“Cat’s whisker” 5-band Dipole Antenna

The term “Cat’s whisker” dipole is a colloquial name for a fan dipole or parallel multiband dipole. It is an incredibly efficient, low-cost way to operate on multiple HF bands using a single coaxial feedline, avoiding the losses and bandwidth restrictions of traps or the need for a remote antenna tuner.

How It Works

A “cat’s whisker” consists of multiple half-wave dipoles cut for different bands, all joined in parallel at a single center insulator or 1:1 balun.

When you transmit, no physical switching is required. The RF energy automatically seeks the path of least resistance. The dipole element that is resonant at your transmission frequency will present a very low impedance (typically around 50–70 ohms), while the non-resonant elements will present a very high impedance. The RF naturally flows almost entirely into the resonant element.

A Typical 5-Band Configuration

If you want to cover five bands—such as 80m, 40m, 20m, 15m, and 10m—you only need four sets of wires. This is because a dipole naturally resonates on its odd harmonics. The 40m element will act as a 3/2-wave dipole on 15m, giving you that fifth band for free.

Here are the approximate starting lengths for each leg (arm) of the dipole:

• 80m element: ~19.3 meters (63.3 ft)
• 40m / 15m element: ~10.1 meters (33.1 ft)
• 20m element: ~5.0 meters (16.4 ft)
• 10m element: ~2.5 meters (8.2 ft)

Construction and Tuning

Building the antenna is straightforward, but tuning requires patience due to how the elements interact with one another.

1. Separation is Key: The wires must be physically separated to minimize capacitive coupling. If installed horizontally or as an inverted-V, you spread the ends out wide like a cat’s whiskers. If the wires must run parallel, use PVC or lightweight fiberglass spacers to keep them at least 4 to 6 inches apart.
2. Tune Longest to Shortest: Always cut your wires a few inches longer to leave room for tuning. Start by transmitting on the lowest frequency band (e.g., 80m) and pruning the longest element for the lowest SWR.
3. The Ripple Effect: Once the 80m element is tuned, move to the 40m element. Here is the catch: trimming a shorter element will slightly shift the tuning of the longer ones. You will usually need to iterate through the bands two or three times until the SWR is acceptable across the board.
4. The Feedpoint: While you can feed a cat’s whisker directly with coax, using a 1:1 current balun at the feedpoint is highly recommended. It prevents common-mode currents from traveling back down the coax shield, keeping RF out of your shack.