Introduction:
The concept of receiving ATSC 3.0 signals through an embedded antenna inside budget smartphones is fraught with challenges. This article extends the conversation, specifically scrutinizing the idea of earphone-embedded antennas, akin to FM reception, and explicates why this approach significantly compromises the reception of ATSC 3.0 signals, thereby complicating the system further.
I. Signal Nature and Modulation Techniques
- FM (Frequency Modulation): An analogue system where audio is modulated through carrier wave frequency variations. FM is robust against amplitude noise, benefiting from noise reduction strategies like pre-emphasis/de-emphasis and the capture effect, enhancing the signal-to-noise ratio (SNR).
- ATSC 3.0: A digital standard employing sophisticated modulation schemes such as OFDM, transmitting extensive data. Despite advanced error correction techniques, ATSC 3.0 is prone to the “cliff effect,“ leading to abrupt signal quality deterioration when noise surpasses a certain threshold, in stark contrast to the gradual degradation in FM.
II. Bandwidth, Frequency, and Antenna Design
- FM: Functions within the VHF band (88 – 108 MHz), are characterized by narrow bandwidth (200 KHz) and lower frequencies that are conducive to simpler antenna designs and reduced specific interference susceptibility.
- ATSC 3.0: Requires sophisticated antenna designs due to its significantly broader bandwidth (8 MHz vs 200 KHz that of FM) and higher frequencies, which amplify noise susceptibility, rendering earphone-embedded antennas unsuitable.
III. Pre-emphasis and De-emphasis in FM
FM leverages pre-emphasis and de-emphasis techniques to improve the signal-to-noise ratio for high-frequency components:
