One of the basic problems with short and low antennas for the 160m band is their low impedance at the feed point, often only a few ohms. A simple and popular trick to overcome this disadvantage is to deliberately extend the given antenna.
This will increase the real component of the input impedance at the power supply point, but at the same time an imaginary component of the inductive impedance will also appear here. The solution is to insert a series capacitance, for example a suitably chosen rotary capacitor.
Practical realization of the antenna on 160m
The total length will be 50.3 m, the vertical part 12.3 m, the horizontal part 38 m and the impedance at the supply point will be 50 + j88 ohms. In this case, there is no need for long laboratory work with an impedance bridge or other devices - by simply inserting a variable capacitance of 1000 pF in series, we get rid of the mentioned +j88 ohms of the reactive component of the impedance.
Let's try to make the vertical part as high as possible. Changes in impedance can be easily adjusted with a rotary capacitor in series with the antenna.
The ground system has to be the best it can be, so don't be afraid to use whatever you have in the garden, including the dog chain…hi.
If you will use the antenna on higher bands, you don't need to worry too much about the capacity in the series. The impedance of the capacitor will be very small at higher frequencies and its effect almost negligible. They will hear on 160 m.
Original source: NS8O, Greg Weinfurtner, Athens, USA.