Best DVB-T Modulators / Multiplexers

RF Modulators

RF modulators are not used only in antenna systems (MATV/SMATV). Sometimes, the distribution of signal A/V signals via coaxial cable (after conversion to RF signal) is much simpler and less expensive than other solutions - especially in situations where the signal has to reach multiple points (receivers). RF modulators can be divided into two main groups, depending on the character of the output signal - digtal (DVB-T) modulators and analog modulators. Other sub-divisions may be based on the kind and number of inputs (channels), output frequency range etc.

What are types of digital modulation?

Digital modulation is similar to analog modulation, but rather than being able to continuously change the amplitude, frequency, or phase of the carrier, there are only discrete values of these attributes that correspond to digital codes. There are several common digital modulation schemes, each varying separate sets of parameters. The simplest type is called On Off Keying (OOK) where the amplitude of the carrier corresponds to one of two digital states. A non-zero amplitude represents a digital one while a zero amplitude is a digital zero. A specific implementation of OOK is Morse Code. Frequency Shift Keying (FSK) is a form of frequency modulation where a certain frequency represents each binary value. Finally, Quadrature Amplitude Modulation (QAM) uses combinations of amplitudes and phases to represent as many as 1024 digital states.

Digital vs analog modulators

Using an analog RF modulator is by far the cheapest solution. A digital modulator costs more, but it has a number of advantages associated with the distribution of the signal in digital form - good and identical image quality in the whole network, possibility of distributing HD content, effective use of RF spectrum (several A/V signals can be distributed within one RF channel). In digital modulation the signal can easily disconnect from noise, which is much more difficult when using analog modulation. Most of the signals that we transmit in nature are analog, like voice signal and it is much simpler to complete analog modulation comparing with digital. But when using digital modulation, you require transmitting through an ADC converter before transmission and a DAC at the end of the receiver for recovering the unique signal. The extra phases needed to transmit DM enhance both the price and difficulty of the transmitter as well as receiver.

DVB-T Modulators - Basic information

DVB-T is an abbreviation for "Digital Video Broadcasting — Terrestrial"; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998. This system transmits compressed digital audio, digital video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing (COFDM or OFDM) modulation.

It is also the format widely used worldwide (including North America) for electronic news gathering for transmission of video and audio from a mobile newsgathering vehicle to a central receive point. Instead of carrying one data carrier on a single radio frequency (RF) channel, COFDM works by splitting the digital data stream into a large number of slower digital streams, each of which digitally modulates a set of closely spaced adjacent sub-carrier frequencies. In the case of DVB-T, there are two choices for the number of carriers known as 2K-mode or 8K-mode. These are actually 1,705 or 6,817 sub-carriers that are approximately 4 kHz or 1 kHz apart. DVB-T has been further developed into newer standards such as DVB-H (Handheld), which was a commercial failure and is no longer in operation, and DVB-T2, which was initially finalized in August 2011.

DVB-T offers three different modulation schemes: QPSK, 16QAM, 64QAM and has been adopted or proposed for digital television broadcasting by many countries using mainly VHF 7 MHz and UHF 8 MHz channels. DVB-T as a digital transmission delivers data in a series of discrete blocks at the symbol rate. DVB-T is a COFDM transmission technique which includes the use of a Guard Interval. It allows the receiver to cope with strong multipath situations. Within a geographical area, DVB-T also allows single-frequency network (SFN) operation, where two or more transmitters carrying the same data operate on the same frequency. In such cases the signals from each transmitter in the SFN needs to be accurately time-aligned, which is done by sync information in the stream and timing at each transmitter referenced to GPS.

Modulation - spontaneous or deliberate change of signal parameters. If sinusoidal signals are modulated, this process may cause changes in amplitude, frequency or phase of vibrations.

In the case of rectangular waves (often used in digital technology), the modulation process is subject to the width, amplitude, position (arrangement) and density of pulses. The frequency of changes caused by modulation is much lower than the wave frequency. An example is the modulated sound of a variable frequency alarm siren.

The modulation device is called the modulator. Demodulation (in other words: detection) is a process that is inverse to modulation. A device called a demodulator or detector reproduces a modulation signal from a modulated waveform.

If the communication has a two-sided character (eg full duplex), then one device modulates the transmitted signals simultaneously and demodulates those that it receives (modulator-demodulator, or in short a modem).

Modulation and modulators proposed by Thor Broadcast are necessary in virtually every AV set, especially in such, in which the computer is involved.

The signal used in them must be capable of transmission via the telecommunications network. Physical limitations cause information to be distorted due to noise, distortion and crosstalk from other signals sent in the same facility. Therefore, choosing a good Thor modulator is so important. The modulated message after overcoming all these obstacles must be so correct that the recipient can extract useful data from it.

All ThorBroadcast offered items are on acceptable price level.

There are 3 basic modulation techniques:

Analogue modulation of:
- Amplitude;
- Phase;
- Delta-Sigma (ΔΣ).
Pulse-Code:
- PCM – Pulse-Code Modulation;
- DPCM – Differential Pulse-Code Modulation;
- PWM – Pulse-Width Modulation;
- PAM – Pulse-Amplitude Modulation;
- PPM – Pulse-Position Modulation;
- PDM – Pulse-Density Modulation.
Keying:
- Amplitude Shift Keying - ASK
- Quadrature Amplitude Modulation - QAM
- Frequency-Shift Keying - FSK
  - Multiple Frequency-Shift Keying - MFSK
  - Gaussian Frequency Shift Keying - GFSK
  - Minimum Shift Keying - MSK
  - Gaussian Minimum Shift Keying - GMSK
- Phase-Shift Keying – PSK;
- Spread Spectrum Systems:
  - DSSS –Direct Sequence Spread Spectrum;
  - FHSS –Frequency Hopping Spread Spectrum;
  - Pulsed-FM;
  - OFDM – Orthogonal Frequency Division Multiplexing;
  - CDMA –Code Division Multiple Access.
- RTTY –Radio TeleTYpe

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RF Modulators

What are types of digital modulation?

Digital vs analog modulators

DVB-T Modulators - Basic information