Pic: Example of professional RF Modulator:
RF modulators are used to alter signals from devices such as VCRs, DVD players, media players, and game consoles to a format that can be handled by a device designed to receive a modulated RF input, for example, radio and television receivers. The RF modulator converts the video (and/or audio) output of a DVD player (or camcorder or video game) into a frequency which can be assigned any channel that is compatible with a TV's cable or antenna input. There are many RF modulators available, but all function in a similar manner. RF modulators may also be used to take the audio and video signals from a PAL or NTSC/ATSC composite video, RGB, or other composite AV source, and produce a broadcast RF signal that can be fed into a television's aerial/coaxial connector.
Multi-channel RF modulators are normally used in any place that requires audio/video distribution like stadiums, homes, hotels, malls, airports etc. These devices have numerous audio and video inputs and one RF output. Audio/video outputs from source devices such as a DSS receiver, DVD player, VCR, or are coupled to the audio/video inputs on the modulator. The modulator is then programmed to transmit the signals on a certain channel. The RF signal is then received by the connected TV. When the TV is tuned to the programmed channel, the signal of the source device is accessed. RF modulation can become complex in a CATV system. High pass, low pass, and notch filters must be used to obstruct certain frequencies, so that the modulator can transmit the signal of the source device on that channel. Commercial modulators such as those used in the CATV industry generally include residual sideband filtering which is usually lacking on consumer grade modulators. Audio RF modulators are used in low-end car audio to attach devices like CD changers with no requirement of dashboard hardware upgrades. For example, a portable CD player's headphone jack is linked to the modulator, which outputs a low-power FM radio signal that is played through the car radio. Car FM modulators experience failure of value and interference issues. Soon after devices which would use these types of modulators would be MP3 players and related mobile media players.
Coaxial cable is used as a transmission line for radio frequency signals. Its applications consist of feed lines connecting radio transmitters and receivers to their antennas, computer network (Internet) connections, digital audio (S/PDIF), and distributing cable television signals. Advantage of coaxial over further types of radio transmission line is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors. This allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides safeguard of the signal from outside electromagnetic interference. Coaxial cable conducts electrical signals using an inner conductor (generally a solid copper, stranded copper or copper plated steel wire) enclosed by an insulating layer and all enclosed by a shield, typically one to four layers of woven metallic braid and metallic tape.
The cable is confined by an outer insulating jacket. Normally, the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor. The benefit of coaxial design is that electric and magnetic fields are restricted to the dielectric with little leakage outside the shield. Equally, electric and magnetic fields outside the cable are mainly kept from interfering with signals inside the cable. Larger diameter cables and cables with various shields have less leakage. This property makes coaxial cable a good choice for carrying weak signals that cannot endure interference from the environment or for stronger electrical signals that must not be allowed to radiate or combine into nearby structures or circuits. The characteristic impedance of the cable is determined by the dielectric constant of the interior insulator and the radii of the inner and outer conductors. A restricted cable characteristic impedance is essential because the source and load impedance should be matched to make positive maximum power transfer and minimum standing wave ratio. Other significant properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality. A coaxial RF connector (radio frequency connector) is an electrical connector intended to work at radio frequencies in the multi-megahertz range. RF connectors are typically used with coaxial cables and are intended to preserve the shielding that the coaxial design offers.
Coaxial cable is a type of transmission line, used to carry high frequency electrical signals with low losses. It is used in such applications as telephone trunk lines, broadband internet networking cables, high speed computer data busses, carrying cable television signals, and connecting radio transmitters and receivers to their antennas. It differs from other shielded cables because the dimensions of the cable and connectors are controlled to give an accurate, even conductor spacing, which is needed for it to function efficiently as a transmission line. Widespread applications of coaxial cable include video CATV distribution, RF, microwave transmission, computer and instrumentation data connections.
Radio frequencies are electromagnetic waves operating between 10 (khz) and 1 (Ghz) propagated without guide (wire or cable) in free space. If you have a personal computer that lets you use your home TV set as a video display device, then the computer has a RF generator. This means that this device is generating a RF carrier to carry the video signal information. For the purposes of the FCC’s regulation of cable television systems, this term includes any carrier, modulated, or unmodulated, whether radiated over the air by an antenna or carried by a coaxial cable. This term dates from the early days of radio (hence, the name “radio” frequency) when the only uses for RF were AM broadcasting and ship-to-shore communications. The term is still used today, even though it now includes video and control signals as well as audio.
What precisely does modulating the signal entail? Modulation is transmitting a signal over an extensive range, which will cause to it to suffer from attenuation. Attenuation is a general term indicating a decrease in power (loss of signal) from one point to another. This loss can be a loss of electrical signal. The loss is measured as a ratio of input power to output power. Attenuation is caused by poor-quality connections, defects in the cable and loss due to heat. Attenuation is the opposite of gain. The resolution to avoid such loss is to modulate the signal.
Pic: Example of professional RF Modulator:
The method of modulating the signal means the integration of a signal with another wave of a higher frequency. This reduces the attenuation throughout the transmission of waves over long distances and it increases the range. RF signals are surrounded by the highest frequency signals and are useful in carrying information over large distances. For modulating the signal, what we require is a RF modulator. Likewise, the signal that is received at the other end needs to be demodulated before it can be changed into a usable form. So at the signal reception point, we need an RF demodulator.
The fundamental construction of an RF modulator is not very complex.
The signal that needs to be modulated is taken in as input. It is first passed through a comparator (electronic circuit for comparing two electrical signals) and then through a low noise amplifier (LNA).
The low noise amplifier amplifies the input signal.This is accomplished because the signal loses some power during the transmission and this step is taken as a deterrent measure. The output of the low noise amplifier and the radio frequency wave is mixed in a mixer, to generate the modulated signal. This is the critical method of a modulator's working. But the procedure of radio frequency modulation has a vast number of variations. There are plenty of additional modulation techniques that can be used, for example: Phase Shift Key (PSK), to modulate the signals with the radio frequency. In general, radio frequency modulation is done digitally nowadays. The audio and video signals are RF modulated, before transporting them to the television antennas or cables, which works at that frequency. The modulation and demodulation of the signal, at both the ends, is often the reason behind the good picture and sound quality.
However, current RF modulators that comes integrated into our VCD players, DVD players or gaming system, cause nominal or no damage to the picture and sound quality. Many televisions, mainly the ones manufactured before the advent of DVD players, use coaxial cables and do not have proper A/V inputs. In such cases, you need to buy a peripheral RF modulator to provide your objective. They need an external power supply and if you are using one, then please be sure that you have a power source near your television set. Numerous people are perplexed with RF modulators with video switchers.
Video switchers are devices that help you in connecting more than one device to a single terminal, whereas an RF modulator helps you in attaching those devices to your television. Radio frequency modulators are also used in the fields of defense and aviation. In effect, all radars send signals within the range of radio frequencies. In the aviation industry, the information that is sent to flights is also required to be radio frequency modulated.
Connecting a digital cable box, VCR, and DVD player to a TV that doesn't have AV inputs for the DVD player is a dilemma for people who have coaxial-only televisions. Because DVD players don't have coaxial (RF) outputs, they can't be attached straight to a television with only a coaxial (RF) input. The answer is to acquire a RF modulator, which is a little gadget that converts the AV output from the DVD player to coaxial (RF).It seems as if each home garage across the country has an old, idle TV set sitting inside collecting dust. People don't use them because they think that they can't use today's technology, including VCRs, DVDs, MP3 players, camcorders and gaming systems. With a radio frequency (RF) modulator, it's all possible.
The modulator converts the picture and sound coming from your DVD or gaming system and displays it on the TV screen. Connecting a stereo or TV to a RF modulator: If you're connecting the RF modulator to a stereo or TV, take the three plugs that are connected to the modulator and plug them into the video and audio output jacks on the stereo system. There will be corresponding colors on both the plugs and the output jacks so you know where to put each plug. Plug the modulator's electricity cord into a power outlet. Turn both the modulator and the stereo or TV on to check that you connected them properly. Connecting to a different VHF input source into a RF modulator to both a TV set and a VCR, DVD or cable box is easy. Begin by disconnecting the VHF input source's 75-ohm cable from the TV's terminal and connecting it to the terminal in the back of the modulator marked ANT IN. Then get a 75-ohm coaxial cable (often provided with the RF modulator or it can be purchased online) and connect it on the modulator's terminal marked TO TV terminal and to the TVs terminal marked 75-ohm VHF/UHF. Plug the modulator's electricity cord into a power outlet. Turn on all three devices to make certain that you connected them correctly.
If you need a device to convert voice and data signal into a form that can be transmitted then you need a RF modulator. It is also designed to convert separate audio and video signals from a video camera, computer, portable VCR or satellite receiver) into VHF TV signals. It is ideal for TV's that don't have composite video inputs. It is also used to run a secondary TV with the same programming. RF Modulators have become popular in cases where you may need a single signal that is generated by a DVD player, video camera or other device that needs distributed to hundreds of TV’s.
In cases like this it is expensive to place a Cable STB and Satellite STB at every TV, so inherently using a low cost or professional DVB modulator eliminates that need because you can use one STB connected to a RF modulator which can be distributed to unlimited television sets via coaxial cable as long as the televisions.
Sports stadiums are a great tool for showing how these can bring down the overall costs since when you’re at a sporting event and head to a snack stand or use the bathroom, walking through the event halls you’ll see televisions littered everywhere showing the event you’re attending so you don’t miss out on the action.