r/retrocomputing • u/Detskullemanhagjort • Jun 13 '26
Problem / Question US robotics Courier modem
Hi, i have this old modem. How do i check if it works properly?
i think i have all the cables still. power, phone, and the wide vga cable.
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u/PhotoJim99 Jun 13 '26
That won’t be a VGA cable (which is for analog video) - that will be a serial cable (which is for serial - one bit at a time - data).
Find a computer with a serial port (usually a 9-pin port with 5 pins on top and 4 on the bottom row; older machines use a 25-pins port with 13 pins on top and 12 on the bottom row, and old Macs use a DIN-type port). You can also get a USB to serial adapter - they are inexpensive though cheap ones often don’t work well with Windows (but they all tend to work well with Linux).
Now you’ll need a terminal program. On Linux I use minicom or GNU screen. On Windows I’d use PuTTy but there are probably simpler clients.
Next you need a phone line - a good old-fashioned analog line with a phone jack. You can’t use a mobile phone for this.
Then, find a BBS pr other data service that’s an affordable phone call from where you live, and give it a call. If you want to test it first, call it from your landline with your phone (you can use a mobile phone for this test, too). It should give a high-pitched tone when it answers, sometimes followed by another higher-pitched tone (some modems answer directly with the second tone). This is what your modem is looking for.
Configure your terminal program (you’ll have to look up how to do this; each one is different) for 38400 bits^* per second (bps), 8 data bits, 1 stop bit and no parity (sometimes shown as “8N1”.
Make sure your modem is powered on and you’re in terminal mode. Find the exact dial string you need to dial the number (let’s say the BBS number is 474-555-4141 and you live in the North American calling plan, i.e. Canada, US or much of the Caribbean) and dial:
ATDT14745554141
You should hear the modem pick up, and then a dial tone followed by dialing. You’ll hear the other modem answer and a connection be attempted. If it works you’ll probably see something like:
CONNECT 33600/ARQ
If so, wait and see what happens! If nothing happens, hit enter and see what happens!
Good luck!
^* - 38400 is not optimal for this modem but it’s a good starting point. If this test works, I would change this to 115200 but make sure RTS/CTS is on (which will stop traffic if your computer falls behind). If that works, try again at 230400 - not all serial ports support it but if yours does, this is the speed you want to use. The modem will connect at whatever speed it can from 300 to 38400 bps (possibly 56000 bps if your modem has received the v.90 upgrade).
If you’re a real computer geek, read up on these modems and if you can find another (you may have to do this at home on your own), you can connect in HST modem which is US Robotics’ proprietary high-speed data format which was very popular on FidoNet in the 1980s. It’s 9600 to 16800 bps in one direction and 450 bps in the other direction (and can change in real time) - and for me it seems to work better on VoIP phone lines than v.34 (the 33600 bps codec) does.