1. Experiment 17-FP calibration

This Experiment measures a dipole which is one-half wavelength at 150 MHz. This is intended as a reference antenna able that is to produce a known ERP by efficiently converting all of the source power to radiated energy in a known manner. The Experiment calibrates a Field Probe at a single frequency.

It is connected via a test fixture which is a bazooka balun, made from three tubes in a coaxial structure. The central part of this balun is conventional, approximately 63 ohm (TEM) transmission line made from concentric inner two tubes. A larger diameter outer tube is placed around these to create a high impedance to common-mode current. At 150 MHz, all together the three tubes provide conversion from 50 ohm the singled ended connection of the VNA to balanced 74 ohms, the approximate impedance of a half-wave dipole. Unlike other fixtures in these experiments, this one is designed for a single frequency or narrow band use.

Figure 1 shows the test environment for calibration using a well matched 1m reference .

This reference antenna is connected to Port 1 of the VNA while Port 2 is connected to an N6GN Field Probe¹. The antenna on the probe has also had its length adjusted to become a half-wave at 150 MHz.

A comparison of measured strength at 2m and 3m spacings is shown in Figure 2

Measurement of loss from matched horizontally polarized reference antenna to FP output is given in Figure 3