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Yunnan Nanyue Electric Power Equipment Co., Ltd.
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FAQ

How to Test a Transmission Line?
How to Test a Transmission Line?
 A transmission line carries a signal from a transmitter to an antenna. Ideally, all the power from the transmitter would reach the antenna. But some of the signal reflects back due to characteristics of the line. The size of the reflected signal is called the "voltage standing wave ration" (VSWR). A VSWR of 1.00:1 means a perfect transmission line no reflections. Higher rations such as 1.15:1 or 1.25:1 mean a worse transmission line. An acceptable VSWR depends on system requirements. Several companies make transmission line test sets, sometimes called network analyzers.

Instructions
    • 1
      Shut off the transmitter and disconnect the transmission line. Connect the output of the transmission line test set into the input jack of the directional coupler. Connect the through output jack of the directional coupler to the transmission line. Connect the return signal output jack of the directional coupler to the input jack of the transmission line test set.
    • 2
      Check your system application to ensure that sending a signal over the antenna system will not cause interference to any other systems. Remember that your antenna is still connected, and the test set can transmit signals outside of your allowed frequency. If you are unsure, have a qualified technician disconnect the transmission line from the antenna and install a dummy load in place of the antenna.
    • 3
      Turn on the transmission test set and send an output frequency or frequency range compatible with the signal you are sending over your transmission line. Wideband systems require the test set to "sweep" across the entire range of frequencies the system uses because VSWR characteristics change with frequency.
    • 4
      Read the results of the test from the meter. Some give an analog or needle display and others give a digital display. More elaborate models may give a screen display as the test set sweeps across the frequency band, and the results can be kept in memory or connected to a printer for a hard copy.
Tips & Warnings
  • To evaluate your transmission line, compare the test results to your system or equipment manufacturer's specifications. More complex systems require better VSWR performance.
  • Some transmission line test sets give results as "return loss." Note that 1.11:1 VSWR equals a return loss of about 26 dB. See jampro.com for a conversion table.
  • Many transmission line test sets come in a kit with a selection of test cords, dummy loads, adapters and a directional coupler.
  • Transmission line test set prices increase with complexity and some high-end models work for several applications. For economy, choose a test set that works specifically for your system.
  • If you test a transmission line with the antenna connected, and the results are bad, you could have a bad antenna. For best test results, install a dummy load at the end of the transmission line to exclude the antenna from the test.
  • Never climb a tower to install a dummy load unless you are a trained and qualified tower worker and are familiar with all safety procedures and regulations. Never allow an unqualified person to climb your tower. If you do, you could be liable for any damage, injury or death.
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