HAM Radio 101

What is an Antenna Capacity Hat?

Back in the day, folks used to say that you’re never fully dressed without a hat. In the Ham world, DX Engineering Hot Rodz® Adjustable Antenna Capacity Hats for select vertical mobile and base station antennas make more than a fashion statement.

DX Engineering capacity hats—a series of horizontal stainless steel rods attached to the top of the antenna—offer a proven solution for improving gain and efficiency of single-band mobile verticals, such as Hustler and screwdriver-type adjustable frequency antennas from manufacturers including Diamond and MFJ. Hot Rodz can even shorten the height of a screw driver antenna by replacing the six-foot whip with a 24-inch mast while maintaining or increasing the antenna’s efficiency.

When an antenna is shortened from its natural resonant length, the feedpoint becomes capacitive. To offset the additional capacitance, it is common to add inductance in the form of a loading coil to restore the resonance. However, the additional inductor increases the resistance, which increases the loss of the antenna.

Hot Rodz Capacity Hats add horizontal elements to the top of a vertical antenna, which reduces inductor resistance and counters the effects of the shortened vertical antenna. Extensive testing has shown that the improved efficiency and reduced loss resulting from use of a Hot Rodz Capacity Hat can significantly increase the RF power radiating from your antenna.

For specs, efficiency charts, installation instructions, and technical details, check out the DX Engineering Hot Rodz Adjustable Capacity Hat Manual.


Leave a Reply