I first started thinking about this antenna in the mid-1980s while at my Bear, Delaware, location. I had a 100-foot vertical
for 160 meters there, and had planned to add sloping reflectors. There were some articles in QST and the ARRL Antenna
Compendiums on sloping wire arrays that kept this idea alive for me. But a move to a new QTH north of Wilmington in
1991 -- with no room for such an array -- put the plans on the back burner.
When my wife Jeanie's (AB1P) job change gave us the opportunity to move to a rural central Delaware location in December
1997, we started planning for a multi-element 160-meter transmit array again.
The initial plan was to use a modified K3LR array, as described in ON4UN's Low Band Antennas book. Mine would be limited
to 100 feet. The sloping T shaped parasitics would be spaced out 66 feet from the series-fed driven element in four directions.
Relays switch these as floating, director or reflector to give us three elements aimed NE, SE, SW or NW.
Because the central tower was only 100 feet instead of 128 that Tim, K3LR, used, my parasitic elements had a shorter
vertical section -- 65 feet vs. 75. I used small loading coils to resonate the directors around 1930 khz, as well as small
coils to resonate the reflectors around 1740 kHz. I was getting some f/b and gain, but Tim had advised that it was really
necessary to use a remote signal source a mile or so away and adjust the reflector coil for best f/b.
Other projects -- new towers and phased Beverages -- kept me away from this project for the last couple of years, but
I made it a priority to have this going before the 2005 CQ WW 160 meter contest.
I also decided to add another tower to give me an additional director toward Europe. This models as giving an additional
1 db gain in that direction -- the "boom" length toward Europe is now 229 feet. The new tower, 90 feet, uses a small coil
to resonate at 1930 kHz. This also allows me to raise the catenary holding the sloping wire first director, shortening the
top hat. I may also add another director in between the existing directors, for a total of 5 elements. This would increase
the f/b a bit.
Another new tower to the SE also will allow me to add another director in that direction, and perhaps another one to
the SW as well, once I move a 40-meter yagi off to give us enough clearance on the Rohn 45.
I finished the new Eu director tower a week before the 160m contest. When Jeanie was home for a snow day the Monday before
the 160-meter contest, she was kind enough to take the mobile rig out as a remote signal source so I could tune the reflector
coils for best f/b. The temperature was in the mid-teens Fahrenheit that day, and I was laying on the fresh snow making the
adjustments. There was a big difference in f/b from the plug-and-play settings I had been using. The reflectors ended up resonant
around 1780 kHz, as measured on my MFJ269B analyzer.
I was now seeing 5-6 db gain over the single vertical, and 20-25 db f/b.
Later in the week I restored the SE wire parasitic that had been removed while constructing the new tower in that direction
last fall, and added an element to the NW to complete the four directions. These two were simply tuned using the MFJ analyzer
to make the reflector resonant at 1780 kHz.
Results in the 160 meter contest were impressive. The TX array was actually better for receiving for much of the weekend
than the phased Beverages, particularly toward Europe.
I think there is still room for improvement. The new towers will allow me to use more vertical and less top hat on the
wire parasitic elements by raising the end height of the rope catenaries. I plan to borrow some ideas from John, W1FV, who
designed a 3-element parasitic array at KC1XX (details at www.kc1xx.com
) and who offered helpful advice in tuning up my array. I particularly like the way he brought all the element tuning to
a single box using half-wave feedlines, and I plan to implement that here to allow for better fine-tuning of the gain and
f/b or my array. That would also allow me to shift my driven element easily to one of the parasitics to allow for 6 or 7 elements
This array uses more than 600 radials -- 120 radiating from the driven element and from each original parasitc element.
At a midpoint between elements they are soldered to a buss line. Radials are 1/4 wave long unless they reach those buss lines
at a shorter distance. Wire was what I could scrounge up cheaply at the local scrap yards -- mostly No. 12 stranded THHN house
wire. Some is also No. 19 enameled.
Relays at the parasitic elements are 24VDC Potter and Brumfield with 10 amp contacts.