1:1 Balun - 50 ohms balanced to 50 ohms unbalanced (coaxial)
    For 1/2 wave dipole or yagi beam
    For tranceivers, linear amplifiers, LC tuning networks
    1 MHz to 50 MHz
    5 KW to 10 KW
    Dimension 5.5" x 3.8" x 2.3" (*6.8" including flanges)
Model BAL-50 pdf
The BAL-50 W2FMI-1:1 balun is generally designed to match 50-ohm coaxial cable to the balanced loads of center-fed half-wave diapoles or Yagi beam antennas. Feeding the balanced diapole with coaxial cable will upset the balance as one side of the antenna is connected to the shield while the other side is connected to the inner conductor. This results in reduction in gain, increase in VSWR and RFI interferences. Use W2FMI 1:1 balun to reduce these.
The W2FMI-1:1 is also used to match the unbalanced outputs of tranceivers and linear amplifiers to the input of a balanced L-C tuning network.
When to use and when not to use a 1:1 Balun:
Since feeding a center-fed half-wave diapole with coaxial cable creates a very small imbalance at the feedpoint (because the diameter of the cable is much smaller than the wavelength), a 1:1 balun is generally not needed in the HF and VHF bands. Experiments have found it to be needed only when the coaxial cable does not come away at right angles from the diapole (for the plane of an inverted V). A 45 degree angle created a considerable imbalance.
With Yagi beam antennas it is a different matter. Since hairpin matching networks are usually employed, the effective spacing at the feedpoint is greatly increased and a 1:1 balun is required. Its biggest effect is the retaining of the antenna's beam pattern by preventing radiation from the feedline.
It must be pointed up that a 1:1 balun should never be used on the second harmonic of a half-wave center-fed dipole (like an 80 meter dipole being used on 40 meters). The impedance can be as great as 10,000 ohms creating very high boltages which can bring about voltages breakdown and/or excessive heating.

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