When searching for a suitable antenna for the HF bands, I came across many interesting designs that had only one flaw - they could not fit into the space I had available. Short antennas, electrically extended, seemed 'sharp', the bandwidth was only a few kHz. The Inverted L has the advantage of simple construction, small footprint, and a wide bandwidthThe antenna has so far ended only as a theoretical design waiting to be tested, as I chose a different antenna for home. QTH I chose a different antenna.
Advantages of the Inverted L antenna
The problem with short vertical antennas is the low impedance at the feed point, which significantly reduces the efficiency of vertical antennas compared to the comparable ground plane resistance. You can also find this antenna in the ARRL Handbook or Rothammel Antennenbuch. The Inverted L benefits from extending the radiator, increasing the impedance (thus increasing the efficiency of the antenna with the same ground plane) and compensating for the reactive component of the impedance by inserting a capacity into the feed point of the antenna.
Since this is an experiment, part of the description is a program file MMANA, in which the antenna was designed.
Antenna construction
Since the Inverted L is a vertical antenna, we will need a ground plane. We will create it by burying (or attaching to the ground) quarter-wave radials - 20.4m. Their number or shape is not critical, a minimum of three radials are required, which can be bent if necessary. We will need about 25.5m of wire for the radiator, which we will attach to the space according to the picture. Trees or buildings can be used as support points.
Uncompensated antenna exhibits a significant reactive component of impedance. Compensation is achieved by adding a series capacitor between the end of the antenna and the feeder. Caution - the capacitor must be able to handle the required power! For portable antenna use, a tuning capacitor is suitable, in home conditions it is better to replace the capacitor with a quality fixed capacitor (ceramic, mica) after adjustment. The capacity according to MMANA is about 165 pF.
Antenna tuning
The antenna is tuned to a minimum PSV capacitor. If it is not possible to achieve a 1:1 PSV, it is necessary to adjust the length of the radiator. A properly tuned antenna should have a bandwidth for a 2:1 PSV of almost 150kHz, gain relative to an isotropic radiator of 1.3 dBi (-1 dBd), which is quite acceptable due to the dimensions of the antenna.
MMANA for simulating antenna properties
MMANA is a handy helper that will help you navigate the properties of the antenna even before its construction. For example, by changing the dimensions of the antenna, the ground plane, the matching circuit, you will create a comprehensive picture of the antenna's behavior. And if the antenna passes these tests, it is worth trying it out. The MMANA file for the inverted L antenna on 80m is .: HERE :.The antenna caught my attention, so I look forward to testing it from some temporary location.