You Are Here:

Antenna Cable Length Considerations

When designing an antenna system, cable length must be taken into consideration, as it not only impacts the signal strength, but also can cause a signal delay that needs to be compensated for.

Signal Strength

Calculate the maximum allowable cable length, using the following antenna and cable data:

  • Antenna Model 8230: 40 dB (antenna) – (cable loss) + 20 dB (Preamp if used) – (1dB/surge protector) – (.5dB/connector) = XXdB
  • Antenna Model 8225S: 33 dB (antenna) – (cable loss) + 20 dB (Preamp if used) – (1dB/surge protector) – (.5dB/connector) = XXdB
  • Antenna Model 8225: 30 dB (antenna) – (cable loss) + 20 dB (Preamp if used) – (1dB/surge protector) – (.5dB/connector) = XXdB
  • Antenna Model ANT35: 35 dB (antenna) – (cable loss) + 20 dB (Preamp if used) – (1dB/surge protector) – (.5dB/connector) = XXdB

Cable loss:

  • Andrews Heliax 5/8 in: 2.1 dB/100 ft or 0.6 db/10m
  • Andrews Heliax ½ in: 2.7 dB/100ft or 0.8 db/10 m
  • LMR-400: 5.5 dB/100 ft or 1.7 db/10 m
  • RG-213 (ex: Belden 8267): 10 db/100ft or 3.5 db/10 m
  • RG-58: 27.6 dB/100 ft or 9.2 db/10 m

Where XX db = minimum gain required at the receiver.

Notes:

  1. Optimal location of a preamp if necessary is between the 10-20 dB loss location.
  2. Andrews Heliax requires special connectors and training to install.

Signal Delay

Cable delays and other latencies can be compensated for by offsetting the system's on-time point using an Offset value specific to the antenna cable length. The API call is: TSYNC_GR_setOffset (see Factory Driver Guide), and it can be adjusted by ±500 ms

Under typical conditions, the expected cable and amplifier delays are negligible. You can calculate the delay based on the manufacture’s specifications. The range of the cable delay is ±50,000,000 nanoseconds. The default value is 0 nanoseconds and the resolution is 1 nanosecond. The following formula is used to calculate the cable delay:

  • D = ( L * C ) / V

Where:

  • D = Cable delay in nanoseconds
  • L = Cable length in feet
  • C = Constant derived from velocity of light: 1.016
  • V = Nominal velocity of propagation expressed as decimal, i.e. %66 = 0.66 Value is provided by cable manufacturer.

When using LMR- 400 or an equivalent coax cable, this formula equates to approximately 1.2 nanoseconds of delay per every foot of cable. To calculate the Offset value (cable delay), multiply the length of the entire cable run by “1.2” and then enter this value into the Offset field.

Examples of LMR–400 coax cable delays:

100 feet of cable = 120 nanoseconds of cable delay

200 feet of cable = 240 nanoseconds of cable delay

300 feet of cable = 360 nanoseconds of cable delay