Q. Can I use Linear’s amplifiers to distribute DTV?
A. Yes, Linear’s DA series amplifies all video signals between 54 MHz and 1 GHz. Television, including DTV, is broadcast between 55 MHz and 800 MHz. Our new generation of amplifiers increases headroom to reduce distortion and accommodates digital signals. In addition, they offer more robust power and greater EMI rejection.
Q. When do I use a bi-directional (BID) amplifier and when do I use a high headroom (HHR) amplifier?
A. Either amplifier can be used with DTV. The BID amplifier has a 5-42 MHz return path designed for cable modems and interactive cable boxes (pay-per-view). Use the HHR amplifier for installations where an antenna is being used.
Q. When is Linear going to make a DTV modulator?
A. A modulator is not needed for “off-the-air” DTV. Modulators are only used to distribute local video sources. Currently, there are no video sources that provide the ATSC (DTV) data stream. When DVD players or VCRs that generate HDTV signals become available, we will design a solution to distribute them.
Q. How do NTSC and DTV differ?
A. NTSC and DTV differ in picture format, lines of resolution, modulation methods when transmitted, and audio encoding.
NTSC is an analog RF transmission with a picture format of 4:3. The resolution rate is 525 lines with 480 lines of active interlaced material. Interlaced means that the 480 lines are divided into two fields; even numbered lines are transmitted during field one and odd numbered lines are transmitted during field two. Each field is drawn on the screen every 60th of a second, this is known as 480i. The audio is transmitted using MTS stereo and Dolby Pro Logic®.
DTV or ATSC is a digital video standard and is transmitted using 8VSB modulation. There are 18 variations on the standard, with many having an aspect ration of 16:9. All DTV tuners are compatible with all 18 standards. The three main standards include 480p, 720p, and 1080i. The 480p and 720p are progressive formats, which allows the entire picture to be drawn in a single pass. The 1080i is interlaced and, like NTSC, is drawn in two passes of two separate fields. Only the 720p and, 1080i displayed in a 16:9 format are considered to be true HDTV. 480p is considered standard television (SDTV). The audio is encoded using Dolby Digital, offering up to 5:1 channels of digital sound.