computer signal is it digital or analog

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jblueink

Joined May 27, 2008
24
my question is computer signal, thats the signal sent and received by computers system are they in digital or analog.but computer work with digit. the communication between the ground based stations and the space satellite is what kind of communication and also what kind of signal is used?
 

mik3

Joined Feb 4, 2008
4,843
my question is computer signal, thats the signal sent and received by computers system are they in digital or analog.but computer work with digit. the communication between the ground based stations and the space satellite is what kind of communication and also what kind of signal is used?
Computers use digital signals to communicate between the internal and peripheral devices. Some devices, like the modem and the sound card, output and receive analogue signals, but they convert these analogue signals to digital signals by using DAC (sound card) or FSK (modem). Thus they still communicate with digital signals with the PC. For the communication between the earth and the satellites they use microwaves as far as i know.
 

StephenDJ

Joined May 31, 2008
58
The concept of "off" or "on" (0 or 1) is the very foundation on which a digital computer is built. In a computer, regular voltages may be used to represent these states, but in order to transmit these states without wires over long distances, a constantly changing analog signal may be needed to represent the 0s and 1s which are digital. This process is called modulation, and it can exist in the format mik3 mentioned above (FSK) or any of other many different formats. (Hope this helps.)
 

beenthere

Joined Apr 20, 2004
15,819
Frequency shift keyed. One tone for logic high, another for low. Google is really great for finding out about these things.
 

sax1johno

Joined Oct 20, 2007
17
"the communication between the ground based stations and the space satellite is what kind of communication and also what kind of signal is used?"

It honestly depends on the system . . . but on modern systems, the uplink (to the satellite) is always digital because it has to be encrypted (you can't encrypt analog signals reliably or quickly).

Modern satellite systems use Binary uplinks (to the satellite) and downlinks (to the ground station) using phase-shift-keying (PSK) -- check out google for that one. The signal is often in the Ku-band, C-band, or X-band -- but it is not necessarily limited to that. Also, the signal is almost always polarized.

Commanding of satellites especially relies on encrypted binary for the uplink -- otherwise you could have people sending commands to the satellites, which could really wreak some havoc. As for the downlink, subscription services like XM and DirecTV have encrypted downlinks, GPS and FTA (Free-to-air) television and radio are not encrypted.
 

sharma2k7

Joined Dec 10, 2007
36
Communications inside computer are pure digital communication, Digital data over Digital medium.LAN Communications are digital data over analog medium AM & FM's are analog data over analog medium,When we talk about Digital system Usually we are talking about Digital information over Analog medium.
 

StephenDJ

Joined May 31, 2008
58
In reference to what is FSK, often a zero-crossing detector is used in hardware to detect when the analog signal voltage passes through zero-volt level as it rises and falls. Every time it crosses zero twice (rise/fall), a cycle is detected. The rate at which it does this is how the frequency is detected. For example, 1200 Hz could represent a logic 0, while 2400 Hz could represent a logic 1.
 
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