communication 4

[manv]

sirs,
ilike to know why d.c supply +ve terminal is grounded
in communication systems i didnot get correct or acceptable reply

 

[Heydave]

The purpose is extend the life of the conductors and splices in the wiring. The negative charge relative to ground (and possible moisture) will have a plating effect on the metallic conductors instead of corrosion. Note the relative corrosion of the positive terminal of a car battery relative to the negative terminal. The negative voltage on communications circuits became standard for this reason and is therefor used in communication systems and cables that are not exposed to the outside world.

You will also find that many systems use a current to "seal" connections. Without this current, splices can appear to go open circuit. This can be a problem with socketed CMOS ICs since their inputs draw no current. Note also that any connectors or switches that carry a signal to very high impedance inputs may appear to fail as well with time. This can be configuration DIP switches and jumpers. Don't count on designers of PC motherboards and add-on cards to know much about this. It can account for older PCs getting "flakey". A preventive measure is to remove and re-insert all jumpers and connectors and toggle all dip switches to clean the contacts. Do this whenever you open a system for upgrades and mods.

 

[mgrinfeld]

It is also to assure proper reference for currents and voltages thus, avoiding mireference due by noise and other factors. Communications standards depends a great deal on voltage levels

 

[Heydave]

In telephony, currents are more important for signalling than voltage. Many systems dot not have a direct connection to ground but "float" the feed current (sometimes with a current source). There is a high impedance ground connection to bias the circuit negative. This scheme allows for higher power line voltage induction into a circuit without injecting it into the balanced pair.

 

[betkro]

Yeah!. let's go back to the germanium era.

 

[tomatge]

Heydave

At last ... this question, or variants of it, has been posted many times. Your first paragraph is the clearest and most logical answer I recall seeing ... star from me !