Fischer.pa@XEROX.ARPA (08/27/85)
Summary of replies: a few, none extensive or particularly knowledgable ( I was suprised ). Motorola apparently makes terminals that operate in some commercially acceptable band and at rates between 4800 and 19.2k baud (?). Anyone have a product name for this device? NASA has a design for a communication system which is satellite linked and requires an antenna only about an inch long (hence could be put in a wristwatch sized unit). This latter seems ideal, but who would build it? Anyone have a reference to a paper from NASA on it? Rumor: Dec or IBM (more likely the latter) is equipping their field reps with radio terminals. That's all. If I follow up I'll send more info. Of course, if any other kind souls out there would like to comment further I'll gladly play "editor" once again... (ron)
john@anasazi.UUCP (John Moore) (08/28/85)
In article <1018@brl-tgr.ARPA> Fischer.pa@XEROX.ARPA writes: >Summary of replies: a few, none extensive or particularly knowledgable ( >I was suprised ). If you really want to connect portables via radio, you might consider amateur packet radio technology. Terminal node controllers can be purchased for less than $300 from several suppliers. They will interface via audio (and PTT control) to any voice quality radio transceiver (amateur OR commercial), and will send data at 1200bps half duplex using a modified HDLC protocol. They are legal for use on the commercial bands (assuming, of course, that your commercial radio is properly licensed). They will operate through repeater stations allowing a walkie-talkie/TNC/portable_pc to communicate throughout an entire metropolitan area. They communicate via RS232 ASCII with a simple command set. These are currently used by commercial operators for telemetry, and are also used by the US Govt for data communications with their hurricane hunter aircraft. -- John Moore (NJ7E) {decvax|ihnp4|hao}!noao!terak!anasazi!john (602) 952-8205 (day or evening)
mikey@trsvax (09/13/85)
Cellular phones won't work for modems. At least not now, and not with off the shelf modems. I know some people who use Radio Shack model 100's and 200's on their phones, and they get OK results, but the problem is cell handoffs droping the carrier. Also, 300 baud is EXPENSIVE over a cellular phone. Even when you are sitting still, the cells can be reconfiguring, causing problems with modems. Sure, you can get manual modems that won't hangup on a dropped carrier, or even modems that are modified so that the timeout is lengthened for drop, but then you're talking "custom", not off the shelf. If it is for a dedicated use, I'd use 1200 bps modems wired directly to the phone. Since the phone is half duplex except for the handset, you can wire direct from the Rx and Tx portions of the modem and not use it's filters. Both modems (at the host and at the portable) will have to be modified to not drop line on short carrier interuptions. There are probably a host of other problems, just that these are where I'd start before I'd lay out my game plan. mikey at trsvax