What is the preferred signal strength for QAM/ATSC frequencies?
QAM (Quadrature Amplitude Modulation) is a method extensively used by major cable television providers to transmit digital television content through the same networks as analog cable and high-speed internet. Primarily utilized for delivering high-definition programming and on-demand content, QAM broadcasting often involves encrypting specific channels. To access encrypted channels, viewers typically need a set-top box or CableCard-equipped intermediary for authentication. Cable providers may choose to encrypt all channels, excluding legally required local channels broadcast digitally over the air in the United States. There are hardware appliances known as 'QAM Plants' designed to accept various inputs, like HDMI, and output a QAM transport stream over standard coaxial cable. SnapStream Servers can receive, record, and search unencrypted QAM broadcasts (referred to as 'Clear QAM'), but currently lack the capability to process encrypted QAM broadcasts.
ATSC (Advanced Television Systems Committee) is the sole standard utilized in North America for over-the-air television broadcasts following the 'DTV transition.' Similar to QAM, ATSC is a digital format capable of high-definition transmission. Notably, SnapStream Servers record ATSC broadcasts in the same file format as QAM streams. This standard is prevalent for capturing and delivering digital content in the North American region.
The hardware utilized in SnapStream QAM/ATSC Servers is identical to that used in all other servers, with the sole exception being the TV Tuner boards.
Specifications & Requirements
The quality and strength of the signal supplied to tuners in digital ATSC/QAM broadcasts are crucial due to the exponential logarithmic scale of cable signal measurement and the preferences of most receiving hardware. In contrast to analog broadcasts, where video and audio are assembled on the tuner board, digital broadcast processing involves dealing with a more complex, pre-packaged, and encoded stream. This makes processing digital broadcasts less forgiving of anomalies and signal strength variations, requiring a fundamentally different approach.
Signal strength is typically measured in dBmv (decibel millivolts), where zero dBmv equals 1 millivolt across 75 ohms. Although it's a voltage measurement, digital tuners often require an overall weaker signal strength compared to analog counterparts, marking a notable difference in signal processing requirements between the two.
The specification for QAM signal strength on SnapStream Servers is as follows:
Range at Ch2 (57Mhz): -12dBmv to +16dBmv
Range at Ch134 (855Mhz): -18dBmv to +7dBmv
Overall supported range: -12dBmv to +7dBmv
Because of this relatively low ideal signal strength, the use of powered or amplified splitters is discouraged.
Applies to Version:
Any SnapStream Server or Encoder utilizing ATSC/QAM as a source