Saturday, July 30, 2011

Contest Station AA1K

Tower 2, 97 feet Rohn 45. Click for large image.
3-stack of 204BA, 3-el. HyGain 40m yagi, 5-el 10m yagi

    Towers and antennas

There are currently six Rohn towers.

Tower 6 and Tower 1
Left: 3-el Hy-Gain 40m yagi; Right: 5-el. 6m over 5-el 10m

Tower 3, 97 feet Rohn 25. Click for large image.
15-meter stack at 98/65 feet

Tower 1, 97 feet Rohn 25. Click for large image.
The 160-meter series-fed tower. 4-el 6-meter yagi on top.

Tower 1
Tower 1 is 97 feet of Rohn 25. This tower has a homebrew insulated base using three large ceramic insulators. They are about 8-inches diameter and a bit of overkill -- one would have done the job. To test their load I drove over an extra one that was cracked with my Jeep several times with no damage done.
This tower is series-fed as a vertical on 160 meters. For top loading, there is a 4-element 6-meter yagi, a recently added modified HyGain 105BA for 10 meters, a long 220-mHz yagi for the PacketCluster node backbone link, and a couple of phased 2-meter verticals for the PacketCluster user frequency. A small LC network at the base brings the tower into resonance around 1830 kHz.
A 1/4 wave wire for 40 meters is hung off the tower and works quite well as a backup to the 40m beam on another tower.
Large coils of coax or small hardline are wound on 6-inch PVC forms to serve as RF chokes on the feedlines and rotor cable going up the tower. These are placed right at the base. I could have eliminated these by shunt-feeding the tower but I wanted to be able to easily "float" the tower to enable tuning of the parasitic elements. Thanks to Tom, W8JI, for the RF choke idea.
Sloping T-shaped parasitic elements for 160 meters are hung off the top of the tower, supported by rope catenaries. These are spaced out 66 feet to the NE, SE, SW and NW, giving us a switchable 3-element parastic array in four directions. This project is still under construction -- so far I have the NE/SW elements and the SE element in place. For more info on this K3LR array see ON4UN's Low Band Antennas book.
Two more elements toward Europe will be added soon to give us five elements in that direction.
There are 120 radials coming off the center driven element, and 120 radials coming off each of the parastic elements. These are 1/4 wave radials or as long as it takes to meet buss wires midway between elements.Radials are mostly No. 12 insulated THHN stranded wire obtained from a local scrap yard. Some are No. 19 enameled wire.
The tower is located in the middle of a small grove of about 20 loblolly pine trees that are about 70 feet tall. Guys are a mix of Phillystran and EHS steel with insulators.
Tower 2
Tower 2 is 97 feet of Rohn 45. This holds a stack of Hy-Gain 204BA 4-element 20-meter yagis at 33, 65 and 98 feet. Only the top one rotates (on a Tailtwister rotor); the lower two are fixed on Europe. A relay box at the base of the tower allows remote selection of any combination of the antennas.
A Hy-Gain Explorer 3-element yagi is at 83 feet on a Ring Rotor.
A 440-mHz Quagi is at 95 feet to provide a link for the W3PP PacketCluster node near Laurel, Delaware.
A pair of 8-element KLM 2-meter yagis are at 93 feet, aimed at the Frankford Radio Club repeater on 147.27 mHz, north of Philadelphia.
Tower 3
Tower 3 is 97 feet of Rohn 25. This holds two Wilson 15-meter yagis, model 415-M. These are four elements on a 17-foot boom. They are placed at 98 feet and 50 feet, though I plan to move the lower one to 65 feet soon.
An inverted Vee for 80 meters hangs from 95 feet.
Tower 4
Tower 4 is 99 feet of Rohn 55, installed in the winter of 2004-2005, and will eventually hold a stack of 40-meter beams.
Tower 5
Tower 5 is Rohn 25, an experimental expansion for the 160-meter transmitting array, offering an additional director toward Europe.
Tower 6
Tower 6 is 64 feet of Rohn 25 sitting on insulators, serving as a driven element for an 80 meter parasitic array. Still under construction.
Other antennas
A homebrew 5-element 10-meter yagi on a 26-foot boom hangs at 15 feet from a loblolly pine, fixed due south to fill in the "shadow" of the side-mounted 10-meter yagi on Tower 2.
A rope catenary at 80 feet between Tower 1 and Tower 2 supports a 2-element delta loop parasitic array for 80 meters, switchable NE/SW.
Numerous Beverage antennas for receiving are described on another page.

Base of Tower 1. Click for larger image.
RF chokes isolate feedlines going up the tower.

Click for larger image
The ceramic base insulators on 160m tower.

Click for larger image
Each insulator measures 7" diameter by 7.5 inches long; threaded metal flange is on each end.

Click for larger image
The posts sticking up from lower plate end about 1" below top plate.

New tower serves as 2nd director of 160m vertical
This is 2nd director toward Europe. 90 feet tall with small loading coil at base.

Click for larger image
This is a spark gap for lightning protection. No sign it has ever been used.

Click for larger image
A pair of 80-meter delta loops are hung from a catenary between Towers 1 and 2. Apex about 70 feet.

Base of NW parasitic element, 160m array
The coil makes this element resonant about 1780 khz to serve as a reflector for SE.

Click on photo to enlarge
Elevated guy posts. For Rohn 25 Tower 1 in foreground, for Rohn 45 Tower 2 at rear.

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