The Two Metre Cable is now measured at a lower frequency and the result obtained compared with the earlier result in paragraph 3.2 to demonstrate the decrease in insertion loss. In this measurement, RG58 will again give easier results than RG223, but it requires the same cable as used in paragraph 3.2 in order to compare the results.
INPUT POWER
The test equipment is connected as per Figure 2.2. The Signal Generator is set to give an output of +13 dBm ( or 1 Volt rms ) at a frequency of 1 MHz. The input power to the Two Metre Cable is obtained by first recording the input Voltage and Current and then linearising the results. The power is then calculated with Formula 3.1.
Formula 3.1 P = V x I Watts
OUTPUT POWER
The equipment is now reconfigured as per Figure 3.1. With the Signal Generator still set to give an output of +13dBm at a frequency of 1 MHz. The output power from the Coaxial Cable is obtained by first recording the output Voltage and Current. These results can now be used to calculate the output power from the Coaxial Cable using Formula 3.1
ATTENUATION
The attenuation of the coaxial cable at 1 MHz is now calculated using Formula 3.2
Power Ratio dB = 10 Log P1/P2
This is the insertion loss at 1 MHz for 2 metres of cable. When this result is compared with the insertion loss at 100 MHz for the same 2 metre cable measured in 3.2, it can be clearly seen that there is a decrease in the attenuation of the Two Metre Cable with a decrease in frequency. Thus proving that the attenuation of a coaxial cable is dependent on frequency. It should be noted that there was correction for the Voltage / Current Detector frequency response and a more accurate result can be obtained by normalising the frequency response.
5 > Page Number