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Over-the-Air (Free TV)
Digital Television Reception

OTA DTV Reception
Digital Television | Improve Reception | Antenna Selection | Receiver Signal Levels | Frequencies

DIGITAL TELEVISION (DTV)
Digital TV requires a stronger signal for reception compared to an analog TV set/signal. Additionally most DTV transmitters are in the Ultra High Frequency UHF band. UHF signals are Line-of-Sight and do not pass through or around objects as in the Very High Frequency VHF band. Also propagation and atmospheric losses are greater at UHF frequencies. Antennas that picked up analog TV signals will also pick up DTV signals if the signal is strong enough.

DTV Virtual Channel vs RF Channel
The old analog TV stations identified themselves by channel frequency, DTV does not. A station's DTV channel may or may not correspond to the transmitted frequency channel, referred to as Radio Frequency RF channel. Most broadcasters that transmitted analog on a VHF channel (RF 2 - 13) moved to the UHF band (RF 14 - 69) for DTV, and kept the old channel designation as it's DTV or Virtual channel designation.

Because multiple programs (stations) can be broadcast within one RF channel, DTV designations are virtual channel with a dot or dash for sub-channel (69.1 or 69-1). Also see St Louis DTV Stations.
Transmit Tower 4-bowtie dipole DTV - Analog Carrier / Digital Modulation

coax and twin lead cables
IMPROVE SIGNAL RECEPTION
CABLES: All twin-lead (300 ohm) cables should be replaced with RG-6 coax (75 ohm) cables. Double or triple shielded RG-6 should be used in noisy electronic environments; transmitters, high power lines, transformers or motors. Cable runs should be as short as possible. Long cable runs and/or power splitters may require an antenna pre-amp. A 2-port (1 input to 2 outputs) power splitter (loss) is equivalent to adding about 55 feet of cable.

RG-6 Cable Loss for DTV UHF Band
Cable Length (feet) 1 ft 5 ft 10 ft 25 ft 50 ft 75 ft 100 ft
Range Loss (percent) -0.6% -3% -6% -15% -27% -38% -47%


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) is required when running coax. The adaptors use an impedance matching transformer making signal loss minimal.

ANTENNA ELEVATION: The antenna should be located as high as possible and clear of obstructions (hills, structures, trees, etc.). The higher the receiving antenna is above the ground level the greater the signal density. In some scenarios range could more than double or triple.

ANTENNA POINTING DIRECTION: DTV signals are in the UHF band and most UHF antennas are directional. A UHF antenna must be pointed in the direction of the DTV transmitter tower for best reception. A UHF receive antenna beam is relatively wide, but less forgiving than VHF antennas (RF channels 2 - 13).

PRE-AMP: Antenna pre amps amplify a weak signal, up to 20 - 25 dB (decibels). Pre amps are 2 piece devices. A small control box inside the home is connected to the antenna cable that connects to a small pre amp mounted on the antenna that connects directly to the antenna connector. The control box has a manual gain control and plugs into any power outlet (110 Vac). The control box supplies power to the antenna mounted pre amp through the coax cable center conductor.

HIGH GAIN ANTENNA: High gain antennas have narrow beams and may require a rotor to move the beam (rotate antenna) between stations with a wide angle separation.

SUMMARY
  • Use a UHF antenna since most DTV transmissions are in the UHF band.
    In many cases a UHF antenna will work for VHF transmissions (if any).
  • Replace 300 ohm twin-lead with RG-6 (75 ohm) coax cable.
  • Cable runs as short as possible.
  • Antenna as high as possible and clear of obstructions.
  • Antenna pointed in direction of DTV transmitter towers.
  • Install an antenna pre-amp.
  • Install a high gain antenna.



ANTENNA SELECTION
Antennas will pick up signals from all directions, best reception occurs in the main lobe or beam. UHF antennas are smaller and more directional, poor backside reception, compared to VHF antennas. VHF antennas are larger with wider (main) beams and larger side/back lobes compared to UHF antennas.

RADIO FREQUENCY (RF) BAND
Television antennas come in 3 basic configurations or frequency band sets; VHF, VHF/UHF, or UHF. Very few DTV transmitters are in the VHF band (RF channels 2 - 13).
Band RF Channels Frequency
VHF 2 - 13 54 - 216 MHz
VHF/UHF 2 - 69 54 - 216 MHz
470 - 806 MHz
UHF 14 - 69 470 - 806 MHz
ANTENNA GAIN
Higher gain antennas pick up weaker signals. To double the range (increase gain 6 dB) the antenna size increases over 4 times.
dBD = dBi + 2.15
dBi = dBD - 2.15
Common Antenna Types
The below listing includes 4 common and widely used antenna types; log-periodic, yagi, loop reflector and bowtie dipole reflector. Yagi and log-periodic antennas have good wind resistance. Bowtie dipole reflectors have good gain for size, dual loop reflectors have wide beams for gain. Gains (dBi), beam (azimuth or horizontal beamwidth) and ranges are approximated for comparison purposes and vary with model.

Outside factors that influence range include DTV transmitter power and antenna height, and receive antenna surrounding terrain and elevation. DTV transmitter power varies with station from a few kilowatts (kW) to 1000 kW ERP (Effective Radiated Power).
Indoor Antennas Outside Antennas
Vertical Profile with optional Pre-Amp
Horizontal Profile / Pre-Amp
Log-Periodic
+30 Mile Range
Gain:
Beam:
5 dBi (VHF), 8 dBi (UHF)
60° (VHF), 30° (UHF)
Single Loop
+25 Mile Range
Gain:
Beam:
5 dBi
130°
2 Dual Loops
+35 Mile Range
Gain:
Beam:
10 dBi
30°

Outside Antennas
2-Bay Bowtie
+35 Mile Range
Gain:
Beam:
10 dBi
45°
4-bay Bowtie
+45 Mile Range
Gain:
Beam:
12 dBi
25°
8-bay Bowtie
+65 Mile Range
Gain:
Beam:
15 dBi
10°
High Gain Yagi
+65 Mile Range
Gain:
Beam:
16 dBi
25°

RECEIVER SIGNAL LEVELS
Analog receivers require a minimum signal to noise ratio (S/N) of 10 - 15 dB, receive signal must be at least 10 - 15 dB (depends on receiver) above the noise floor. Digital (DTV) receivers require a S/N of 25 - 30 dB above the noise floor. The noise floor increases in noisy electronic environments; close proximity to transmitters, high power lines, transformers or motors, and atmospheric conditions.
DTV Receiver Signal Levels
BAD Marginal Moderate GOOD
Noise Low S/N 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
-84 -71 -65 -59 -53 -47 -41 -35 -29 -23 -17 -11 -5 dBm
-35 -22 -15 -10 -4 2 8 14 20 26 32 38 44 dBmV
0.02 0.08 0.15 0.3 0.6 1.2 2 5 10 19 39 77 154 mV

dBm = decibels with respect to 1 milliwatt
dBmV = decibels with respect to 1 millivolt
mV = millivolts

RF CHANNEL FREQUENCIES
Each Digital Television RF channel is 6 MHz wide, +/- 3 MHz of center frequency. Digital technology allows broadcasters to transmit multiple programs within the 6 MHz bandwidth.

UHF Band
Ultra High Frequency
300 - 1000 MHz

RF
Channel
Center
Frequency
MHz
Sub-
Band
MHz
14 473 470 - 476
15 479 476 - 482
16 485 482 - 488
17 491 488 - 494
18 497 494 - 500
19 503 500 - 506
20 509 506 - 512
21 515 512 - 518
22 521 518 - 524
23 527 524 - 530
24 533 530 - 536
25 539 536 - 542
26 545 542 - 548
27 551 548 - 554
28 557 554 - 560
29 563 560 - 566
30 569 566 - 572
31 575 572 - 578
32 581 578 - 584
RF
Channel
Center
Frequency
MHz
Sub-
Band
MHz
33 587 584 - 590
34 593 590 - 596
35 599 596 - 602
36 605 602 - 608
37 611 608 - 614
38 617 614 - 620
39 623 620 - 626
40 629 626 - 632
41 635 632 - 638
42 641 638 - 644
43 647 644 - 650
44 653 650 - 656
45 659 656 - 662
46 665 662 - 668
47 671 668 - 674
48 677 674 - 680
49 683 680 - 686
50 689 686 - 692
51 695 692 - 698
RF
Channel
Center
Frequency
MHz
Sub-
Band
MHz
52 701 698 - 704
53 707 704 - 710
54 713 710 - 716
55 719 716 - 722
56 725 722 - 728
57 731 728 - 734
58 737 734 - 740
59 743 740 - 746
60 749 746 - 752
61 755 752 - 758
62 761 758 - 764
63 767 764 - 770
64 773 770 - 776
65 779 776 - 782
66 785 782 - 788
67 791 788 - 794
68 797 794 - 800
69 803 800 - 806

Ch 37 reserved for radio astronomy.

VHF Band
Very High Frequency
30 - 300 MHz

Use Sub-
Band
MHz
Government and
Public Service
30 - 50
Amateur Radio 50 - 54
RF
Channel
Center
Frequency
MHz
Sub-
Band
MHz
2 57 54-60
3 63 60-66
4 69 66-72
Shared Use 72-76
5 79 76-82
6 85 82-88
FM Radio 88 - 108
Air Navigation 108 - 118
Aircraft Voice (AM) 118 - 138
Radar 138 - 144
Amateur 144 - 148
Police / Fire / Ambulance
and Business
148 - 164
Public Service 164 - 174
RF
Channel
Center
Frequency
MHz
Sub-
Band
MHz
7 177 174 - 180
8 183 180 - 186
9 189 186 - 192
10 195 192 - 198
11 201 198 - 204
12 207 204 - 210
13 213 210 - 216
Radar 216 - 225
Government 225 - 300


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