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Vector Product Manual

phones at that site are in frequent use. If you can hear such noises, you

will have a target to aim for. Then try the same call with the phone

connected at the demarcation point where the phone lines are terminated

by the phone company. Be sure that your other internal wiring is

disconnected when you make the call. If the line is clean, the trouble may

be in your inside wiring. If the line is still noisy, the problem is either with

the phone company or the phone wiring at the other end.

Check out your inside wiring. How does the line get from the

telephone company demarc point to your codec? You may want to route a

separate line away from other lines or electrical circuits. Make sure there

are no cable staples that go through the cable! What kind of wire is used?

We strongly suggest twisted pair phone cables  if you are using quad

wire, you may be picking up extra noise. If you are buying cable, consider

using Category 3 (or higher) computer network cable.

Are there other phones, modems, fax machines or devices on your

line? We suggest that your POTS codec be the only thing on the line. Even

if the other equipment is turned off, the extra circuitry on the line may

limit your modem performance. If you need to share the line with other

equipment, consider putting in a simple switch to isolate the codec.

Are you located at an AM transmitter site? If so, we strongly suggest

using a telephone line RF filter with good attenuation in the AM broadcast

frequency range. In really stubborn cases, you may need to filter the line at

the telephone company demarc point and at the back of the codec.

Assuming that the inside wiring checks out OK at each end, it

probably is time to start talking with the phone company. Just a caution,

though  they are now being deluged with calls from Internet users who

feel that their modem performance is being affected by their phone lines.

It is probably not in your best interest to stress the word modem in your

conversations with the telephone company. They will probably just give

you a terse dissertation on how they are not required to support modems

above the 2400 bps level.

If there is audible noise on the outside line, go right ahead and

report it. If the problem is weather related (such as with rainy weather),

make the call when the line is actually acting up. They will do an initial test

through their computer system. If they see something wrong, they will

dispatch a repair person to deal with it. The problem will likely be some

imbalance between the line and ground, may be due to a bad cable, or a

bad line protection device. If they dont see a significant problem by

looking through their computer system, you may have to do some talking

to get them to dispatch someone. Be persuasive, but dont try to dazzle

them with your technical competence or assertiveness training.

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Vector VN8912 Handbuch Seite 53