MIL-DTL-49295C
4.8.3 Reference dipole antenna. The reference dipole antenna for gain measurements shall be a vertically
polarized balanced dipole. Length of the dipole shall be continuously adjustable. At each test frequency, length shall
be adjusted to half-wave length resonance, considering end effects (usually 95 percent to 97 percent of one half
wave length). When so adjusted, free space VSWR shall be less than 2.0 to 1. The coupling balun shall have a 1 to
1 impedance ratio. Balun coupling loss shall be less than 1 dB. The transmission line shall be the same line or an
identical line to that of the antenna under test. Free space VSWR of the antenna and coupling loss of the balun shall
be measured over the frequency range of the antenna under test. Maximum VSWR and maximum coupling loss
shall be recorded in the space provided for on the test data sheet for gain measurements. A typical antenna for this
purpose is shown in figure 1.
NOTES:
1. Indiana General part # F624-19, 02, ferramic toroid or equal with 10 turns #18 enameled wire, trifilar
winding.
2. Whip sections must extend anywhere from 25 feet to 8.5 feet to adjust to frequency of measurement.
3. Value of capacitor to be selected so as VSWR of the balun is 1:1 across the frequency range of the balun.
FIGURE 1. Reference dipole antenna.
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