W2AU Series Baluns & Isolators

long the standard of the industry the W2AU baluns are built to last!

The W2AU is the preferred Balun of Amateurs worldwide. W2AU’s operate at a low VSWR from 1.8 to 40 mHz, and handle powers up to 2 KW PEP (at SWRs of less than 3:1).

W2AU Baluns are transformer designs with ferrite cores to provide 95% minimum coupling efficiency. Each has a built-in lightning arrestor, hang up hook, and 600 lbs of pull-apart strength in a weatherized, rugged package using only stainless steel hardware and quality materials.

Two models are available. The 1:1 matches 50(75) ohms unbalanced coax to 50(75) balanced dipoles. The 4:1 matches 50(75) ohm unbalanced coax to 200(300) ohm folded dipoles.

For matching yagi or quad elements select the Beam models of the famous W2AU or W2DU Baluns. These models are designed to be mounted horizontally to a beam’s boom. Pigtail wires are provided in lieu of the hooks on the wire models to connect these Baluns to the driven element. Specs for beam models are the same as their respective wire models with the exception that the W2AU and W2DU HF beam models only operate from 40 to 10 meters.

Likewise our IN-LINE ISOLATORS have an SO-239 UHF type connector on both the input and output side. In-Line baluns provide similar performance to their respective wire balun counterparts. Applications for In-line baluns include line isolation anywhere along the coax transmission system and use on Quad and Yagi antennas. The W2DU’s RF choke design can be used anywhere along your coaxial transmission path to help eliminate RF feedback and TVI.

While the RF currents flowing along the coax shield are “choked” out by the balun/isolator, the internal 50 ohm signal is completely unaffected. Some users have noted a reduction in interference with the use of line isolator between their transmitters (transceivers) and linear amplifiers. Another use is placing one at the vertical, beam, or quad antenna to augment the antenna’s matching system to coax.

= All W2AU series baluns are VOLTAGE type designs =

These fine Antenna products are now available only

through Amateur Radio Dealers and Integrators

Model # Description MSRP(US)
W2AU 1:1 50 ohm-50 ohm or 75 ohm-75 ohm (Transformer Type 1.8 – 40 MHz) $35.00
W2AU 4:1 200 ohm-50 ohm or 300 ohm-75 ohm (Transformer Type 1.8 – 40MHz) $35.00
W2AU 1:1-B 1:1 Beamed Version (Transformer Type) $36.00
W2AU 4:1-B 4:1 Beamed Version (Transformer Type) $36.00
W2AU 4:1 LL Ladder Line/Coax Transition 4:1 Balun $37.00
W2AU INLINE W2AU-1:1 Isolator with Double SO-239 Connectors $37.00


Since many Hams are the inventive types, it should noted that they also tend to not read the instructions and succeed in achieving their goals.

In any event, the matchbox is a tuner and all it does is make the transmitter believe it has an antenna with a lower SWR than it really has. This way it will introduce more power to the antenna than it can typically radiate.

A random length antenna, one not tuned to any one frequency is a compromise antenna. Anywhere it is not resonant it will produce significant SWR’s above 3:1.

With 200 watts of continuous key down CW it would heat up the core of the W2AU balun, at the feed point,and damage it, but that is the extreme example. Many Hams understand this and do it anyway with care.

Also, note that new solid state equipment further limits your operating options never contemplated over 50 years ago when these instructions were made. The equipment manufacturer dictates the parameters of your operating ability.

It is suggested that if using ladderline, no balun, because a balun at the feedpoint, would interfere with the radiation that the offset antenna needs from the ladderline.

Instead use a ” W2AU 4:1 Ladder Line Balun ” at the end of the ladder line transitioning the ladder line to a coax entry into your shack. A 4:1 extends resonances available. Some hams use a 1:1.

These are some ideas in using an offset antenna.

Remember your ABC’s – ALWAYS BE CAREFUL