75 / 80M FOUR SQUARE ARRAY

In the left photo is one of four Force12 EF-180BV shortened 80m verticals. These linear loaded verticals are approximately 34 feet high and have 64 ground radials under each. The array is fed using a COMTEK ACB-80 hybrid coupler (See right photo) .

This array was originally installed in the fall of 2000 with four elevated radials per vertical then upgraded in subsequent years first to eight and then to sixteen radials to improve performance. In the summer of 2003 the elevated radial system was replaced with (64) 1/4 wavelength ground mounted radials under each vertical. The 64 ground radials reduced ground loses in the near field better then the 16 elevated radials. The array produces a minimum dump power 50% less then that from the old elevated radial system (~2.5% Vs ~5%) and is also easier to tune.

While this array was originally setup for the phone DX window (3790 - 3800 KHz), In the summer of 2006, I modified it to also operate down at 3500 KHz as well. In the middle photo you can see a close up view of one of the vertical feeds. The large enclosure at the top houses a loading coil and relay for resonating the vertical at ~3500 KHz. Below this enclosure is the verticals hairpin feed, balun, and phasing line switching box. The switching box and phasing line entering the box from the bottom is used for proper phasing in the phone DX window. When operating down at ~3500 KHz the short phasing line to the right of the switch box is added to the existing configuration. Control lines for both the loading coil and phasing line switch boxes for each vertical run back to the center of the array (upper enclosure in right photo) and then to the shack where an additional switch was added to the COMTEK controller box.

On air testing has indicated that this array using shortened verticals hears as well as those using full size elements and is only slightly down on transmit. Test data for both SSB and CW bands are listed below.

 

SSB BAND

 

 

 

 

 

 

CW BAND

 

 

 

 

 

 

Northeast Vertical
Northeast Vertical Feed
 
Min Dump
10% Dump (low)
10% Dump (high)
Useable BW
NE
1.8% (3.798 MHz)
< 3.750 MHz
3.865 MHz
115 KHz
SE
1.7% (3.798 MHz)
< 3.750 MHz
3.878 MHz
128 KHz
SW
1.8% (3.798 MHz)
< 3.750 MHz
3.862 MHz
112 KHz
NW
1.8% (3.798 MHz)
< 3.750 MHz
3.875 MHz
125 KHz
 
Min Dump
10% Dump (low)
10% Dump (high)
Useable BW
NE
2.0% (3.505 MHz)
< 3.500 MHz
3.551 MHz
51 KHz
SE
2.6% (3.505 MHz)
< 3.500 MHz
3.547 MHz
47 KHz
SW
1.8% (3.505 MHz)
< 3.500 MHz
3.552 MHz
52 KHz
NW
2.4% (3.505 MHz)
< 3.500 MHz
3.548 MHz
48 KHz
Modified Comtek Hybrid Coupler