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Tranmission of Digital Signal?

04/28/2010 4:17 PM

How could you transmit digital signal for long distances without converting to analog form?

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Guru
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#1

Re: Tranmission of Digital Signal?

04/28/2010 6:43 PM

Through wires or wireless? One way or both ways? What do we understand with long distances? Meters, kilometers, how many?

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#3
In reply to #1

Re: Tranmission of Digital Signal?

04/29/2010 4:24 AM

long distance means in kilometer more than 5km......................is it possible via wire??

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Guru

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#7
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Re: Tranmission of Digital Signal?

04/29/2010 9:52 AM

yes thats mostly how its done already, as data sent by digital means is easier to read if interference is present.

why do you mention analoge ?How could you transmit digital signal for long distances without converting to analog form

http://en.wikipedia.org/wiki/Telecommunication

it can be sent over power lines, telephone lines, microwave links, fibre optics, laser point to point,(same as fibre optics but without the fibre),

it has error checking

http://en.wikipedia.org/wiki/Power_line_communication

http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521879071

google link

http://www.google.co.uk/search?q=digital+communications+over+wires&sourceid=ie7&rls=com.microsoft:en-gb:IE-SearchBox&ie=&oe=&redir_esc=&ei=S47ZS9TNLIX20gT68qRM

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#11
In reply to #3

Re: Tranmission of Digital Signal?

04/30/2010 5:36 AM

While commending earlier responses, let me add this line description of some of the many ways you can achieve transmission of digital signal. Take note of the indicated media.

Source(Digital PBX with E1 port)------Medium(Microwave radio or Fibre optic cable)-----Destination(Digital PBX with E1 port)

Source(Data switch e.g. cisco with Ethernet port)-----Medium(Microwave radio or Fibre optic cable)-----Destination(Data switch)

Source(Data switch via Transmit/Receive VSAT)------Medium(Satallite)-----Destination(Data switch via Transmit/Receive VSAT)

Source(TV signal via earth station)------Medium(satellite)----Destination(Receive-only VSAT)

cheers,

ethobil

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#12
In reply to #11

Re: Tranmission of Digital Signal?

04/30/2010 5:41 AM

Sorry, Post #11 was intended as a response to original post #1

cheers,

ethobil

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Guru
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#2

Re: Tranmission of Digital Signal?

04/28/2010 8:16 PM

A few options are telegraph, semiphore, smoke signal, fiber optics. You may want to provide some quantitative details.

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Guru

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#14
In reply to #2

Re: Tranmission of Digital Signal?

04/30/2010 12:44 PM

you missed out drums

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Guru

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#4

Re: Transmission of Digital Signal?

04/29/2010 5:14 AM

What do you mean by "without converting to analog form"?

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Guru
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#5

Re: Tranmission of Digital Signal?

04/29/2010 7:06 AM

Fibre-optic cables.

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Guru

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#6
In reply to #5

Re: Tranmission of Digital Signal?

04/29/2010 9:08 AM

Right on!

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Guru

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#8

Re: Transmission of Digital Signal?

04/29/2010 9:59 AM

transmit digital signal for long distances without converting to analog form

this line is confusing because it would if its voice start of as analog be converted to digital and then sent other end reverse it digital back to analogue.

if its analogue and you don't want to convert it to digital that can done also.

thats how am radios work, amplitude modulation.

and the early telephone system was analogue

http://en.wikipedia.org/wiki/Analog_telephone_adapter

http://en.wikipedia.org/wiki/Plain_old_telephone_service

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#9

Re: Tran mission of Digital Signal?

04/29/2010 2:43 PM

The basic method is by phase shift keying.

Imagine a single tone being broadcast. The radio wave is represented as a sine curve. This shows the basic energy pulse of the radio wave.

Now, if we can interrupt the transmission and start over, the sine curve is thrown off, or restarted. If we can track where on the sine curve that interruption occurs, then we can assign a binary value to that interruption or phase shift.

There are several modulation schemes available for various mediums. The simplest is Binary Phase Shift Keying, or BPSK. If the shift occurs between 0 and 180 degrees on the sine curve, it is interpreted as 0, if between 180 and 360 (or 0), then it is interpreted as a 1. Quadrature Phase Shift Keying (QPSK) looks at four sections where shifts can occur, 0-90, 90-180,180-270, 270-360, but now since we have four points, the interpreted signal can be two bits: 00, 01 ,11 or 10. There are other modulation schemes as well.

As you can imagine, the amount of data assigned to a shift key depends on how well the receiving device can detect and measure the shifts. For a long time, QPSK was about as good as it got in radio. Now, with better processors, and better radios available, we can not only measure the phase shifts, but measure the amplitude of the signal at the time of the shift as well. 16-QAM (quadrature amplitude modulation) is used in most high speed mobile broadband services (cell phones and connection cards) and can provide four bits of information per shift.

All of this is made possible by a bunch of math I don't even pretend to understand.

More information is available on Wikipedia http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation

All of the above applies to both wired and wireless connections. With wired connections higher data rates are possible because the environment is controlled. There are a bunch of issues surrounding modulation a radio signal. Books have been written on the subject. Suffice it to say that signal interference, the frequency being used, the equipment in use, load on the network and such affect how well the transmission works, but at the heart of it, the modulation scheme is how digital information moves over an analog signal.

The links from peterg7lyq have more great information.

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#10

Re: Tranmission of Digital Signal?

04/29/2010 5:32 PM

For long distances, any signal needs to be mounted on another "analog" signal, as it is done on microwaves, cable, satelite. Even, digital TV signal is mounted on a carrier. You will need a modem's to do so. You will need more modem depending on quantity of users for that signal. In optical, the signal needs to be converted to analog.

Rafa :)

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#13

Re: Tranmission of Digital Signal?

04/30/2010 12:05 PM

If the digital signal is in a computer file, just attach it to an email and send it off.

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Guru

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#15
In reply to #13

Re: Transmission of Digital Signal?

04/30/2010 4:56 PM

GA: there are now lots of reasonably priced Ethernet connectable instruments/controllers out there which, you can access from your PC.

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