Topband: 160 Meter Three Element Short Vertical Receiving Array

[donovanf at starpower.net]

Reply to: alanbh at cablespeed.com 


160 Meter Three Element Short Vertical Receiving Array. by WA3EKL 

I recently designed and built a three element triangular short vertical array for 160. At the encouragement of W3LPL, Frank, I wanted to share my experiences with the reflector. 

I live on the outskirts of noisy suburbia. Weakest band is 160 receive. Have tried numerous 160 receive antennas. Five element BOG (beverage on the ground) has the been the best so far until this system. The vertical array has more output, better front to back and appear to have considerably more directivity than the bogs. 
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Two elements are always active in an end fire cardioid pattern and the third element is electrically made to disappear via a shorted length of ¼ wavelength of coax switched to its feed line. This is done with four double pole double throw relays. 

The verticals are spaced 67 feet apart or 1/8 wavelength on 160, fed 135 degrees out of phase creating the cardioid pattern with 4.2 db gain over a single vertical and about 24 db front to back ratio. The nose of the pattern can be switch every 60 degrees around the compass with the four relays. 


The relay switching box uses a 180 degree reverse phase transformer and a 45 degree phasing line to create the 135 degrees of delay, plus a zero degree hybrid combiner and step up transformer all wound around three tiny Amidon BN-73-202 binocular cores per ON4UN’s design in his book Low Band DXing. 

There is much information everywhere about24 foot short receiving verticals for 160 that use top hat wires. After a week of searching I could find nothing on short verticals that do not use top hat wires except for two sources. W3LPL’s Antenna University and ON4UN’s LowBand DXing Book. Frank, W3LPL stated short low impedance verticals without top hat wires needed to be 35 feet tall. ON4UN used 36 foot verticals. 

My verticals are 35 foot of Aluminum. 18 feet of heavy wall 1 1/8 inch, 6 feet of 1 inch heavy wall with 5 feet sticking out, then 12 feet of ¾ inch all from used antenna parts. They are attached to pressure treated six foot 4x4 posts cemented 18 inches into the ground. The lower four feet is wrapped with three wraps of Scotch 33 tape. A 4 foot piece of 1 ¼ inch PVC was split in half and the two sections were then put back around the bottom four feet of the pipe. The PVC is then clamped and screw to the posts with 1 ½ inch steel conduct pipe hangers (Lowes model 67840.) If you use pressure treaded wood be sure and use stainless steel hardware because pressure treated wood increases the rusting of galvanized steel very quickly! I have stainless steal flat washers between the wood and the galvanized fitting. You can’t get the hanger in SS. 

Since I didn’t have room for top hat wires I don’t have room for long ground radials either. Ham Radio Magazine many years ago ran an article about someone who did some experimenting on ground screens for 160, 80 and 40. His conclusions were this. The most efficient ground screen for 160 was a piece of 1 inch poultry mesh (aka chicken wire) 25 feet long and 5 feet wide crossed with a piece 40 feet long and 2 feet wide. The next most efficient was to delete the 40 foot piece. 


I started with two 3 foot wide 25 foot long pieces placed side by side under each antenna. At the center where the antenna sits I sowed through the mesh two pieces of number 12 bare copper wire in the form of and “X” so that each piece went through both sections of mesh. Then I soldered the copper wire to the galvanized mesh. Yes you can solder to the galvanized mesh if you do it correctly. 

Using a RigExpert AA-30 antenna analyzer I needed about 110 micro henrys to bring each antenna to resonance at 1830. 


Antenna A is sitting over pure lawn grass on a fence post that divides the front yard from the back yard. The entire ground screen is over lawn grass and the grass growing through it. Antenna B sits at the edge of my lawn and my woods. ¼ of the ground screen sits on lawn grass and the remaining ¾ sits on forest floor. Antenna C sits in the woods on pure forest floor. 
My first attempt to tune the antenna number one was to wind 11 turns of single strand of cat 5 cable on a Amidon FT-114-43 coil form. I successfully tuned the antenna into the 160 band but not at the freq I wanted. Removing or adding a turn moved the resonate point 33 KHz and spreading the turns could not get me close enough. At a resonate point of 1852 with no”X” or reactance the resistive component remaining was 330 to 350 OHMS. Not good. Checking the Amidon site, 43 ferrite material is rated good for 20 Mhz to 50 MHz. DON’T USE 43 FERRITE MATERIAL. In ON4UN’s book he used Powered Iron T-130-2 type cores. Type 2 is rated 2 MHz to 30 MHz. Type 1 materal is rated 0.5 MHz to 5 MHz. I ordered three T-130-1 and three T-130-2 plus three each of T-1061- and T106-2. The T-106 coil forms are slightly smaller with a higher AL value thus requiring less turns to accomplish the same inductance and have the same frequency rating. I settled on using the T-130-1 material which took 55 turns of single strand cat5 cable that filled up about 85 % of the coil form. Using a T-106-1 takes 35 turns but fills the entire coil form not allowing for any tuning room. 


Per the RigExpert Analyzer when Antenna A was tuned to resonance at 1830, zero reactance, the remaining resistance was 26 Ohms. Remember it was on pure grass. Antenna B on ¼ grass when resonate at 1830 showed 44 Ohms of resistance. Antenna C on pure forest floor at resonance at 1830 showed 52 Ohms!. Adding the correct amount of resistance in series with the coil brought each antenna up to near 75 ohms. Then I decided to added the 40 foot by 2 foot cross piece of chicken wire to see what would happen starting with antenna C on the pure forest floor. The resonate frequency moved down to 1820 which meant I needed less inductance and the resistance at 1830 resonance dropped by 6 ohms. Antenna number B was next. Its resonate frequency dropped to 1810 and when resonated back to 1830 its resistance dropped 5 ohms. In both cases I just had spread a few winding on the coil to bring the antenna back to 1830. Also tuning of each coil was much less critical this time. Antenna A dropped even less in frequency. My final numbers came out to; 
Antenna A 71 ohms at 1830 with a series resistor of 47 ohms. 
Antenna B 74 ohms at 1830 with a series resistor of 27 ohms. 
Antenna C 72 ohms at 1830 with a series resistor of 22 ohms. 


The coax from the control box to each antenna is buried and the coax back to the shack is buried. There is enough output from the array that I do not need an external preamp. The preamp in the K3 is enough when I need it. 


I hope this information will help someone who is deciding to build a 160 receiving array this summer. 
This is my first post to the reflector. I know its long winded but I wanted to give you all as much information as possible. 


73 
Alan 
WA3EKL