DQT1000 Digital to QAM Transcoder Advanced Applications
The introduction of the DRAKE DQT1000 represents the addition of yet another unique product to DRAKE's growing line of products for the reception and processing of digital television signals. The DQT1000 is unsurpassed in combining multiple functionality in one single unit of rack space. It contains two tuner/demods with 8VSB and QAM capabilities, MPEG program filtering, a transport stream multiplexer, a QAM modulator and a low noise high output power agile upconverter. In addition it may be special ordered with a single tuner/demod and a field installable ASI Input Module is available.
The DQT1000 can be remotely controlled and programmed via its RS232 serial interface.
The DQT1000 is capable of transcoding several different digital input combinations into a QAM output on any desired broadcast or cable channel for insertion into a cable system channel map. A program filtering function allows inclusion or deletion of any individual program in the digital transport stream. The following applications detail the possible uses for this truly agile product:
Off-Air/8VSB to QAM Transcoding
The DQT1000 can transcode a single off-air/8VSB digital broadcast signal to a QAM output. The demodulated 8VSB broadcast signal consists of a MPEG2 transport stream (TS) of up to 19.4 Mbits/s. With the appropriate Forward Error Correction (FEC), the resulting TS with this additional "overhead" will still "fit" into the selected 6 MHz output channel using 64 QAM modulation. Null Packets will be added as required.
Multiplexing Two Off-Air/8VSB Broadcast Signals into a 256 QAM Channel
This is probably the most common use for the DQT1000. The standard DQT1000 is supplied with dual demodulators and will accept two off-air inputs. These can be sourced from a single off-air antenna and a splitter or from two separate dedicated off-air antennas. The demodulated transport streams (up to 19.4 Mbits/s each) are multiplexed resulting in a transport stream with a data rate as high as 38.8 Mbits/s. After the addition of the required FEC, the resulting transport stream will still "fit" in the selected 6 MHz output channel using 256 QAM. The DQT1000 may be special ordered with a single demodulator if desired.
Multiplexing an Off-Air/8VSB Broadcast Signal with an ASI Source into a 256 QAM Channel
With the addition of the optional ASI Input Module, the demodulated transport stream from the built-in tuner /demod can be multiplexed with the transport stream supplied to the ASI Input Module. This ASI source could be a file server, a standalone demodulator, a fiber link from a broadcast station, many satellite IRDs, or, in general, any source supplying an ATSC based transport stream not exceeding 19.4 Mbits/s. As in the previous example, if the combined transport stream does not exceed approximately 38.8 Mbits/s, it will still appropriately occupy the selected 6 MHz output channel after the addition of FEC using 256 QAM modulation.
Program Filtering
A "select program" function is provided to allow the operator to select which of the MPEG programs present on the A and B input streams to be included in the output multiplex.
Regenerating a QAM Signal from a Noisy Source
Since the DQT1000 demodulates the input signal (QAM in this case) the resulting MPEG2 transport stream ("digital baseband" signal) is identical to the input channel. It error corrects, then re-modulates the selected output channel with this error corrected transport stream with the desired QAM modulation. Thus, it can be used to "regenerate" a "clean" QAM signal on any output channel
QAM Channel Translation
Typically referred to as channel processing in the cable industry, the DQT1000 can input a QAM signal and effectively "translate" it to a different channel on the output. However, unlike most analog signal channel processors, this is not a heterodyne process. While a hetrodyne processor is excellent for analog signals, for digital signals it is best to use a demod/remod process making full use of FEC (Forward Error Correction). This is done in the DQT1000.
Product Notes
- The 19.4 Mbits/s demodulated transport stream from an off-air broadcast signal is typically composed of one High Definition (HD) signal, several Standard Definition (SD) signals or several SD signals and other "data" related to other services that may be provided by the broadcaster. In general, it can be composed of any combination of HD, SD & "data" signals as long as the combined data rate does not exceed 19.4 Mbits/s.
- Program and System Information Protocol (PSIP) PSIP is a data stream embedded in an ATSC DTV TS that provides information to a DTV receiver/Set Top Box/Cable Card about what the TS (Transport Stream) contains. This ATSC (Advanced Television Systems Committee) DTV (Digital Television) transport stream is the transport stream referenced above as the demodulated output of the DQT1000 tuner demod/demods. It's a MPEG2 transport stream with a bit rate of up to 19.4 Mbits/s.
Although a detailed explanation of PSIP is beyond the intent of this description, it basically includes a number of data tables that detail necessary information about the program in the transport stream and other general system information. The DQT1000 has the capability, if required, to reconstruct new tables in the transport stream associated with the output signal from the table contents existing in the input signal tables. This reconstruction will essentially take into account the data available in the input signals and the requirements for the output signal as dictated by the customer premise equipment (Set Top Box, Cable Card, etc.)
| Drake Digital DQT1000 Technical Specifications | |
|---|---|
| Demodulator Input(s) | Applies to both tuner/demodulators, if so equipped. |
| Input Frequency Range: | 54 - 864 MHz. Off-air channels 2-69, CATV channels 2-135. |
| Menu Selectable Channel Plans: | Standard CATV, HRC, IRC or Broadcast. |
| Input Channel Bandwidth: | 6 MHz. |
| Input RF Level Range: | -28 dBmV to +30 dBmV. |
| Minimum Input Level per Mode: | 8VSB: -28 dBmV, 16VSB: -25 dBmV, 64QAM: -20 dBmV, 256QAM: -15 dBmV. |
| Maximum Input Power (sum of all channels): | Not to exceed -16 dBm. |
| Input Impedance: | 75 Ohms with Return Loss typically 8 dB. |
| Noise Figure: | Less than 12 dB. |
| Image Rejection: | 40 dB. |
| Adjacent Channel Rejection: | 60 dB. |
| Demodulation Modes: | ATSC: 8VSB or 16VSB ITU-A: 16QAM, 32QAM, 64QAM, 128QAM, or 256QAM. ITU-B: 64QAM or 256QAM. |
| Symbol Rates: | Commonly used presets and user programmable. |
| Equalizer Span: | -6 µS to +40 µS. |
| ASI Input | |
| Optional Module: | 270 Mbps with desired transport stream of 10.76 MS/s, 19.37 Mbps |
| Null Packet Processing | Available in the fixed output clock mode. |
| QAM Modulator | |
| Modulation Modes: | 16QAM, 32QAM, 64QAM, 128QAM, 256QAM, 512QAM, or 1024QAM. |
| Symbol Rate: | 1 Ms/S to 7 Ms/S. |
| Forward Error Correction (FEC): | ITU-A (DVB) or ITU-B (DigiCipher® II). |
| I/Q Phase Error: | Less than 1 degree. |
| Carrier Suppression: | 45 dB. |
| Channel Amplitude Error: | Less than 1dB. |
| MER: | Greater than 38 dB with blind equalizer. |
| Analog EAS IF Input | |
| Input Impedance: | 75 Ohms. |
| Operating Input Level: | +30 dBmV ±5 dB @ 45.75 MHz. |
| Auto Switching Level: | +20 dBmV minimum. |
| RF Output | |
| Output Frequency Range | 54 MHz to 1002 MHz. |
| Channel Plan: | Standard CATV, HRC, IRC or Broadcast. |
| FCC Offsets: | Automatic, +12.5 or +25 kHz. |
| Frequency Stability: | ±5 ppm. |
| Maximum Output Level: | +61 dBmV minimum, adjustable downward. |
| Minimum Output Level: | +45 dBmV. |
| Output Level Accuracy: | ±1 dB. |
| Output Impedance: | 75 Ohms with return loss better than 14 dB (within output filter passband). |
| Spurious Outputs: | -60 dBc from 40 MHz to 1000 MHz. |
| Broadband Noise: | Less than -12 dBmV (6 MHz bandwidth @ ±12 MHz). |
| Phase Noise: | -101 dBc @ 10 kHz offset. |
| RS232 Control | |
| Data Link: | 2400, 4800, 9600, or 19,200 baud interface via serial cable |
| RS232 Input: | DB9 connector for connection to modem or PC |
| RS232 Output: | DB9 connector for connection to additional units |
| General | |
| Power: | 90-132 VAC, 60 Hz, 40 W (all options installed). |
| Weight: | 7 lbs. (3.2 Kg.) |
| Size: | 19" (48.3 cm) W x 1.75" (4.45 cm) H x 11.5" (29.2 cm) D |
| Operating Temperature: | 0º C (32º F) to 50º C (122º F) |
Supersedes models DQT860 and DQT861. Specifications, price, and availability are subject to change without notice or obligation.
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