We often get the question – Do I need a balun or an unun? The proper question is – do I need a feed line choke or an impedance transformer whose output is configured as balanced (balun) or as unbalanced (unun)?
A feed line choke is a 1:1 impedance transformer with equal input and output impedance (usually 50 or 75 ohms in/out). Impedance transformers in the Palomar Engineers’ product line have input/output ratios either less than 1:1 (like 50 ohm input to 25 ohm output) or greater than 1:1 (like 50 ohm input to 200 ohm output). Feed line chokes and impedance transformers can be configured as unbalanced or balanced output each having identical ferrite transformers. Feed line chokes are configured in CUBE™ (Common Unun Balun Enclosure) box enclosures or in “sleeves” with clip on beads or snap on beads, multiple ring toroids (Super Chokers™), or encased in TUBES. Impedance transformers and feedline chokes can be configured with either balanced output(balun) or unbalanced output( unun).
A few definitions in picture form:
Here are examples of UNUN output configuration differences:
Sleeve Unun Examples (click on image for more info)
Sleeve feed line choke ununs have a coax input and coax output as shown below:
|Feed line chokes configured as ununs with coax input and output|
Note: If the sleeve feed line choke had an output of two wires instead of a coax connector it would be called a sleeve balun (balanced output) and could be used with dipoles, beams, etc with two balanced outputs.
An impedance transformer (all ratios) can be configured as a voltage transformer (equal voltages on balanced outputs) or as a current transformer (equal currents on balanced outputs). Feed line chokes (1:1 impedance transformers) are almost always configured as current transformers and multi-ratio (<1:1 or >1:1) impedance transformers can be voltage or current transformers depending on the application. The ferrite transformers use slip on beads, snap on beads, ring toroids or binocular cores depending on power requirements, frequency range and impedance ratio required.