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I found the following:
Why 48V voltage is used in telephone systems ?
The -48V voltage was selected because it was enough to get through kilometers of thin telephone wire and still low enough to be safe (electrical safety regulations in many countries consider DC voltages lower than 50V to be safe low voltage circuits). 48V voltage is also easy to generate from normal lead acid batteries (4 x 12V car battery in series). Batteries are needed in telephone central to make sure that it operates also when mains voltage is cut and they also give very stable output voltage which is needed for reliable operation of all the circuit in the central office. Typically the CO actually runs off of the battery chargers with the batteries in parallel getting a floating charge.
The line feeding voltage was selected to be negative to make the electrochemical reactions on the wet telephone wiring to be less harmful. When the wires are at negative potential compared to the ground the metal ions go form the ground to the wire instead of the situation where positive voltage would cause metal from the wire to leave which causes quick corrosion.
What is the differnece between PDH and SDH microwave?
We use (8,13,15,23)GHz ODU at vertical & Horizontal Polarization.But what factors depend on design Vertical & Horizontal Polarization on those above frequency.
can any body tell me what is LOG PERIODIC ANTENNAE?
Egerly waiting for reply.
Thanks and regards,
Mahak
Hi all ,
Can any body tell what measures that can be taken to minimise multipath fading when there is no possibilities for space diversity and there is no water body in the
profile?During the Transmission planning a planner use vertical or horizontal polarization.When we’ll use vertical & Horizontal polarization.Please give me the technical answer.
Q.Why polarization is needed in the GSM antenna? What would happen if there were no electrical and mechanical polarization?
A.To avoid space diversity,Now a days crosspolarised(90* pol. difference b/w TX & RX) GSM antennas are used which can simultaeously work as a TX and RX both,without interference.
why bit error rate has a default value of 10e-6?
How circular polarizaion of EM is achieved? Can vertically or horizontally polarized antenna receive circularly polarized waves?
Reply to :
Can any body tell what measures that can be taken to minimise multipath fading when there is no possibilities for space diversity and there is no water body in the
profile?Methods to mitigate multipath fading:-
1) Strong coding(convolutional or turbo) and interleaving bit errors at the receiver
2) RAKE RECEIVERS – Most important – to combine energy of most significant multipath components
3) Inner loop power controlAll this is reference to CDMA/WCDMA
How aperture of MW antenna is related to HOPE distance.
Hi,
sorry to say you are not sending mail my questions answer.you’ve sent mail but that was not my question answer.pls send appropriate answer.basic difference between sdh and pdh
“SDH differs from PDH in that the exact rates that are used to transport the data are tightly synchronized across the entire network, made possible by atomic clocks. This synchronization system allows entire inter-country networks to operate synchronously, greatly reducing the amount of buffering required between each element in the network.”
SDH = SONET
http://en.wikipedia.org/wiki/Synchronous_optical_networking#External_linksPDH
http://en.wikipedia.org/wiki/PDHOverview (a bit old…)
http://www.gare.co.uk/technology_watch/sdh.htmRubel
Regarding the Negative voltage being suplued to BTS particularly in Ericsson BTS. The reason is
1: This prevents corroson.
2: This protects BTS during Lightining.
3 and the main reason, the Noise generally runs to + terminal of the Battery so we use -ve terminal in order to increase the speech level quality.
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