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Difference Between QAM and ATSC


QAM (Quadrature Amplitude Modulation) and ATSC (Advanced Television Systems Committee) are two digital standards that are responsible for receiving and decoding the digital signals that are sent by the TV stations and cable companies. The major difference between the two is the medium from which they obtain the signal. ATSC receives Over the Air (OTA) signals whereas QAM is used in decoding the signals from a cable line. This difference has major implications in how each operates and their individual characteristics.

Although they are often treated as separate standards much of QAM is still based on ATSC. QAM is simply a different modulation technique and does not have anything to do with the format of the information that is being transferred. For that, QAM still uses the format that was established by ATSC.

As QAM was designed for cable, it requires a much cleaner media compared to ATSC. It’s because QAM lacks the error correction capabilities that are very important to ATSC due to the huge number of interference sources and possible signal distortions that can occur when transmitting over the air. QAM is also able to maximize the use of the 6Mhz bandwidth that is identical to both. Since the medium it uses does not have as much noise as that of ATSC. It is able to squeeze more channels into the bandwidth without causing interference or signal loss.

Due to ATSC being developed first and over the air transmission being a necessity, ATSC is installed in all TV sets that are meant to receive digital TV signals. Although QAM has been rapidly appearing as standard in TV sets that were released after 2006, a lot of older and low end TV sets still lack the ability to tune QAM. This is not a major issue though as most cable providers have a set top box along with their package that would decode the QAM signals that are being sent across the cable. The situation is improving though and it is simply a matter of time before QAM comes as standard in all HDTV sets.


1. ATSC is a digital standard for OTA while QAM is a digital standard for cable

2. QAM for digital TV is still largely based on ATSC

3. QAM needs a much cleaner signal medium compared to ATSC

4. QAM has double the bandwidth compared to ATSC

5. More TV sets are able to decode ATSC than QAM

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