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WE-030B Antenna Analyzer Applications


1) Basic Antenna System SWR Measurements

SWR and Return Loss of an antenna system can be directly measured.
2) Antenna Trap Resonant Frequency Measurements

See  WE-030A Video


3) Vertical  λ/4 Monopole Antenna Feed Impedance Measurement

The feed point impedance of  λ/4 monopoles ( full size or loaded ) and derivative antenna, eg directional arrays  and trapped verticals etc can easily be measured at resonance with this product. An effective method is to install a choke balun at the end of the interconnecting 50 ohm coaxial cable near the feed point , then move the measurement reference plane to the end of the cable on the antenna analyzer, and then measure the impedance on the analyzer.

Why is this impedance useful to know? At resonance this impedance will be resistive. For a full size ideal λ/4 wavelength antenna over an ideal ground plane, it's value will be 37.5 ohm. In practice it will measure higher than this mainly due to non-ideal ground. Knowing the difference between the practical measured value and the ideal value enables an estimate of the antenna efficiency to be made.

Why bother with the choke balun? The choke balun substantially isolates the test set-up from the antenna, and prevents the test set-up from influencing the measurement results. Why are these measurement results effected? The effect is due to the interconnecting coaxial cable and the body of the operator forming part of the antenna system by virtue of the feed point connection.

4) Choke Balun Impedance Measurement

The common mode impedance of the choke balun can easily be measured by connecting the coaxial outer braid ends of the balun across the port on the analyzer. An Impedance of > 1000  should ensure adequate isolation for typical antenna's.

The differential mode impedance can also be measured by terminating the output with the correct load impedance, and directly measuring the input impedance.

5) Antenna Loading Coil Inductance And Derived Q Measurement

Typical loading coils for HF mobile whip antennas can have a reactance at their operating frequency of several thousand ohms. As these large value impedances are outside the measurement range of the WE-030B the inductance should be measured at a much lower frequency than the operating frequency.

Note the Q of these coils can not be directly measured, but the series resistive loss resistance at the operating frequency can be directly measured by connecting a very high Q series capacitor of reactance equal in magnitude to the inductors reactance to form a series resonant circuit at the measurement frequency. The Q of the capacitor must be very much larger than that of the inductor, so the resulting series resistance is predominately from the inductor.

The Q of the loading coil can be calculated from the ratio of the inductive reactance to series resistance at the operating frequency.

6) Direct Measurement Of Impedance Matching Elements

The element impedances can be measured directly.

7) Adjustment of  λ/4 Tuning Stubs

Connect the stub to the analyzer, and adjust its length for minimum impedance and zero reflection phase angle.

8) Measurement of Coaxial Cable Loss

This is simply measured by first connecting one end of the cable to the analyzer, leaving the other end open. The return loss ( in dB)  is then measured at the desired frequency. The cable loss is the return loss number measured divided by two.