Answer / guest

u know every metal oxidises by giving its valence
electron.so metal corrode with time.metal corrodes due to
environmental effects like moisture etc.suppose u r giving
+48 then metal will loose its electron quickly & will be
oxidised. So the metal will be corroded quckly & u have to
replace it .But if u give -48 then metal will not loose its
electrons because the metal wire will be negatively
charged.if metal somehow looses its electron then metal can
draw electron from the current becoz the wire is negatively
charged.so metal will not corrode with time.Thats why we
uses -ve supply(-48v).Moreover if we use +ve supply(more
load more corrosion)ie if load is high metal will be corrode
Quickly.in our MSC sites we use load upto 600 amps.in this
case if we will use +ve supply we have to replace the wires
frequently.if we use -ve supply there will be no problem

Answer / vineet kumar

-48V is used in the telecom to prevent noise in
communication. Also it prevents the formation of sulpates on
the battery terminals giving it a longer life.

Answer / vinit panchal

it is used for removing noise.............
because noise will be not affected more in -ve level so -48v dc is used for removing noise

Answer / jagatheeson

if we use +ve 48 v,normally tel.cables laying through
ground and it will interact with neative(ground) cable
will be corroded and noise will be in phones,To avoid this
normally nagative grounding is done in telecoms.

Answer / matulungin

to provide talk battery..^^

96 The high-frequency response in RC active filters using op-amp is due to A BW B Gain C Gain,BW product D High frequency

1 Answers  

---

How receiver detect that which is information signal and which is carrier signal and how it seprate both at destination?

4 Answers   Airtel,

---

Define what do you mean by donor and acceptor impurities?

0 Answers  

---

WHAT IS THE USES OF PLC?

16 Answers   Avanceon, BMW, Sony, Usha Martin,

---

1.Explain 3D radar. 2.Method of mobile signal jamming. 3.Frequency hopping spread spectrum. 4.How does op-amp works in common mode? 5.Which flip flop is known as universal flip flop and why?

0 Answers   BEL,

---

---

Define slew rate.

0 Answers  

---

What are the advantages of single phase bridge converter over single phase mid-point converter?

0 Answers  

---

what is the use of -3 db frequency?& why does it exist in filters?

1 Answers  

---

what are thyristor family and explain it?

1 Answers   Takreer,

---

The peripherals of the computer(like keyboard, monitor) are connected through buses directly or is there any interfacing device present in the CPU?

3 Answers   NTPC,

---

Define virtual grounding?

0 Answers  

---

Where lcr meter is used?

0 Answers  

---