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How to Use Hardline on VHF

Hardline has lower loss than other types of coaxial cable, making it an excellent choice to connect a transmitter to an antenna mounted on a building or tower. Lower loss in the cable means a stronger signal at the distant receiver. VHF frequencies range from 30 to 300 MHz. Hardline cable ranges from 1/4 inch to 1 5/8 inches in diameter. Using hardline requires calculating which diameter is needed at your operating frequency to achieve the receive signal level (RSL) needed to exceed the threshold of the receiver to meet the reliability requirements of your particular application.

Things You'll Need

Specification sheets for hardline cable
Calculation sheet for the VHF path

Instructions

- 1
  
  Hardline coaxial cable ranges in diameter from 1/4 inch to 1 5/8 inches.
  
  Measure the distance from the transmitter to the antenna at one end of the VHF path and from the antenna to the receiver at the other end. Account for all bends made along the routing.
- 2
  
  Several types of transmitters use hardline coaxial cable for lower loss.
  
  Recalculate your overall pass loss using the figures for 1/4-inch hardline from the specification sheet at your operating frequency and the data from your original path calculation sheet. Add your transmitter power, subtract the hardline loss, add the transmit antenna gain, subtract the free space loss, add the distant receiver antenna gain and subtract the distant hardline loss. Compare the resulting figure to the threshold specifications of your receiver. The difference between the final signal level and the threshold of the receiver is called the "fade margin."
- 3
  Compare the fade margin to the specifications of the project. If it meets the specifications, use the 1/4-inch hardline. If not, substitute the hardline loss statistics for larger-diameter cables into the path loss calculations until you find a diameter that meets or exceeds the requirements. If 1-5/8-inch hardline still does not meet the specifications, improve the path by increasing transmitter power or using higher-gain antennas, then do the hardline calculations again.

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