RF Modulator | Radio Frequency Modulators

RF Modulator (RF Video Modulator & Audio RF Modulator)

A radio frequency modulator (RF modulator) receives baseband input signal and after processing, the output signal is now a radio frequency modulated signal. In the transmission of signals, this is a preliminary step and, more often, transmitted across open air thru an antenna or other devices like a television.

TV RF modulators

Data must first be modulated or pass through some level of conditioning in a format which is readable by the circuitry of the television before it is translated into pictures or images. This is done by a process of combination of carrier wave and standard frequency.

The broadcast signals like PAL and NTSC going through a TV's input like aerial or coaxial are modulated by TV modulators. The function of such modulators is to get the audio/video (A/V) signals whose source can either be from a video, RGB, YUV or internally before generating PAL and NTSC signals.

RF modulators are commonly available as internal component of video cassette recorders or VCRs. Also, some old electronic videogame consoles like Atari 2600, Atari 800, NES, Sega Master System, Commodore 64, and Sinclair Spectrum. Video game systems manufactured during the 80s do not come with internal RF modulator that is why an external unit is provided and connected with antenna jacks of TV sets. The output of RF modulators is relatively poor in quality with respect to the picture. This is because the quality of the image is affected during the modulation process from the source device and the demodulation process in the TV set. The aerial connector, however, is standard for all TV, old and new models alike. Nowadays, modern TV systems have S-Video and component video jacks. This is the reason why game console manufacturers do not include external RF modulators in their products. RF modulators are now available as third-party product designed for specific purpose like in interfacing DVD players with old TV systems.

RF modulators commonly output on channels 3 or 4 in very high frequency (VHF) in North America . Atari game consoles, however, has channels 2 or 3 for RF. In Europe , channel 36 or the ultra high frequency (UHF) is used by default for RF modulator, and an option of tuning to other channels within the UHF range is available for the same.

Most inferior and cheap home TV systems produce a monoaural audio as the process of modulating a TV signal with stereo quality sound is complex. Even new systems which boast two audio inputs have only a combined right and left audio channels or a single and mono audio signal output. Cheap and old systems do not have the capacity to filter the vestigial sideband as compared with professional systems.

Multi-channel video modulators

Early microcomputer's (Microtan 65) main board showing ASTEC 1111EM36 UHF TV modulator in silver casing at top left.

In home audio/video distribution, multi-channel RF modulators are commonly used. There is only one RF output for these devices, however, as regards the input for video and audio, there are multiple terminals. A/V outputs from source devices like DVD, VCR players and even DSS receivers are interfaced to the audio/video inputs of the RF modulator. Then, the RF modulator broadcasts in a programmed frequency which is then received by the TV. Upon powering on the TV, the broadcast signal from the RF modulator is received by the TV and produced from it. However, in community antenna TV (CATV) systems, the process could be cumbersome since high pass, low pass, and notch filters need to be used to filter some frequencies or channels in order for the audio/video signal which is broadcast from the RF modulator to be displayed or produced.

Audio RF modulators

In low-end or old car audio systems, RF modulator is used to interconnect external devices like CD players without upgrading the dashboard or reconfiguring the car audio system's hardware components. To illustrate this, the CD player's headset jack is plugged with the modulator, which then outputs low-power FM radio signal that is subsequently played by the car audio systems upon reception. This process is not immune to some drawbacks like deterioration of signal quality due to interference from high power external devices.

DVD RF modulator

Due to the fact that RF modulators are now third-party products which are sold separately, newly manufactured equipments are now relatively hard to interface with older equipments. The main issue is the poor quality of the output picture due to the demodulation of the TV and that of the RF modulator. With the introduction of high definition and digital TV systems, RF modulators are no longer essential for such equipments.

As regards DVD players, multi-channel RF modulators are commonly employed. This is the key why DVD players do not encounter issues when interfaced with TV systems even though some other devices like AppleTV, DVR, VCR, or game consoles are connected simultaneously with the same TV system. This is because every device operates in a different frequency or a certain channel. To illustrate this, when you turn on the TV and set to Video1, the TV system will output only signals from the VCR or DVD, depending on what component is attached to that terminal. However, when it comes to CATV systems, certain channels are blocked so as not to cause interference with the output signal. Also, some RF modulators may only function with audio only, as previously discussed with car audio systems, but such systems are prone to interference and loss of quality.