We have frequent problems with telemetry signals from remote sites. More often than not, it is a problem with the phone lines. However, when the line is working but the quality is low, it still causes problems. Trying to explain this to a BT operator is a nightmare. Is there anything available that can plug into a UK telephone socket and give you a measure of line quality, e.g. good, poor? TIA
You can book a site visit from a BT engineer, will give you s/n ratios, line impedance etc. Bt won't do anything about the line though if it is within their tolerance for 'telephone line'. If you need to spec the line as a 'data' line they will reduce the s/n ratio & gain, but charge you accordingly. A standard line is only guaranteed for audio use.
sQuick..
What data rate are you trying to send?
What modulation technique?
Are you using a commercial OTS piece of equipment?
Do you have transmission retry?
What's the telemetry interface to the POTS?
It's pretty simple to gauge the quality of a line in code (assuming you tack on a CRC or some such, or send some known data as a test).
Cheers
PeteS
In the US you are able to buy an inexpensive phone line quality tester. I got one for about $15. I proved to the phone company it was not my internal wiring that was at fault but theirs. The line coming in from the utility pole had a defect in it. It was a high resistance at the point where the wire connected to the phone company's splice box.
Al
yes but interpreting the results is the tricky part. you can "sweep" the line with signal generator or sweep generator at one end and an audio voltmeter at the other using a coupler to inject and measure tones. you can also measure distortion and signal to noise ratios.
however, getting the telco to accept ANY measurement that they did not make as valid is a huge problem.
you might try this free program to generate needed test tones on a computer with soundcard.
and fax at up to 12000 bps.
In the UK, many exchange line cards can do this test on command from the operator. Often, the test will clearly show if the fault is on their side or your side of the NTE (the demarkation between their responsibility and yours).
Yep!
You are asking the OP the right type of questions!
Our local telephone lines are pretty bad. We routinely hear static when making a voice call.
Yet our PCs have no problem getting data rates from 25 to 31 KBS from our ISPs.. Just a good combination of modems, protocols, and software.
Seems to be that if they have the money to lease telephone lines they could put the equivalent of a PC at each site. That might be cheaper than trying to custom engineer a data link.
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