Broadcast TV Reception
PAGE CONTENTS --
Cabling Loss |
Antenna Gain |
TV Signal |
The following basic steps can be used for new installations to select an antenna type and determine cable layout. The steps can also be used for existing installations for antenna pointing adjustments and estimating signal levels to the televisions.
||Find Broadcast Towers.
|| Calculate Cable Loss.
|Calculate Antenna Gain needed,
or estimate existing antenna gain.
||Calculate Signal to TV's.
||Install an amplifier if needed.
1.) BROADCAST TOWERS
Use the TV Tower Locator to find stations in your area. From the results note the signal angles for antenna pointing, look for terrain interference, note frequency band for selecting an antenna, and note signal levels (dBm). Concentrate on the weakest and longest range signals of interest. Be familiar with Reception Factors and look for circumstances that could cause a signal to be weaker than calculated or does not come in at all.
2.) CABLE SIGNAL LOSS
Cable loss varies with frequency, the higher the frequency (the higher the RF channel), the greater the loss. In most cases using the average of a frequency band (VHF-Lo, VHF-Hi, UHF) to calculate loss is close enough. Loss can also be calculated for a specific RF channel. Cable loss also depends on cable length and the number and type (output ports) of signal splitters. Cable connectors and adapters introduce a small loss. The calculators below compute cable loss for RG-6 coax cables, the preferred cable for broadcast TV reception. See TV Coax Cables, Splitters, and Connectors for more details.
3a.) ANTENNA GAIN - new installations
A negative gain indicates any antenna will work.
Antenna gain needed can be approximated by subtracting cable loss (dB) from broadcast signal (dBm). If the result (signal - loss) is greater than the minimum signal required by the TV (typically -65 dBm), any antenna will work. If the result is less than minimum, the difference is the antenna gain needed.
Gain is an estimate and should be padded 3 to 6 dB.
3b.) ANTENNA GAIN - existing installations
Estimate your antenna gain for use in signal to TV calculations (step 4). Antenna gains average from around 3 dBi for indoor antennas, to 8 dBi for indoor/outdoor antennas, to 13 dBi for large outdoor antennas. An alternative is to use 0 dBi gain as a conservative and easy reference.
|Large Outdoor Antenna
4.) ESTIMATE SIGNAL TO TELEVISION
Signal power delivered to the television equals broadcast signal available to the receive antenna plus antenna gain, minus cabling loss.
||Signal to TV
A good signal is from 8% to 50% (-60 to -35 dBm).
A strong signal is greater than 50% (-35 to -5 dBm).
A preamplifier can be used to improve weak broadcast signals. A distribution or booster amplifier should be used to overcome cable loss.
SUMMARY and TIPS
- 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°).
- RG-6 coax cable (F-type connectors).
- Cable runs as short as possible.
- Make sure all connectors are tight.
- Check outside connectors for corrosion.
- Outside connectors covered with a
rubber weather boot or electrical tape.
- Unused ports covered with a 75 ohm load.
- Long cable runs, multiple Signal Splitters
- Use a distribution / booster amp.