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An ancillary job of mine is to support an analog phone line for our credit card machine. From time to time AT&T changes out hardware in the core which causes the machine's modem to not connect over the phone line.

Testing the line by plugging in an analog phone is not rigorous enough. Often the phone will have a dial tone and place calls, but there is too much noise for the modem.

I am looking for a hardware tool I can plug into the RJ-11 jack which will evaluate the line quality. I have a budget of up to a couple hundred dollars if necessary. I need to know if the line quality is degraded and unable to carry a modem connection.

I appreciate any recommendations of a tool to do this job.

masegaloeh
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steampowered
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  • Fluke (Laughed when i was first told about them, funny name) will get the job done and are guaranteed to get an accurate result. Expensive though... – Silverfire Nov 16 '11 at 02:34
  • You could always throw the modem line through a sound-card and look at the signal in audacity (using isolation) – Silverfire Nov 16 '11 at 02:37
  • @Silverfire any suggestions for a particular product from them? – steampowered Nov 16 '11 at 02:52
  • A lot of ADSL modem firmware will have info about the attenuation and signal strength of the line when you bring up the status page. That's a quick solution, but you may be after more advanced or additional metrics. –  Nov 16 '11 at 03:53
  • @darvids0n Would that work on a line without an ADSL signal? – Andrew Nov 16 '11 at 05:10
  • @Andrew Probably. You wouldn't get a Signal-Noise Ratio most likely, but I would guess it can still show attenuation so you can determine whether the line is bad. –  Nov 16 '11 at 23:00
  • @steampowered, contact Fluke and describe your problem. They may have more than one suitable instrument and will normally be happy to both recommend one and send out a rep to demonstrate it for you. – John Gardeniers Nov 16 '11 at 23:47

2 Answers2

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Some older modems could perform line testing. You could simply get a pair of modems, and attempt to make a call, then see what link speed you get. Your credit card machine probably just has a standard modem in it.

http://web.archive.org/web/20110907062746/http://www.scn.org/help/linenoise.html

Worthwelle
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Zoredache
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I don't know what tool to buy (nor am I sure if Server Fault is the right place to ask - perhaps EEE?), so I'll suggest this:

If you don't have a cabling contractor that you regularly use, make contact with one. Once you have a cabling contractor, explain your situation, and see what they suggest (or how much they will charge to do the job for you).

Community
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Andrew
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  • "wrong place to ask" - the question is about networking two computers for a professional site. One of the computers happens to be a server. Cabling contractors don't like to get called if there is a simple test which can be performed beforehand. I don't know anyone who keeps a cabling contractor on site. – steampowered Nov 16 '11 at 04:09
  • @steampowered If you are looking for a specific shopping recommendation, that is off-topic for any Stack Exchange site. I don't keep a cabling contractor on site either, but I do have a good working relationship with one - and I can call them for advice or if needs be, book them to do the job for me. Alternatively, contact your telco. – Andrew Nov 16 '11 at 04:49
  • I wasn't looking for an exact product as much as I was looking for an exact tool. Something to give me additional information before I make the call for someone to drive to my location. – steampowered Nov 16 '11 at 04:59
  • @steampowered Perhaps try asking on http://electronics.stackexchange.com/ - though the fastest/cheapest option may still be to talk to the telco responsible. – Andrew Nov 16 '11 at 05:09