Surfing on the net I was reading an article about extreme small HF antennas. I found it a strange design, but reading the article made me understand the design. In fact it's very simple, we connect a capacitor, in the form of a copper or aluminum tube, in series with an inductor. That makes a resonating circuit on a fixed frequency.

The formulas below explain how we can calculate the antenna called the Microvert. Designed by DL7PE

The formulas below explain how we can calculate the antenna called the Microvert. Designed by DL7PE

The length of the tube can be calculated using the formula below:

The capacitance of the tube can be calculated with:

To calculate the inductor to make it resonant is calculated using the formula below:

The coax inner wire is connected with the inductor. The outer conductor of the coax is used as a counterpoise. These has a certain length which can be calculated.

After this length we need a RF-choke to block the return current. The RF-choke can be made of the coax about 8 turns with a diameter from about 10cm

Original Microvert article (PDF) (English)