Davis RF sells quality antenna W2DU Current& SPIRO Voltage type Baluns. Each is quality constructed with stainlesssteel eyebolts, 600 lb pull strength, in a weatherized package. We sell onlythe best! Additional technical information on Balunsis provided below the table.

BALUNS: What they are and when touse them.

There has been much written about Baluns. Ifyou want the real "nitty gritty" on all the technical aspects, a goodreference is Reflections, by Walt Maxwell, W2DU and is availablefrom one of our dealers, Radioware-Radio Bookstore (call 1-800457-7373).

For those of you who want a quickunderstanding, here it is. Coaxial Cable, as opposed to Balanced (ladder) Line,is an "unbalanced" feed line. Unless the feed line impedance isrelatively the same as the impedance of the antenna, some RF energy will returnback down the outside (shield) of the coax. This represents lost radiation andoften radiation in the form of RFI (RF Interference). To avoid this problem, aBalun is interjected at the antenna feed point to act as a choke, i.e. to chokeoff that portion of RF wanting to feed back down the shield of thecable.

Resonance, Impedance, and 1:1 vs4:1.
Resonance in an antenna occurs when the current and voltage are in phase. Thiscan be achieved if the length of the antenna is 1/2 wavelength. If the antennais resonant at a frequency, it is a resistive load. "Life isn'tperfect", so most of the time it is both resistive and reactive, thusexhibiting an impedance. Resonance in a general sense, allows the mostefficient radiation of the antenna. A resonant 1/2 wave dipole made of wirewill have an impedance of about 55-65 ohms. Use of a 50 ohm feedline will"match" the antenna's impedance. If the antenna is designeddifferently and its impedance, for example, is 200 ohms, then you would use a4:1 Balun (4 times the 50 ohm coax impedance). If you are resonant at afrequency, and don't work too far from it, no balun is needed. If you work thewhole band, a 1:1 usually helps "choke" RF from going back down thecoax shield. As an aside, if your antenna is 300 or 450 ohms impedance, you canfeed it with a 300 ohm or 450 ohm Balanced Ladder Line.. However, you will needa tuner at the transmitter to match the line to the 50 ohm transmitter oramplifier.

Voltage vs Current Baluns.
Voltage Baluns provide equalization of voltage in each leg of an antenna. ACurrent Balun equalizes the current flow. So which do you use? Based upon thematerials which are used for each type, the following is a simplistic rule: for4:1 - use Current Balun for high power (1000W+) or Voltage Balun for low power.1:1 - use Current Balun for either low or high power with low SWR. Generally,the Current Balun is the best choice if you meet the aforementioned criteria.Don't forget; no balun is needed if you design the antenna for one frequency,or at mid-band, and you find operation is OK at the band limits without highVSWR.

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