cameronjames@snoc01.enet.dec.com (James Cameron) (02/26/91)
For a charity canoe race checkpoint, I want to connect two Tandy 102 laptops over a distance of around 500 metres, with the least wiring possible. The machines have integral direct-connect Bell type modems as well as an RS-232 connector. [fyi; the Bell modems are otherwise useless in Australia] My options appear to be 1) RS-232 cabling (two core plus shield earth), 2) Standard telephone cabling (two core, twisted pair), 3) Field telephone cabling (one core, with earth return), 4) Radio-modems. I want to avoid option 1 due to the high cable cost and the risk of damage due to electrical storm activity and other forms of induced EMF. Option 4 looks a little complicated unless I can find prebuilt radio modems that I can just plug in and run. So down to options 2 and 3... I guess for these I'd use a telephone power supply, but I don't know how to build one nor how it is connected. Can anyone help me with this? How would I achieve single core operation? I've seen the recent discussions in sci.electronics about FM transmitter chips for radio modems, but does anyone have any information on prebuilt units? Regards... James Cameron Digital Equipment Corporation (Australia) P/L (cameronjames@snoc01.enet.dec.com)
alewis@gmuvax2.gmu.edu (alewis) (02/27/91)
In article <1991Feb26.094452@snoc01.enet.dec.com> cameronjames@snoc01.enet.dec.com (James Cameron) writes: >For a charity canoe race checkpoint, I want to connect two Tandy 102 laptops >over a distance of around 500 metres, with the least wiring possible. The >machines have integral direct-connect Bell type modems as well as an RS-232 >connector. [fyi; the Bell modems are otherwise useless in Australia] > >My options appear to be > > 1) RS-232 cabling (two core plus shield earth), > 2) Standard telephone cabling (two core, twisted pair), > 3) Field telephone cabling (one core, with earth return), > 4) Radio-modems. > [discussion of 1 & 4 omitted] > >I guess for these I'd use a telephone power supply, but I don't know how to >build one nor how it is connected. Can anyone help me with this? How would I >achieve single core operation? Just hook the two modems together with standard phone cord. No power supply should be necessary unless your modems derive their operating power from the phone company. If they use the Hayes command set, here's how to make them talk to one another. Give one modem the command "ATD". The "AT" stands for attention, the "D" means dial. This will cause the modem to send a carrier as if the phone has already been dialed and answered. On the other modem, type "ATA". That means attention, answer. Then you should be all set. Note that after the dial that modem will expect a connection within a certain period of time or it will timeout. There might be a way to defeat this, or else you'll just have to coordinate at both ends. Alan (:^|
ftpam1@acad3.alaska.edu (MUNTS PHILLIP A) (02/27/91)
In article <1991Feb26.094452@snoc01.enet.dec.com>, cameronjames@snoc01.enet.dec.com (James Cameron) writes... >For a charity canoe race checkpoint, I want to connect two Tandy 102 laptops >over a distance of around 500 metres, with the least wiring possible. The >machines have integral direct-connect Bell type modems as well as an RS-232 >connector. [fyi; the Bell modems are otherwise useless in Australia] > >My options appear to be > > 1) RS-232 cabling (two core plus shield earth), > 2) Standard telephone cabling (two core, twisted pair), > 3) Field telephone cabling (one core, with earth return), > 4) Radio-modems. > >I want to avoid option 1 due to the high cable cost and the risk of damage due >to electrical storm activity and other forms of induced EMF. Option 4 looks a >little complicated unless I can find prebuilt radio modems that I can just plug >in and run. So down to options 2 and 3... > >I guess for these I'd use a telephone power supply, but I don't know how to >build one nor how it is connected. Can anyone help me with this? How would I >achieve single core operation? > >I've seen the recent discussions in sci.electronics about FM transmitter chips >for radio modems, but does anyone have any information on prebuilt units? > >Regards... >James Cameron >Digital Equipment Corporation (Australia) P/L >(cameronjames@snoc01.enet.dec.com) Telephone modems often operate fine without the -48V supply from the telco line. The trick is to get them to dial without waiting for the dial tone; this will depend on the modem and perhaps how it is programmed. Another option would be "short haul modems", which convert RS232 to RS422 and are good for a kilometer or so. Philip Munts N7AHL NRA Extremist, etc. University of Alaska, Fairbanks
bobb@vice.ICO.TEK.COM (Bob Beauchaine) (02/28/91)
In article <1991Feb26.181823.17434@ims.alaska.edu> ftpam1@acad3.alaska.edu writes: > Telephone modems often operate fine without the -48V supply from the >telco line. The trick is to get them to dial without waiting for the dial >tone; this will depend on the modem and perhaps how it is programmed. > I have owned two Hayes compatible modems, and both were quite content to dial sans dial tone (much to the dismay of my wife, who usually happens to be on the line when I try this). /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\ Bob Beauchaine bobb@vice.ICO.TEK.COM C: The language that combines the power of assembly language with the flexibility of assembly language.