Over-the-Air Digital Television (OTA DTv)

DIGITAL COMPARED TO ANALOG BROADCAST
Over-the-Air (OTA) digital television (DTv) requires a stronger signal than analog TV. Additionally, most DTv broadcast are in the UHF frequency band instead of the VHF band. UHF signals are higher in frequency and do not pass through or around objects as well as VHF signals. Also, over-the-air transmission and cable losses are greater at UHF frequencies. Antennas that picked up analog TV signals will also pick up digital TV signals, if the signal is strong enough.

A digital television's picture and sound quality are either 100%, or nothing. There are rare instances the signal power is just strong enough to decode, but fades in and out enough to pixelate the picture and/or garble the sound. This situation changes with atmospheric conditions and only last seconds to hours, then the signal is either good or gone. Analog TV processed weaker signals, the weaker the signal the more noise (snow) in the picture.

Digital TV broadcast are in high or standard definition (see Digital Televisions below). Cable and satellite operators often compress local broadcast channels before re-broadcasting. The compression reduces picture quality compared to over-the-air broadcast. Compressing signals opens up more bandwidth and allows providers to squeeze in more channels nobody watches.

Analog TV broadcast in the United States ended June 12^th (Friday), 2009. Since the introduction of digital TV, the number of over-the-air network channels has dramatically increased.

DIGITAL AND ANALOG CHANNELS
The old analog TV channels were the same as their broadcast Radio Frequency (RF) channel, one network per channel. Digital TV can broadcast multiple channels (in 1 RF channel) and uses 2 types of channels, the TV channel (also called Virtual channel) displayed on the TV, and the broadcast RF channel. A stations's TV channel may or may not be the same as it's RF channel. Most analog stations changed their RF channel (and most VHF stations moved to UHF) for DTv, but were allowed to keep their old analog channel identification as their TV or Virtual channel. Stations that signed-on the air after the transition to digital usually have the same TV and RF channel.

Analog Channel	Digital Channel
TV = RF channel	TV (Virtual) channel, - displayed on television. - multiple sub-channels. RF broadcast channel. VHF or UHF frequency band.

Sub-channels
Digital Channel numbers are the virtual TV channel, then a dot or dash, then sub-channel number (e.g. 6.3 or 6-3). Television channel 6.3 is virtual TV channel 6, sub-channel 3. The number of sub-channels varies from 1 to 7 or more.

The Federal Communications Commission (FCC) identifies a TV station's transmission (RF channel) by a callsign. Callsigns that start with a W _ _ _ are stations east of the Mississippi River, callsigns that start with a K _ _ _ are west of the river. Some stations have a callsign that includes a dash (-) followed by a 1 or 2 digit suffix (W or K _ _ _-DT). Sometimes the suffix reflects station service class, sometimes virtual channel number.

Callsign Suffix / Service

Suffix	Description	Service
DT	Digital TV	Full Power
TV	Television	Full Power
CA	Class A	Class A (Low Power)
CD	Class A Digital
D	Digital
LD	Low Power Digital	Low Power
LP	Low Power	Low Power

Broadcast Power (ERP)

Service	UHF	VHF
Full Power	≤ 1000 kW	≤ 185 kW
Class A	≤ 15 kW	≤ 3 kW
Low Power	≤ 15 kW	≤ 3 kW

A Class A station has Primary
status over low power stations.
Exact power limits vary by region.
ERP - Effective Radiated Power.
kW - kilowatts (1000 Watts).

FCC Service Class

Class	Description	Power
DT	Digital TV	Full Power
DC	Digital Class A Television	Low Power
DD	Distributed Digital Television	Low to Full Power
LD	Digital Low Power TV	Low Power
TX	Low Power TV and Translator	Low Power
DX	Auxiliary (backup) Facilities	Low to Full Power
LM	Land Mobile Use of TV Channel
DS	Digital Special Temporary Authority

DIGITAL TELEVISION
Almost all television's manufactured since 2007 have a built-in digital tuner, or more specifically an ATSC tuner, for receiving over-the-air TV. Some digital televisions do not use a low noise receiver (common in analog TV's and digital converters), and may not get some weaker signals. One reason not to use a low noise receiver is to cut cost, another is satellite and cable TV does not (usually) require a low noise receiver.

Most digital televisions can process both digital and analog signals (ATSC and NTSC), allowing the television to display analog DVD's, VCR's, and older video games.

Analog (NTSC) Televisions require a Digital Converter Box to receive OTA DTv. Most converters are also recorders. The antenna coax cable plugs into the converter box, the box is then connected with a coax cable to the televisions' Antenna Input. Some converters can also connect to the television with video, VGA, HDMI, or YPbPr cable sets for better picture and audio quality.

Computers, Laptops, Tablets, and Smart Phones require a DTv tuner to receive TV broadcast. The coax cable from your TV antenna plugs into the DTv tuner, the tuner connects to your computer or network router / switch. You may need to download a media/TV app for your devices if you don't already have one. Some DTv tuners have 2 receivers (2 tuners) for receiving 2 different TV channels simultaneously and available on your network.

Standard and High Definition
Over-the-air digital television can broadcast sub channels in high definition HDTV (720p, 1080i, 1080p), or standard definition (480i, 480p) resolution. The number is resolution in pixels per inch. The letter " p " stands for Progressive, picture lines are displayed one after the other. The letter " i " stands for Interlaced, odd picture lines displayed then even lines. High definition uses a wide screen aspect ratio of 16:9, or a square ratio of 1:1. Standard definition uses a ratio of 1:1, 4:3, or 16:9. The frame rate in North America is 23.976, 24, 29.97, 30, 59.94, and 60 frames per second (fps). The old analog TV system displayed an interlaced (i) picture, had an aspect ratio of 4:3, and a frame rate of 30 fps. Most Hollywood movies run at 24 fps.

The ATSC Digital TV Standards include HDTV, SDTV, data broadcasting, multichannel surround sound audio, and satellite direct-to-home broadcasting.

Definition	Resolution H x W (PPI)	Aspect Ratio	Frame Rate
High Definition (HDTV)	1080p	1080 x 1920	16:9 1:1	24 fps⁽¹⁾ 30 fps⁽²⁾
1080i	30 fps⁽²⁾
720p	720 x 1280	24 fps⁽¹⁾ 30 fps⁽²⁾ 60 fps⁽³⁾
Standard Definition (SDTV)	480p	480 x 704	16:9 4:3	24 fps⁽¹⁾ 30 fps⁽²⁾ 60 fps⁽³⁾
480 x 640	4:3 1:1
480i	480 x 704	16:9 4:3	30 fps⁽²⁾
480 x 640	4:3 1:1

Frame Rate
(1) (2) (3)	24 or 23.976 30 or 29.97 60 or 59.94	fps fps fps

Ultra High Definition (UHD) / 4k resolution (next-Gen TV)
Stations will continue to broadcast using the current standard (ATSC 1.0), but will have the option to simulcast on another frequency an Ultra High Definition signal (ATSC 3.0). The UHD signal will have higher resolution (3840 x 2160), great for extremely large screens, but of little value to small and moderate size screens. UHD will also have high dynamic range which changes colors faster for a better picture, and a maximum frame rate of 120 fps.. Additionally, UHD will have better reception by using new techniques that allow for a lower signal-to-noise ratio. UHD may catch on, or may go by the way of quadrophonic FM radio.

Receiver Signal Levels
Signal power is commonly measured in dBm - decibels above or below 1 milliwatt (mW). Television receivers will process signals from about 316 µW (microwatts) = -5 dBm to about 0.0003 µW = -65 dBm. A -65 dBm signal should come-in good for a short cable run to a single television, but may be too weak for long cable runs or signal splitters unless a preamp or booster amp is used.

A television's required minimum signal depends on the receiver sensitivity and local conditions (electronic noise pollution). Minimum signal can vary from as high as -55 dBm for a TV with poor sensitivity in a noisy environment, to as low as -75 dBm for a TV with good sensitivity in a low or no noise environment. Most televisions and conditions will require a signal level of at least -65 dBm.

Sensitivity depends on receiver Noise Figure (NF), a measure of the receiver's noise, and the minimum signal-to-noise (S/N) ratio required. Television receivers typically have a noise figure of 10 dB, but it can be as low as 6 or 8 dB, to as high as 20 dB. A minimum S/N of 30 dB is required in most cases due to interference from other signals, multi-path, and electronic noise.

Another factor is background noise, also called thermal or kTB noise, and is based on receiver noise bandwidth (6 MHz for an RF channel), and temperature. Temperature has a minor effect, and it is standard practice to use 300°K (80°F / 27°C), or 290°K (62°F / 17°C) for calculations. Noise is random with an average deviation of about ± 5 to ± 10 dB from the average level. Peak noise will be greater.

Minimum Signal in Watts = kTB (NF) (S/N)

k = Boltzmann's Constant = 1.380 622 x 10^-23 Watt sec / °K.
T = Temperature in Degrees Kelvin (°K).
B = Receiver Noise Bandwidth in Hertz (Hz).

NF - Noise Figure (ratio).
S/N - Minimum Signal-to-Noise (ratio).

Estimate TV Minimum Signal
Temperature (T):
Noise Bandwidth (B):
Noise Figure (NF):		dB
Signal-to-Noise (S/N):		dB
Background Noise (kTB) Noise out of Receiver (kTB NF) Minimum TV Signal (dBm)

°C = Degrees Celsius
°F = Degrees Fahrerhigh
°K = Degrees Kelvin

In the laboratory a television could receive a signal as low as -83 dBm, using a receiver with a noise figure (NF) of 8 dB, and a signal-to-noise (S/N) ratio of 15 dB. Noise would have to be minimized by protecting the TV receiver from outside interference by cabling a single signal (1 RF channel) from a lab signal generator directly to the TV receiver.

Some RF Broadcast Channels will be Changing between 2017 - 2020+
Some DTv stations will be changing channels over a 3+ year period, until about 2020 and probably longer. The FCC, at the direction of Congress in 2012, is re-allocating spectrum, forcing around 1000 TV stations to change RF Broadcast Channels. There are about 8000 TV stations in the U.S. and its' territories.

Stations	Percent	Change
145	1.8%	Go off-the-air
13	0.2%	Move to VHF-Hi
17	0.2%	Move to VHF-Lo
1000	12.5%	Change UHF Channel

Picking Up TV Signals
A little planning can insure the best results possible (see TV Tower Locator and Reception Practices). Understanding Reception Factors is important when dealing with distant towers, marginal or spread out signals, hilly or mountainous terrain, ground clutter, and indoor antennas. Antenna selection depends on frequency bands, antenna gain (Calculate Antenna Gain Needed), and coverage needed. Cable loss depends on cable length(s) and connections. Outside Antennas should be properly grounded for best reception and safety.

Digital TV Reception Factors Tower Locator Antennas Amplifiers Cables Installation Frequency Networks News Blog Over-the-Air Digital Television (OTA DTv) otadtv.com
Contact Privacy Policy, Terms and Conditions	© Copyright 2017, All Rights Reserved