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OTA DTv Reception Factors

Basic steps to estimate signal strength to your television and get the best reception. Account for cable and signal splitter losses, antenna signal based on gain, antenna height loss, and potential ground losses.

Factors

Basic Steps
1.) Find Broadcast Towers.
Signal Strength at Antenna, Angle, Band.
2.) Estimate Home Antenna Gain.
3.) Estimate Ground Losses.
4.) Calculate Cable / Splitter Loss.
5.) Calculate Signal to TV's.
Signal Strength Calculator
Planning Steps
reception factors
1.) FIND BROADCAST TOWERS
Tower Locator

The receive signal strength will vary from around -20 dBm for a full power broadcast within a few miles to -65 dBm or less for distant towers.

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2.) ESTIMATE ANTENNA GAIN

The larger the antenna the higher the gain. Account for antenna gain loss for signals near the beam edge (gain down by -3 dB at the edge). Note advertised gains are for the highest frequency (highest RF channel), gain will be less for lower frequencies, up to several dB. See Antenna Loss Factors.

ANTENNA Gain
dBi
Beamwidth
Degrees
Low Gain (Indoor) 2 - 4 ≤ 120°
High Gain (Attic / Outside) 5 - 10 60° - 90°
Very High Gain (Outside) 11 - 15+ ≈ 30°

3.) ESTIMATE GROUND LOSSES

Antenna Height Loss
Antenna's lower than 30 feet Above Ground Level (AGL) will introduce a signal loss from ground reflections. Loss varies from a few dB for high antenna's to around -10 dB for lower antenna's. See Signal Factors.

Clutter Loss
Trees, structures and hills relatively close to the home antenna will introduce a loss, from a few dB to completely block a signal. Attic antenna's have at least a -3 dB loss from the roof. Indoor antenna signals will be reduced by walls and other obstructions from several dB to 10's of dB's. In most cases clutter loss can only be roughly estimated. See Signal Factors.

4.) CALCULATE CABLE LOSS
Cable Loss Factors
  • Cable Length.
  • Signal Splitters.
  • Connectors and Adapters.
  • RF Channel ((Signal Frequency).

Cable length and signal splitters account for the most loss. Connectors, adapters, and higher frequency signals add some loss. There's enough difference between VHF and UHF signals they should be accounted for separately. See below calculator.

5.) CALCULATE SIGNAL TO TELEVISION

Television receivers require a minimum signal level greater than ≈ -65 dBm, but it can be as low as -75 dBm to as high as -50 dBm. See TV Minimum Signal.

Estimate signal to TV:

Signal to Antenna dBm
+ Antenna Gain dBi
- Ground Losses dB
- Cabling Loss dB

= Signal to TV dBm

Estimate Signal to Television
RF Channel:
Signal to Antenna: dBm
Antenna Gain:
Antenna Height:
Area
Clutter Loss: dB
Coax Cable Type:
Cable Length:
Signal Splitters: 2 Ports , 3 Ports
4 Ports , 8 Ports
Connectors: Ground Block, barrels etc.
Twin-lead/Coax Adapters

RF Channel
Frequency / Band

Antenna Gain
- Antenna Height Loss
-Clutter Loss
-Cable Loss
-Splitters Loss
-Connectors loss

= System Gain / Loss
+ Signal to Antenna

= TV SIGNAL
Strength Bars

  • AGL -- Above Ground Level
  • Antenna Height ≥ 1.5 ft ( 0.5 m).
  • TV minimum signal: -65 dBm.
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Your location and antenna are the main factors that determine the number of channels you can get. A preamplifier can be used to improve weak signals. A booster amplifier can be used to overcome long cable runs. A distribution amp can be used to overcome signal splitting losses. See Amplifiers

Standard Practices

The ideal scenario is an antenna 30 feet or more above the ground, pointed directly at the tower antenna, in tower antenna main beam, with flat open terrain and a clear line-of-sight.

ANTENNA
Placement
  • As high as possible.
  • Clear of clutter in tower directions.
  • Pointed in direction of broadcast towers.
Frequency
Bands
  • Most broadcast are in the UHF band.
    In some cases a UHF antenna works for VHF signals.
  • Use a VHF / UHF antenna to get all bands.
Weak
Signals
  • Use a high gain antenna.
  • Install an antenna pre-amp.
Distant and
Spread Out
Headings
  • Use 2 or 3 antennas.
  • Use an Omni antenna (360° coverage).
  • Rotor antenna (high gain and 360°).
CABLING
Coax
  • RG-6 coax cable (F-type connectors).
    Can use RG-11 or RG-59 coax cable.
  • Cable runs as short as possible.
  • Use quad shield coax for outside runs.
Connectors
  • Make sure all connectors are tight.
  • Check outside connectors for corrosion.
  • Outside connectors covered with a
    rubber weather boot or electrical tape.
  • Unused ports capped with a 75 Ω load.
Long Cable Runs
  • Use a Booster amp.
Multiple Splitters
  • Use a Distribution amp.

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Basic Steps for Reception