream from your TNC and outputs different
tones for 0 and 1 at various speeds, depending on what the packet modem
is capable of (and what the remote end is capable of receiving, I would
presume). The process at the opposite end of the link is same-same, just
in reverse.
But in our case, we wouldn't be using a TNC which outputs just data to
a packet modem. We'd be using a PC acting as a gateway. The PC would be
equipped with a sound card, and as such could act as its own packet
modem. And since the transmission is nothing more than audio
representations of binary data - sound like a modem anyone? - it really
doesn't seem to matter what radios were used, so long as they were
sufficient to provide enough clarity and range to make the link "just
work". That is, of course, presuming you want to handle any wiring that
needs to be hacked up between the various devices to make the audio link
work right.
Given the above observations - presuming I'm correct - you could link
one city block to another with nothing more than a two-pack of $50
radios from wal-mart using GMRS or FRS frequencies. It's too bad that CB
regulations won't let you tie a channel up for more than 5 minutes at a
time, or it would be a very worthwhile alternative. 2 meter HF/UHF/VHF
equipment is the standard for this type of thing, and while it's not
uber-cheap, you can get in to it for a few hundred bucks, including
antennas, if you pick up used equipment and use your brain and hands
more than your wallet.
> It's limited to something like 9600 bps iirc...
yeah the speeds aren't too good, normally. I mean we're talking a
technology that was developed late in the 70's, early in the '80s.
Although the more I look into it, the more that seems to be a limitation
of the modems at the host and client than of the technology itself.
There are some packet modems that can get 56kbps, and some that can get
1.2mbs. The main difference I'm seeing is that the 1.2mbs equipment
relies on a special version of your radio that has the voice-modulation
hardware removed or bypassed. Which makes it inconvenient and
unappealing to most HAM operators, who want to have one unit that does
both. But in our application we're talking about here, we could give a
damn less if the radio could be used for voice transmission, as long as
the speed has been bumped up.
So given what I understand from above about the type of equipment and
the cost, if you were willing to modify a radio to where it had no voice
modulator anymore, and cut the packet modem out of the mix by going
straight out from the PC... If you could maintain a good clear signal, I
don't see any reason why 1.2mb transmissions would be out of our reach.
I mean if we can get megabit transmission speeds from satellite linkups,
why not from radio waves coming from ground level?
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