Inverted-L Experiences
March 2021

  My first inverted-L was built in the backyard when I lived in Stone Mountain GA. The vertical section was ~50 feet. The length of horizontal section has been long forgotten. The distance between the trees supporting the antenna were over 100 feet apart. The wire was intentionally cut long and its length was adjusted using wire thimbles and clamps to get the best SWR. The antenna was fed with coax and no other attempts were made to further tune the antenna. A make-shift ground round took the place of radials.  
  The first antenna raised in Stone Mountain was a 160M full-wave loop hung in the front yard of the 3+ acre property. With various balanced tuners the antenna worked FB from 160M all the way up to 2M. Comparing the antennas revealed no noticeable difference between the loop and the inverted-L. The loop stayed and the inverted-L went away to be replaced with other experimental antennas. With loop 30 countries and 47 states were worked over several years.  
  After retiring to the current QTH a new antenna farm was needed. One of the first temporary antennas was an inverted-L for 160M with three radials. Using a thimble and wire clamps to tune for the best SWR was not completely successful. The rig managed to tolerate the SWR and had trial runs in the December 2019 ARRL 160M and Stew Perry tests. The results were acceptable.  
  After repeated failed attempts to tune the antenna by length it was time for research. There are several ways to provide a good match using L/C components. The simplest uses a variable capacitor in series between the coax' center conductor and the antenna wire. That was the chosen path to follow. Protecting the variable from mother nature's effects was the next consideration.  
  While at a big box home center I came across some inexpensive plastic mailboxes. Mother nature would be kept at bay with a mailbox and a 3 foot steel fence post. The variable was mounted on a piece of scrap wood with leads made for the external connections. The leads were fed through holes drilled in the plastic and the board was placed in the mailbox. A couple of screws through the bottom of the mailbox hold the board in place. A 1:1 balun was used at the feed point. One of the leads was attached to the balun and the other connected to the antenna wire. A number of radials were attached to the other side of the balun. The balun hangs from a cup hook screwed through the mailbox into the board.  
 
                     
 
  An antenna analyzer was used to adjust the variable capacitor to get the lowest reactance. The SWR seemed reasonable although the point closest to resonance was ~1925 Khz. A non-scientific comparison of the results from the 2019/2020 December Stew Perry and ARRL 160M tests suggests the changes were most beneficial. In the 2020 tests 41 and 43 states respectfully were worked. In 16 months of using the inverted-L 48 states (missing AK & WY) have been worked along with 39 DXCC entities. The best DX to the east has been the Ukraine (~4580 miles) while to the west is Hawaii (~4450 miles). Not bad for 100 watts and a hunk of wire.  
  Not everything was perfect however. At the low end of 160M the rig reported a 3:1 SWR. The resonant frequency of the antenna needed to be lowered. Looking at the variable capacitor revealed it was fully meshed with a value of ~465 pF. A 250 pF silver mica capacitor was put in parallel with the variable. The antenna analyzer was used to set the reactance to its lowest point. After the modification the rig shows an SWR of ~1.7:1 or lower between 1800 and 1925 kHz.  
  The antenna's performance is a combination of factors including propagation and the operator at the other end of the QSO. A major factor may be the radials. The antenna runs down one side the 250 foot gravel driveway. On the other side of the driveway is a 500 foot property line. Because the antenna's feed point is at the end of the driveway only a 90° of radials can be laid. Actually plus one which was laid over the buried cables.  
  At present on seven radials have been laid in the quadrant. There is a small stream behind the house which may help ground conductivity. In any case once the weather warms up more radials will be laid. Two of the radials will terminate at ground rounds driven into the stream bed. The radials are held in place using staples made of aluminum electric fence wire.  
  It's a combination of these factors which help make my inverted-L a winner.  
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