Inv. L antenna at 160m
One of the basic problems of short and low antennas for the 160m band is their low impedance at the power point, often only a few ohms. A simple and popular trick, how to overcome this wickedness is to deliberately extend the given antenna. This increases the real component of the input impedance at the power supply point, but an imaginary impedance component of an inductive nature also appears here. The solution is offered by inserting a serial capacity, e.g. of the rotary capacitor of a suitable value.
The total length will be 50.3 m, vertical part with a length of 12.3 m, the horizontal part is 38m and the impedance at the supply point is then 50+j88 ohms. In this case, there is no need for any long laboratory work with an impedance bridge or other devices, and by simply inserting a variable capacitance of 1000pF in series, we can get help from the mentioned +j88 ohms of the reactive component of the impedance.
Let's try to make the vertical part that high, as possible. Changes in impedance can be easily adjusted with a rotary capacitor in series with the antenna.
The ground system must be as good as possible, so don't be afraid to use everything, what do you have in your garden, including a chain from the dog…hi.
If you will use the antenna on higher bands, there is no need to worry much about the capacity in the series. The impedance of the capacitor will be very small at higher frequencies and the effect almost negligible. Heard on 160m.
Orig.pramen: NS8O, Greg Weinfurtner, Athens, USA.
