An adaptive high power vector network analyzer for the tuning of NDB transmitter antennas

Reliable impedance measurements of installed HF air navigation antennas are possible with an automatically adjusted high power analyzer using levels above 30 dBm to overcome external interference signals coupled from the environment. Even a bad mismatch of an unknown device cannot cause unpredictable results or test equipment failures if this straightforward method is applied. The proposed adaptive network analyzer covers frequencies between 100 kHz-50 MHz and regulates the test port power down to 10 dBm according to the return loss and, thus, reduces the risk of damage and, at the same time, improves resolution at the other end of the return loss scale above 25 dB. The rejection of the misleading effects of unwanted signals can be further improved by the built-in modulation.