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For transmission through a radiowave.
Laury Homenick
Wiki User
∙ 10y ago- without being modulated on a carrier, the signal will not transmit
note: once modulated, in some systems, the carrier can be removed/suppressed and the signal will still transmit OK. but the carrier must first be modulated to transmit.
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What is a demodulator?
The process of separating the original information or SIGNAL from the MODULATED CARRIER. In the case of AMPLITUDE or FREQUENCY MODULATION it involves a device, called a demodulator or detector, which produces a signal corresponding to the instantaneous changes in amplitude or frequency, respectively. This signal corresponds to the original modulating signal
What is the difference between baseband coaxial cable and broadband coaxial cable?
Iam pretty sure that baseband coax was 50 ohm and was used for networking computer, were broadband coax is 75 ohm and used in the cable tv industry. A baseband signal is the original signal before it is modulated onto a carrier, mulitplexed or mixed. A broadband signal contains many channels which have been modulated or multiplexed onto a common carrier. The significant difference is the bandwidth of each. The impedance of the cable which carries either of them is totally irrelevant to the definition.
Which device is used to convert analog signals to digital signals?
In datacommunications this is a modulator/demodulator, commonly known as a modem. In electronics a digital to analog converter (DAC) chip is used to convert digital signals to analog and an analog to digital converter (ADC) chip to convert analog signals to digital. Some chips are available which include both ADC and DAC functionality. There are thousands of different types of DAC and ADC sytems and which one to use largely depends on how fast you want to do the conversion.
How does the FSK modulator circuit work?
The FSK (Frequency Shift Keying) modulator circuit works by shifting the carrier, a sine wave of a given frequency, to another frequency back and forth as the input signal changes. On the receiving end, the demodulator works by detecting one or both of the frequencies, often with a band-pass filter, regenerating the input signal. You can also use a signal processor to convert the carrier from time domain to frequency domain with a fourier transform, and then pick off the signal that way.) The FSK method of modulating/demodulation is typically limited to low frequency signal rates, such as 300 bits per second. You can also modulate multiple input signals onto one carrier, but the workable signal rate of each goes down. (In one signalling example, six analog inputs were used to duty cycle modulate six 10 hertz pulse trains, which were then FSK modulated onto one carrier. The receiving end had six band-pass filters, and six converters back to the analog domain.) If you are going to modulate more than one signal, you need to pick the frequencies carefully, so that their harmonic spectra do not intersect, otherwise you could get cross-talk if there is distortion in the carrier.)
Why Doppler vor uses in place of conventional vor?
Conventional VOR A conventional VOR (CVOR) has three Amplitude Modulated (AM) signals encoded on a VHF carrier: 1) a 30 Hz variable (VAR), which is modulated by the antenna, not the transmitter; 2) a 9960 Hz subcarrier, which is in turn frequency modulated (FM) with a 30 Hz reference (REF) signal; 3) and a voice / identifier channel, which includes 1020 Hz "Morse code" identifiers and aural voice signals. The CVOR antenna is a slightly directional antenna, which means it works best in one direction and worst in the opposite direction. This antenna is physically rotated clockwise at 1800 rpm (30 Hz). Imagine one observer (receiver) on a line that is magnetically North of the VOR and another observer on the line that is magnetically East of the VOR. Suppose the VOR station transmits a constant amplitude carrier (in reality, the VOR carrier amplitude isn't exactly constant). The VOR carrier is fed to the spinning antenna. The observers see the VOR carrier increase in amplitude when to antenna is pointed toward the observer (peak) and decrease when the antenna points in the opposite direction (valley). Since the antenna rotates 30 revolutions per second, the observer sees 30 peaks and valleys in the carrier amplitude, the carrier is amplitude modulated with a 30 Hz signal. The phase of the 30 Hz modulating signals perceived by the two observers in our example differ by 90 degrees (North observer sees peak 90 degrees before East observer sees peak). Since this signal's phase varies with position relative to the VOR, the signal is called the variable channel (VAR). In order for the VAR channel to be useful, we need a reference 30 Hz signal (REF). This signal must be perceived by all observers as the same phase, regardless of position relative to the VOR. Here is the problem: the VAR 30 Hz signal is already modulated on the carrier. If the REF 30 Hz signal is modulated onto the carrier without processing, a receiver would find two 30 Hz signals (just one signal if REF and VAR signals are in phase). How would the receiver know which signal is the REF and which is the VAR? To get around this problem, the VOR takes a 9960 Hz carrier and frequency modulates this carrier with the REF 30 Hz signal. The modulation index is 15, meaning the 9960 carrier has a deviation of 450 Hz (30 Hz times 15). In other words, the subcarrier varies between 9510 Hz to 10410 Hz (9960 +&- 450 Hz). This frequency excursion occurs 30 times per second (30 Hz). The subcarrier signal spectrum does not overlap with the spectra of the VAR or aural signal; therefor it can be amplitude modulated on the RF carrier. The reason for frequency modulation of the REF signal on the 9960 carrier, as opposed to amplitude modulating the REF signal, is that the AM detector in a VOR receiver would still output two 30 Hz ambiguous signals and a 9960 signal, all summed together. The VOR receiver has an AM detector which recovers the VAR, 9960 Hz subcarrier, and aural information (called the VOR composite video signal (COMP)) from the RF carrier. The VOR instrumentation processor takes the detected VOR signal , and processes the signal as follows: 1) COMP is processed through a low pass filter that preserves 30 Hz to get the VAR signal; 2) COMP is processed through a high pass filter to reject the VAR and aural signals, then an amplitude limiter, and then though an FM detector to get the REF signal. The FM detector could be a discriminator (used in the bad old days), or a phase lock loop (used in modern equipment); 3) COMP is not processed by VOR instrumentation; however it may be filtered to please the listener, i.e. range filter (1020 Hz bandpass), voice filter (200 to 3000 Hz bandpass). VOR bearing (magnetic direction away from the VOR) is simply the phase angle of the VAR signal minus the phase angle of the REF signal. Doppler VOR The difference between Doppler VOR (DVOR) and CVOR is in the method of encoding the VAR signal on the VOR carrier. The REF and aural channels are the same for both VOR types. To understand DVOR, one must understand the Doppler effect. The classic example is of a stationary observer standing near (not on) a railroad track. The train's horn (source) is moving at a positive velocity toward the observer. The observer hears the horn at a higher pitch than some one on the train hears. As the train passes, the observer on the ground hears the horn at a lower frequency than the person on the train because the velocity of the horn is negative (moving away from the ground observer). This is an example of Doppler effect for pressure (sound) waves. Doppler also applies to radio waves (and light for that matter). To understand how DVOR works, here is a ridiculous illustration: suppose a complete CVOR station, except with a non-spinning omnidirectional antenna (antenna works the same in all directions) is placed on a rail car. The rail car is on a circular track with a diameter of approximately 13.4 meters. The rail car runs really fast: 30 laps per second! (I told you the example is ridiculous.) An observer some distance away from the moving VOR will observe the VOR carrier frequency increase as the rail car comes toward the observer and a decrease as the rail car move away. Since the VOR comes and goes 30 times per second, the carrier frequency is frequency modulated by a 30 Hz carrier. Moving a VOR around a track at a tangential velocity of 1260 meters per second isn't practical. The way a DVOR "moves" the VOR is to have an array of evenly spaced omnidirectional antennas mounted on the 13.4 meter diameter circle. The number of antennas can be as many as 48. Except for "make-before-break" overlaps, only one antenna is connected to the transmitter at any given instant. Each antenna in the array is activated one at a time, in sequence (next antenna on the circle). If the number of antennas in the array is 48, each antenna will be on for 7.5 degrees of 30 Hz (694.4 microseconds). Less expensive systems would use fewer antennas, and each antenna would be on for a longer period of time. The 48 antenna array would require a 48 throw rotatry switch, that can be switched electronically or by a synchronous motor. Each antenna would have to be fed by a transmission line that is the same length as the other antennas. It is important to understand that the VAR signal is encoded by the time-domain spacial velocity of the signal caused by switching individual antennas. It would be a mistake to believe the other antennas are used as a phase array to make a rotatable directional antenna. If the antenna "rotates", the VAR signal is amplitude modulated; therefore a CVOR. If the antenna "moves" spatially in time, the VAR signal is frequency modulated; therefor a DVOR. Does it take a different VOR receiver to process DVOR? No, a VOR receiver does not "care" if it receives DVOR or CVOR. The spectrum of the CVOR REF signal is a narrow signal at the RF carrier frequency (fc) (between 108 to 117.95 MHz), and two side bands, one at fc + 30 Hz and the other at fc - 30 Hz. The DVOR REF signal has the same spectrum components as the CVOR REF signal, with the addition of sidebands at (plus and minus) 60 Hz, 90 Hz, 120 Hz ... and on (with diminishing in amplitudes). The VOR receiver does not react to the sidebands at 60 Hz and above because the VAR signal is separated by a low pass filter. After this low pass filtering, the spectra of the CVOR and DVOR VAR signals are the same.
Why would digital data have to be modulated onto an analog signal?
For transmission through a radiowave.
Which happen first the modulation or the multiplexing?
A terminal may transmit several application, at a time. All such data of that terminal is multiplexed, and this multiplexed signal is modulated onto a carrier.
What is a demodulator?
The process of separating the original information or SIGNAL from the MODULATED CARRIER. In the case of AMPLITUDE or FREQUENCY MODULATION it involves a device, called a demodulator or detector, which produces a signal corresponding to the instantaneous changes in amplitude or frequency, respectively. This signal corresponds to the original modulating signal
What is the difference between a cellular phone and a telephone?
In an analog phone, the mechanical energy of sound (speech) is picked up by a microphone (mic) and converted into an (analog) electrical signal. This signal is then put through whatever electronics stages are required (if any) to get the signal onto a phone pair for transmission to the receiver. In a digital cell phone, the mic picks up the sound and converts that into an analog electrical signal. That analog signal is then sent to an electrical stage called an analog-to-digital (A to D) converter. Once the signal is digitized, it can be treated as a data string and amplified and broadcast (to the cell hub) as such. An incoming call is a digital data string that is D to A converted in the phone and then the newly recovered analog signal is made to be heard by the user. The difference between the two is the conversion and re-conversion (analog to digital and digital to analog) in the digital cell phone.
What is difference between modulated wave and carrier wave?
Carrier Wave: A carrier wave is a high-frequency electromagnetic wave that is used as the "carrier" or the base signal in a modulation process. It is typically a pure sine wave with a constant frequency and amplitude. The carrier wave by itself does not carry any information; it serves as a vehicle to carry the information from one location to another. In AM and FM radio broadcasting, the carrier wave is the primary signal transmitted by the radio station. Modulated Wave: A modulated wave is the result of combining the carrier wave with an information signal, such as an audio signal or data. Modulation is the process of varying the characteristics of the carrier wave (either its amplitude or frequency) in accordance with the information signal. There are two common types of modulation: Amplitude Modulation (AM) and Frequency Modulation (FM). In AM, the amplitude of the carrier wave is varied in proportion to the amplitude of the information signal. This variation encodes the information onto the carrier wave. In FM, the frequency of the carrier wave is varied in proportion to the amplitude of the information signal. This variation encodes the information onto the carrier wave. The modulated wave contains the information that needs to be transmitted, and it can be demodulated at the receiving end to retrieve the original information.
What is difference between modulator and demodulator?
Modulation is used when information is available in analog form that varies the frequency and/or amplitude of a lower frequency wave, depending on the information it carries. The role of modulation is to place this information onto a carrier frequency that can be transmitted more readily and with least loss of information. There are three fundamental types of modulation - frequency modulation, amplitude modulation and phase modulation. In each of these, a carrier frequency is modulated by a lower frequency, to form a modulated carrier wave. A modulator modulates the carrier frequency, while a demodulator detects the modulation on the carrier wave and recovers the original lower frequency waveform at the destination. For many years the modulated carrier wave was converted to a radio signal. Now it is often an electrical signal which is sent down a teleohone line; the information is usually a set of pulses going between computers. When computers are connected to each other in a two-way conversation, the MOdulator and DEModulator are combined into a single device called a MODEM.
What portion of the telephone network still depends on analog signals?
Analog data transmissions occurs every time you log onto the internet using your pc, your modem, and your telephone line.
What is the difference between digital and analog electromagnetic signals?
There is no modulation of a Digital Circuit.Modulation is placing information onto an analog circuit to transport thatinformation to a distant location to be decoded/demodulated.Having said that, you can modulate a digital signal in dozens of ways,(Modem) and you can also modulate an analog signal dozens of ways(AM Radio Station, CB Radio, Walkie Talkie, FM Rock Station).NoteWhat this question may really be asking about is something like:"What are the differences between using an analog signal and a digital signal when you want to encode some information for transmission?"so that has now been posted as a separate question.
What is the difference between baseband coaxial cable and broadband coaxial cable?
Iam pretty sure that baseband coax was 50 ohm and was used for networking computer, were broadband coax is 75 ohm and used in the cable tv industry. A baseband signal is the original signal before it is modulated onto a carrier, mulitplexed or mixed. A broadband signal contains many channels which have been modulated or multiplexed onto a common carrier. The significant difference is the bandwidth of each. The impedance of the cable which carries either of them is totally irrelevant to the definition.
Which device is used to convert analog signals to digital signals?
In datacommunications this is a modulator/demodulator, commonly known as a modem. In electronics a digital to analog converter (DAC) chip is used to convert digital signals to analog and an analog to digital converter (ADC) chip to convert analog signals to digital. Some chips are available which include both ADC and DAC functionality. There are thousands of different types of DAC and ADC sytems and which one to use largely depends on how fast you want to do the conversion.
MODEM stands for?
It comes from the term MOdulator DEModulator.A modem converts a digital signal from a computer into an analog signal, so that can be transferred down a telephone line and then at the other end it is converted back into a digital signal so that it can be sent into the receiving computer. These two processes are known as modulation and demodulation.A modem is a Modulator and Demodulator. It's like a bridge between computer and ordinary telephone lines. Telephone lines only accept analog signals but computers only accept digital (binary) signals so modems help link them.The data is changed to represent 2 audio frequencies. These noises are superimposed onto a phone line audio. This is known as 'modulation'. The incoming signal of course has to be changed back again to binary data, this is known as 'demodulation'.The word modem is shorted for "Modulator-demodulator" referring to it's original use.Modem = MoDem = Modulator + DemodulatorModem is the device that modulates digital signals from Internal Network into analog signals onto analog lines towards ISP & demodulates analog signals into digital signals for use in Internal Network.
How does the FSK modulator circuit work?
The FSK (Frequency Shift Keying) modulator circuit works by shifting the carrier, a sine wave of a given frequency, to another frequency back and forth as the input signal changes. On the receiving end, the demodulator works by detecting one or both of the frequencies, often with a band-pass filter, regenerating the input signal. You can also use a signal processor to convert the carrier from time domain to frequency domain with a fourier transform, and then pick off the signal that way.) The FSK method of modulating/demodulation is typically limited to low frequency signal rates, such as 300 bits per second. You can also modulate multiple input signals onto one carrier, but the workable signal rate of each goes down. (In one signalling example, six analog inputs were used to duty cycle modulate six 10 hertz pulse trains, which were then FSK modulated onto one carrier. The receiving end had six band-pass filters, and six converters back to the analog domain.) If you are going to modulate more than one signal, you need to pick the frequencies carefully, so that their harmonic spectra do not intersect, otherwise you could get cross-talk if there is distortion in the carrier.)
