Thursday, August 21, 2014

The Pine Tree HF Stealth Vertical Antenna. Post #289.

Now that Tropical Storm Iselle has left the state of Hawaii, those of us on Hawaii Island can complete the massive task of clearing roads, restoring power, and, in some cases, rebuilding our homes.

Damage to my home was minimal with only fallen trees and "disassembled" wire antennas to be cleared from the property.  Our subdivision in the Orchidland Estates area of the Puna District escaped serious damage with only power interruption and blocked roads presenting major difficulties.

When I surveyed the damage after the passing of the storm (07-08 August 2014), it soon became apparent that most of my "antenna farm" would have to be rebuilt.  The only antennas left intact were the 40/15 meter inverted vee and the NVIS 40 meter loop, which were lowered before the storm.  My 135-foot/41.15 meters doublet lodged in a 45-foot/13.71 meters tall eucalyptus tree was torn to shreds by windblown branches and fallen debris.  I did salvage the 450-ohm ladder line, a few insulators, and about 100-feet/30.48 meters of #14 AWG house wire used for the dipole.

So, I decided to erect an "emergency" antenna until the other antennas could be inspected for damage and later erected on their former supports.

This antenna would have to follow a set of personal rules that have served me well in the past:

The antenna would have to be cheap, using materials obtained locally or stored at my home.  The antenna would have to be "stealthy" and blend in with the environment; and the antenna would have to be multiband, covering, at the minimum, 40-10 meters.

While I was searching for some antenna ideas, I came across an article written by Tony Milluzzi (KD8RTT), who lives in a HOA-controlled community that frowns on amateur radio antennas.  Tony used a backyard tree as his antenna mast and ran a small number of buried radials (16) from the base of the tree.  He ran a length of buried 50-ohm coaxial cable to the basement window of his shack.  With the tree serving as an impromptu mast, Tony had a multiband HF Stealth Vertical that was nearly invisible.  Aha! That's the temporary antenna I needed while I repaired the mess created by Tropical Storm Iselle.

A 60-foot/18.29 meters tall Norfolk Pine Tree about 65-feet/19.81 meters from the garage/shack would do nicely.  The tree was approximately 2-feet/0.609 meters in diameter, with sturdy 3-inch/7.62 cm diameter branches every 2-feet/0.609 meters up the trunk.  I tried a few of the lower branches and they supported my weight of 180 pounds/81.81 kg--sufficient enough to let me climb up the tree and attach the vertical radiator on the trunk of the tree.

After considering the risks of climbing trees in my retirement years, I decided to rely on my trusty slingshot to launch the antenna into the upper limbs of the pine tree.  I just didn't trust my fate to a tree at heights exceeding my body height.  Better safe than sorry.

Next, using the general formula for a vertical antenna (234/f (MHz)=L(feet), I cut a piece of #14 AWG house wire to a length of 33.01-feet/10.06 meters. The wire was cut to the operating frequency of the Hawaii Afternoon Net (7.088 MHz).  I also cut 4 radial wires to the same length.

As with most of my antennas, I built the device on the ground.

Once I had all of the wires cut, I soldered one leg of the surviving 450-ohm ladder line to the vertical element and soldered the remaining leg of the ladder line to the four radials.  All connections were wrapped with several layers of vinyl electrical tape.  I was fortunate to have 75-feet/22.86 meters of ladder line still intact from the storm.

With the completed antenna and radial system on the ground, I attached a ceramic insulator to the tip of the vertical element and then tied a 100-foot/30.48 meters length of nylon cord to the insulator. A lead fishing sinker was attached to the free end of the nylon rope and would serve as a weighted end for shooting the rope into the branches of the tree.

After a few bad shots, I finally shot the rope over a branch approximately 50-feet/15.24 meters above ground.  The remaining length of nylon cord was used to pull the antenna system up the trunk of the tree. The cord was tied off at a nearby tree stump on the lower portion of my property.

The base of the 40 meter vertical was now approximately 17-feet/5.18 meters above ground.

The radial wires were carefully separated and tied off with nylon cord to nearby rocks and tree stumps.

The antenna resembled a ground plane antenna with gently sloping radials.  Because the antenna wire was colored a light green, I could barely see the antenna elements against the tree trunk and the surrounding brush and scrub growth of short trees.

Once the antenna was in position and the radials tied off, I led the remaining length of ladder line to a 4:1 balun (W9INN balun) attached to my garage wall. The ladder line was kept off the ground.  A 3-foot/0.91 meters length of RG-8X coaxial cable went from the balun to the patch panel in the shack/garage window.

A 6-foot/1.82 meters length of RG-8X coax went from the patch panel to the Drake MN-4 antenna transmatch ("tuner").  Short patch cords connected the Ten-Tec Argosy II, low-pass filter, and Heathkit Dummy Load to the Drake MN-4.

INITIAL RESULTS

With the help of the Drake MN-4, I was able to get a 1:1 swr on 40, 30, 20, 15, and 10 meters. Using approximately 20 watts on cw and ssb, I was able to make contacts with fellow hams in my home state of Hawaii, Japan, and the U.S. mainland.  For a quickly assembled antenna, it performed well and on both local and DX stations.  The worst band was 10 meters which was quite noisy throughout the day.  Twenty and 15 meters were fair to good, with 30 and 40 meters doing well after sunset.

This antenna will serve me well until I repair my multiband inverted vee and check out my NVIS delta loop.

Resources:  

Check out the youtube video and posts from Tony Milluzzi (KD8RTT).  Youtube:  https://www.youtube.com/watch?v=Uk8XD7t3P1U.
 http://www.tonymilluzzi.com/2013/10/my-multiband-wire-vertical-antenna.html.

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Thanks for joining me today!

Until next time,

Russ Roberts, KH6JRM.