Fax machine hack to test your line quality

November 9, 2007 9:17 AM

I heard that there is a way to call a fax machine with a normal telephone, press some keys and the fax machine will speak back your line quality as a number. I can't find any information about this online, does anyone know how to do this? Is this manufacturer dependent?
posted by bumper314 to computers & internet (3 comments total)

I seriously doubt that this works for all fax machines - If nothing else, the FAX standard was designed back when voice synth ment a big, ugly, expensive tag-along box.

If you're worried about your data speeds/quality, DSL reports might be able to help you.

The only 'hack' I've heard involving phone line quality and FAX machines was a Social Engineering thing with the phone company: During BBS days, if your line was dirty, you could call the phone company and complain that you were having to retransmit faxes due to interference, and they'd actually fix it instead of blowing you off (Which frequently happened with data complaints in the 80's.).
posted by Orb2069 at 9:50 AM on November 9, 2007

Yeah, it'd be a special feature of a particular model of fax machine. But there's more:

The only way to measure quality effectively is that your end is looped and the fax machine emits a tone and listens to the result coming back.

Presumably, the scheme you talk about involves the fax machine listening to the DTMF (or whatever, depending on your locale) and comparing that noise against what it should hear. That's pretty lame, considering how much latitude the phone systems permit; I'd be surprised if most consumer electronics was worth the test results.
posted by cmiller at 10:19 AM on November 9, 2007

Never heard of it in fax machines. There are/were (in Aus, & I've been out of the game for a couple of years now) a few phone company test bases where you could do something similiar - send a fax & it returns a report by fax; connect by modem & read the LQ on-screen. Things like attenuation vs freq, noise level & margin, tone twist (phase distortion), etc.

It's possible that somewhere along the line, this rumour got confused with one of the other test bases where you call in, enter a few codes, and get a spoken report of line quality for another line (or it rings you back after doing a test on the calling line). Things like A-B-E capacitance, A-B-E resistance, foreign battery, etc.

I'm deliberately being a bit vague, because while some of this is sort of publicly known the phone companies generally don't want it spread around. The terms FOLDS, MOLDS, SALT (or SULT), & SULTAN may mean something to the right people...
posted by Pinback at 2:06 PM on November 9, 2007