Electronic – Testing a phone cable length


This story must be quite familiar:

From the start, I've had a problem with my phone/ADSL line: Cracks, hisses and other noise on the phone – enough to make it occasionally unusable, along with an ADSL connection that is slow and as far from reliable as it can get without failing completely. Naturally, the ISP and phone company insist that the problem is on my end.

My house was renovated about 3 years ago and all indoors wiring was replaced, before we moved in permanently. When my phone went dead three months ago, I finally replaced the last pre-renovation length of cable, the one that went under the garden to connect to the telecom entry point.

Admittedly, that cable was a mess. It was a heavy-duty Cat-3 cable, but it had been in that underground channel for almost 20 years – the insulation had been obviously damaged in some spots, exposing the wires. I think that something may have actually eaten through the cable here and there.

Unfortunately, replacing that cable did get the dial tone back, but it did not solve any of the other issues. I have disconnected and re-connected all accessible joints in the line, and done all the usual tests like disconnecting the house wiring (including the alarm system), to no avail.

Rather than have another bout with the phone company or start going after the newer 3-year old phone cables, I was wondering if there was a way to test the phone line from the telecom entry point to the distribution point inside the house.

Of course, I am talking about something more useful than a simple continuity/resistance test, which does not reflect how the line will behave under an AC signal. I know that there are specialized cable testers, but they are very expensive and very few technicians have them. Ideally I'd use an oscillograph along with a frequency sweep generator to test the frequency response of the line, but I do not have access to any of these instruments at this time.

Is there anything else that I could try, preferably something that does not require a lot of cash, or tearing cables out of the walls?

PS: I don't mind building a circuit or two, as long as I have the schematics – I have not designed a new circuit for quite some time, and I'd rather not do it if I can avoid it.

Best Answer

Testing the wiring is an interesting project in and of itself, but there may be a simpler and more effective way to address the overall system, at least before resorting to that: Can you take the DSL modem and a laptop to the service entry point and try it right there, thus eliminating the wiring issue? If it works there, then you work on testing your wiring; if it doesn't the problem would seem to be either with the carrier/drop or with the modem itself.