lance@chief.UUCP (system administrator) (10/01/88)
Hi,
I have a question for everyone. Where can I find information on RF modems?
I would like to possible get a pair of them for a portable and the system
at work. That way I can get things done while waiting for people at offices.
Any help would be appreciated.
Thanks,
Lance Ellinghouse
Chief Numismatics, Inc.
UUCP: {hermix|ucla-an|srhqla|alphacm}!chief!lance
ARPA: ucla-an!hermix!chief!lance@ee.UCLA.EDU
Voice: (818) 884-9141henry@utzoo.uucp (Henry Spencer) (10/06/88)
In article <379@chief.UUCP> lance@chief.UUCP (system administrator) writes: > ... Where can I find information on RF modems? >I would like to possible get a pair of them for a portable and the system >at work. That way I can get things done while waiting for people at offices. I think you are confusing two very different things. The RF modems I know about -- admittedly it's an area I don't know a lot about -- are for use over coaxial cable and the like. RF does not imply radio. Radio modems do exist, but the radio spectrum is a scarce resource and I don't know of any general-use band that would be available for such a purpose. (Before you ask, use of the amateur-radio bands for commercial purposes is strictly forbidden.) -- The meek can have the Earth; | Henry Spencer at U of Toronto Zoology the rest of us have other plans.|uunet!attcan!utzoo!henry henry@zoo.toronto.edu
jec@nesac2.UUCP (John Carter ATLN SADM) (10/09/88)
In article <1988Oct5.232838.15239@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > In article <379@chief.UUCP> lance@chief.UUCP (system administrator) writes: ] ] ... Where can I find information on RF modems? ] ]I would like to possible get a pair of them for a portable and the system ] ]at work. That way I can get things done while waiting for people at offices. ] ] I think you are confusing two very different things. The RF modems I know ] about -- admittedly it's an area I don't know a lot about -- are for use ] over coaxial cable and the like. RF does not imply radio. Radio modems ] do exist, but the radio spectrum is a scarce resource and I don't know of ] any general-use band that would be available for such a purpose. A portable cellular phone with a cellular modem, and a cellular modem on the line at the office will allow you to work remotely, but there are some limits. The cellular modems I've seen advertised are 300 baud (bandwidth restrictions in the cellular phones - but technology overcomes all :-). Cellular phone usage is EXPENSIVE - $35 month + $0.35 minute (cheaper in quantity, or from other cellular suppliers - shop around for the best price). Depends on what you're doing while you wait - I've found that the Toshiba portable's 720k disks hold all the work I can do in short periods, and it's simple to upload to another machine when I return to the office (or by dialup if I'm out of town). -- USnail: John Carter, AT&T, Atlanta RWC, 3001 Cobb Parkway, Atlanta GA 30339 Video: ...att!nesac2!jec Voice: 404+951-4642 The machine belongs to the company. The opinions are mine.
stacy@mcl.UUCP (Stacy L. Millions) (10/10/88)
In article <1988Oct5.232838.15239@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > In article <379@chief.UUCP> lance@chief.UUCP (system administrator) writes: > > ... Where can I find information on RF modems? > >I would like to possible get a pair of them for a portable and the system > >at work. That way I can get things done while waiting for people at offices. > ... RF does not imply radio. Radio modems > do exist, but the radio spectrum is a scarce resource and I don't know of > any general-use band that would be available for such a purpose. A couple years ago I saw an add for some FM radio modems, 4800 bps with a 30 mile range. I have not seen any thing since then so I don't know if they are still being made or not. - stacy -- "He to whom the early bird runs best learns wisdom and patience! ... I can never remember proverbs" - Charlie Brown S. L. Millions ..!tmsoft!mcl!stacy
mark@drd.UUCP (Mark Lawrence) (10/11/88)
%% In article <379@chief.UUCP> lance@chief.UUCP (system administrator) writes:
%% ... Where can I find information on RF modems?
I posted a similiar query earlier and have since discovered a company
that does something like this. The company is DataRadio, Inc. with offices in
Montreal (1819 Dorchester Blvd W., Suite 400, H3H 2P5) and Atlanta (400
Perimeter Center Terrace, Suite 730, 30346). They sell a modem that
will connect up to a radio that will transfer data at 4800 bps. They
claim that it is x.3 and x.29 compliant. The device is called a Modem
Data Link Controller. I quote from the marketing brochure:
Features
. adds data to your existing fixed or mobile radio system
. up to 4800 bits per second
. Collision Avoidance Radio Multiple Access (CARMA) protocol
. uses external VHF, UHF radio transceiver
. shares channel with voice using an efficient carrier detection circuit
. forward error correction for mobile environment
. RS-232 interface at 50-9600 baud with buffering & flow control
. separate digital I/O port for telemetry and alarms
. built-in user controlled data privacy
. available with built-in 5 port mux
Very interesting item of note: these things are addressable; you can
have up to 255 modems in an RF network. It does encryption using a 128
bit key but don't know if that's available on the version sold in
Canada. The vendor uses crosstalk on their demo setups (Does anybody
know whether crosstalk requires a full duplex circuit?)
Henry expressed concern about the legalities of slinging data about on
channels licensed for voice. I haven't called up the office in Toronto
and asked specifically, however, I assume since the company is selling
the things in Canada, they must be meeting the Canadian equivalent of
the FCC's requirements (and it doesn't monopolize the channel for data).
Price is US$1800.
I don't have any financial stake in these people -- just passing along what I
know.
Mark
--
[uunet!apctrc,romed,tulsun]!drd!mark DRD Corporation Pithy Quote
mlawrence@jarsun1.ZONE1.COM (918)743-3013 Jer. 9:23,24moto@cad.Berkeley.EDU (EDIF Committee) (10/24/88)
Assuming you have a voice radio link (none of the massages have specified),
you might get two of the packet modems made for the ham market. There are
a bunch out ther - from 300 baud (HF) to 4800 baud {_(VHF)xD.
They work through the audio of a voice radio and include error correction
etc.
Mike Waters