Recently I have revised the rod antenna for my handheld QRP SBB transceiver. The main objective was to simplify the matching circuit. As I’ve pointed out before in the antenna article, one of the major problems with shortened antennas is the low feed point impedance. The first version of the antenna matcher used a capacitor and a coil to form part of a PI-filter. This new circuit uses an autotransformer made of a linear coil.
The tap is at about 1/4th of the total windings which transforms the feed point impedance of about 10 ohms to the coxial cable with 50 ohms. A 5 meter wire acting as the second part of the dipole should be used to increase performance of the rod antenna. All dimension concerning antenna length have remained unaltered, please see respective article!
use a Smith chart.
Cap to ground and series inductor, if you are stepping the impedance down from 50R.
Tuning cap will help find the value. Then replace it with fixed cap for 100-500V.
If you add ground radial wires (hanging 20cm above ground), there will be impedance change. But the whole antenna will work better.