I work as a computer technician on the side and I also fix telephones and computer networks.
I would like to have a simple device that detects whether a line is PSTN or ISDN and if there’s an ADSL sync signal present.
There are such devices on the market, but they cost too much and they have a ton of other functions I do not need. Is there a simple, cheap (sub $100) and as small as possible device that can do these 3 things I mentioned above?
Are there any ISDN circuits out there any more? ETA: Do you mean VOIP?
Detecting a sync signal should be trivial with a small oscilloscope or equivalent, if you already have one. Not sure what would be involved in a simple detector, but I’d start by looking for a cheap DSL interface chip and wiring it to do nothing more than light an indicator if a sync signal is detected.
For some reason ISDN is still widely popular here (Greece).
What does an ADSL sync signal look like on a scope?
Sorry, didn’t realize you were in Europe. ISDN would still be in use in places that haven’t moved on to the newer technologies. It’s a great way to get a lot out of existing copper.
I don’t know, offhand; you’d have to dig into the relevant standards to see if there’s a single coherent frequency you could look for. The Wikipedia entry for ADSL lists them all, with links. (It’s been over ten years since I messed with this stuff and the details fade, fade, fade…)
Since ADSL uses freqs from 25 kHz to about a megahertz, you could look for ANY signals in that range to start with. Or, check a known-ADSL, known-good line to see what’s there. I’d guess there would be sync or ID signals at about 25kHz or 138kHz, those being boundary lines for the overall signal components.
ETA: You might be able to use a similar technique to differentiate ISDN from PSTN - in theory, the latter would have no digital signals on it at all, except for ADSL if it’s present; I suspect there are sync and backchannel signals on ISDN. Complete WAGging from old experience, here, though. ISDN also requires a CPE box of some kind, as far as I know - I don’t think the components can be remote.
Sounds like you need a “data safe” buttset. I’ve got a Harris (now Fluke) TS44 that will alarm if it detects data such as ISDN, Frame Relay, ATM or DSL.
The one thing it won’t do is tell you what kind of data service is on the line. If you really need to know what kind of service is on the line, there are analyzers that can do this, but they’re not inexpensive.
On re-read, I saw the desire to be under $100. On the US used market, the TS44 is selling at around $80-140. New, they’re more like $400.