|DIGITAL TELEVISION (DTV)|
Digital television (DTV) requires a stronger signal than analog TV. Additionally, most DTV transmitters are in the Ultra High Frequency UHF band (channels 14 - 51). These signals are higher in frequency and are Line-of-Sight -- do not pass through or around objects as signals in the Very High Frequency VHF band (channels 2 - 13). Also, over-the-air transmission losses are greater at UHF frequencies. Antennas that picked up analog TV signals will also pick up DTV (or HDTV - High Definition TV) signals, if the signal is strong enough.
DTV, RF and Analog Channels
The old analog TV channel identification used the transmit frequency channel number, usually called the Radio Frequency RF channel, DTV does not (always). A station's identifing DTV channel may or may not correspond to it's RF transmit channel. Most analog TV stations changed their RF channel for DTV, but were allowed to keep their old analog channel identification as their DTV or Virtual Channel identification. Because multiple programs (stations) can be broadcast within one RF channel, DTV identifications are virtual channel with a dot or dash for sub-channel (e.g. 69.1 or 69-1). Also see St Louis DTV Stations.
|May or May Not
be RF Channel
|2 - 13||VHF|
|14 - 69||UHF|
Callsign Suffixes (Show / Hide...)
Over-the-Air (OTH) digital television can broadcast sub channels in high definition (720p or 1080i) or standard definition (480i) resolution. Some sub-channels are audio only. The "p" in the resolution stands for Progressive, picture lines are displayed one after the other. An "i" stands for Interlaced, odd picture lines displayed then even lines.
Cable and satellite operators often compress local broadcast channels before re-broadcasting. Compressing signals opens up more bandwidth and allows for more channels nobody watches. The compression reduces picture quality compared to over-the-air broadcast.
Almost all TV's manufactured after 2006 have a built-in digital tuner, or more specifically an ATSC tuner, for receiving over-the-air TV broadcast. HD TV's that do not have an ATSC tuner, and older picture tube TV's, require a Digital Converter Box. The antenna signal plugs into the converter box, which is connected to the TV RF antenna input using coax, or connected using an HDMI cable, or VGA / audio cables, or RCA video (S video) / audio cables, or YPbPr / audio cables. The box formats the signal to the analog NTSC standard.
|ATSC||-||Digital TV standard|
|NTSC||-||Analog TV standard|
ATSC - Advanced Television System Committee
NTSC - National Television System Committee
|IMPROVE SIGNAL RECEPTION|
Replace all flat twin-lead (300 ohm) and RG-59 coax cables with RG-6 coax (75 ohm) cables. TV coax cables use F-type connectors, F type male connectors on the cable, and female F type connectors on the antenna and TV. Check all outside cable connections for corrosion, replace if necessary. Cable runs should be as short as possible.
All cables cause a signal loss, the longer the cable the greater the loss. Additionally, the higher the frequency, the higher the RF channel number, the greater the loss. Cable loss is measured in decibels (-dB's). Decibels are additive, the loss of two connected cables is the sum of the loss of each cable (add the dB's).
Cable Loss Calculator
RG-6 Coax Cable
Signal power (dBm) drops directly by cable loss dB's.
dBm = decibels with respect to one milliwatt. A negative dBm is dB's below a milliwatt, a positive dBm is dB's above a milliwatt, 0 dBm = 1 mW.
Keep the number of signal splitters to a minimum. A two outputs (2 port) signal splitter cuts the signal in half, introducing a loss of about -3.5 dB for channel 2, and -4 dB for channel 69. A four outputs (4 port) splitter has a loss of about -7 to -8 dB. Adding a 2 port splitter is equivalent to adding about 70 feet of cable, a 4 port splitter is like adding about 140 feet of cable.
SYSTEM LOSS CALCULATOR (Show / Hide...)
Long cable runs and signal splitters may require installing a booster amplifier, increases signal 20 or 30 dB. A booster-amp will not improve a weak antenna signal, because it amplifies signal and noise, but it will allow for longer cable runs and more splitters. Most booster amps have an adjustable gain, some are fixed gain, all are powered by house current (110 Vac).
Pre-amps are low noise amplifiers (amplifies signal but not noise) that mount to an indoor or outdoor antenna to improve a weak signal, up to +20 or +25 dB. Signal improvement is the preamp gain minus the Noise Figure, the lower the noise figure the better. The amplifier mounts to the antenna, or as close as possible, for maximum performance. The antenna preamp works with a separate power unit inside the home that supplies power to the amp through the coax cable (center conductor). Most preamps cover the VHF and UHF bands, many have an adjustable gain, most plug into a standard power outlet (110 Vac), some are powered from a USB connection.
|Bands:||VHF / UHF|
|Gain:||+20 to +25 dB or more
Adjustable or Fixed Gain
|Noise Figure:||2 to 4 dB (lower is better)|
|Power Source:||110 Vac or USB|
An FM Trap filters out the commercial FM radio band which is between RF channels 6 and 7. The filter may be needed if an FM signal is strong enough to overpower the preamp or reduce it's automatic gain control. Some traps reduce RF channel 6 reception.
UHF antennas (RF channels 14 - 69) are much smaller than VHF antennas (RF channels 2 - 13) because the wavelengths are shorter. Antenna size is proportional to wavelength, the higher the frequency, the higher the RF channel, the shorter the wavelength and the smaller the antenna. UHF wavelengths vary from about 1 to 2 feet, VHF wavelengths vary from about 5 to 17 feet. Also see Electromagnetic Waves
The antenna should be located as high as possible and have a clear line-of-sight (no hills, structures, trees, etc.) to the broadcast towers. The higher the receiving antenna is above the ground and above ground clutter the greater the signal density.
OUTSIDE TV ANTENNAS
Federal law prohibits restrictions (by governments, community associations, and other entities) that impair the installation, maintenance or use of antennas used to receive video programming. Masts higher than 12 feet above the roofline may be subject to local restrictions. See FCC OTA Reception Devices Rule.
Television antennas come in 3 basic frequency bands, VHF-Lo, VHF-Hi, and UHF. Most antennas are UHF only, some antennas combine the entire VHF and UHF bands (VHF/UHF), and some combine the VHF-Hi and UHF bands (VHF-Hi/UHF).
|VHF-Lo||2 - 6||54 - 88 MHz|
|VHF-Hi||7 - 13||174 - 216 MHz|
|UHF||14 - 69||470 - 806 MHz|
ANTENNA GAIN: The larger the antenna, the more signal captured, the higher the antenna gain, and the more narrow the beam. Reception range doubles for a gain increase of +6 dB, and antenna size will quadruple. Antenna gain is expressed in dBi or dBD. Gain expressed in dB is usually really dBD, makes gain look 2 dB higher. Most antennas have a positive gain, some smaller indoor antennas have a negative gain. Outdoor antenna gains vary from a few dBi to about +20 dBi at the high end. Most outside antennas have a gain of around +10 dBi.
ANTENNA POINTING ANGLE
Most antennas are directional and must be pointed toward the broadcast tower for best reception. Most UHF antennas have a relatively wide beam ((best reception angles), but are less forgiving (more narrow beam) than VHF antennas. Adjusting an antenna's pointing angle may help pull in weak signals.
* Latitude and Longitude in decimal degrees.
Deg/Min/Sec to Decimal Degrees Calculator (Show / Hide...)
Receive antenna location coordinates (latitude / longitude) can be obtained from most GPS's and smartphones, or see itouchmap.com.
(1) -- The Signal Level (dBm and percent) calculation is an estimate of power delivered to an antenna that is 30 feet above the ground, in an open field, and has a clear line-of-sight to the broadcast tower. The calculation does not account for broadcast tower elevation, antenna height, beam direction, or radio horizon.
Typical variables that effect signal power from a receive antenna (output connector) include, but not limited to;
|Beam Loss:||0 to -10 dB|
|Gain:||-3 to +20 dB|
|Beam Loss:||0 to -10 dB|
|Terrain / Ground Loss:||0 to -12 dB|
|Clutter / Obstructions:||-1 dB to No Signal|
|Attic Mount:||-3 dB to No Signal|
|Outside the Broadcast
Beam loss occurs when the transmit antenna beam and receive antenna beam are not aligned. Ground loss results from reflections off the ground. Attic mount loss of -3 dB is for a 3/4 inch plywood roof with roofing paper and a single layer of 3 tab asphalt shingles. Metal backed insulation on the attic roof or walls and metal exhaust vents / pipes block signals. Broadcast tower elevation and height determines radio horizon, usually limited to less than 65 miles. Receive antennas beyond the broadcast radio horizon must be mounted higher than usual above the ground, be pointed (fixed or using a rotor) for maximum signal, and usually need a high gain antenna with a preamp.
Also see DTV Reception Maps (dtv.gov/maps).
|TELEVISION RECEIVER SIGNAL|
Digital television receivers will process signals from about -5 dBm (strong) to about -65 dBm (weak).
|Calculate Signal Level to TV|
|Signal to Antenna:||dBm|
|4 Port Splitters:|
|2 Port Splitters:|
|Adapters (75/300 ohm):|
Signal from Antenna
In almost all cases there is either a good picture and sound, or there is not. There is no difference in picture or sound quality between a good and weak signal. There are some relatively rare instances where the signal power is just strong enough to demodulate and decode, but fades in and out enough to pixelate the picture.
INDOOR PASSIVE ANTENNAS
Wide Beam ≈ ≥ 60° / Gain: ≈ -3 to +4 dBi
INDOOR ACTIVE PREAMP-ANTENNAS
Wide Beam ≈ ≥ 60° / Gain: ≈20 dBi
OUTDOOR ANTENNAS / MODERATE SIGNALS
Beam: ≈ 60° / Gain: ≈ 5 to 9 dBi
Some installations have an additional ground rod close to the antenna for a little extra safety. The antenna ground wire can be insulated or uninsulated, run inside or outside the home, and be tied into the home power service grounding electrode system near the power meter or fuze / breaker box. The coax Drip Loop allows rain to collect and fall (drip) off the bottom of the loop instead of collecting at the conduit into the home.
A signal that is too strong can overwhelm (saturate) a TV receiver, causing signal distortion (cannot decode signal). An attenuator can reduce the signal to an acceptable level. Some attenuators have a fixed reduction, some are adjustable.
Older antennas and TV's use a 300 ohm twin-lead connection. In these cases a coax to twin lead adapter (75 to 300 ohm) also called a balun (matching network, typically a ferrite transformer) is required to connect twin-lead to coax. An impedance matching transformer minimizes signal loss. An adapter works both ways, signals go from coax to twin-lead or twin-lead to coax.
ADAPTER SIGNAL LOSS
-0.2 dB for channel 2
-1 dB for channel 14
-2 dB for channel 69
Type F male/female adapters have a typical loss of -0.5 dB.
RF CHANNEL FREQUENCIES
Each RF channel is 6 MHz wide.
The Best of the Essentials
DTV Antennas and Accessories
Outdoor Antennas -- Indoor Antennas -- Amplifiers -- Signal Splitters -- Coax -- Installation Hardware