June 14, 2010:
I have since moved out of this house, and all antennas have been removed (so sad!).
Updated October 4, 2009
All of my antennas are located on the dock behind my home. I live in privately managed US Navy housing, and I avoid dealing with their policies by placing all the antennas on the dock, of which they claim no ownership to isolate them from any EPA concerns. This is a winning situation for me, as I can take advantage of salt water enhancement and not have to worry about any harassment from the housing office (only the tall vertical is visible from the street, and it is difficult to see). My neighbors are great - very supportive - but it helps that I do not have any interference issues with any of them.
First, my “big” vertical, used for 160 and 80m.
This is a photo of the vertical itself, which is 54 feet tall. It’s built from the skeleton of a butternut HF9V, with additional telescoped aluminum elements and a base insulator of 1.125″ fiberglass rod. The antenna is quite floppy in the wind, and I designed it to be light enough to be easily laid over in case of hurricane preparation (necessary 5 times in 2008). It’s guyed at one point, and while the tip folds over quite a bit in the wind, it has held up well in 50mph gusts. I can raise and lower this vertical by myself in about 5 minutes.
This coil brings the antenna into resonance on 3.5 Mhz. I can tap the coil wherever I need to match it anywhere in the 80/75m band.
Here is the 160m loading coil, made from refrigeration tubing. A vacuum relay is used to bypass the loading coil, so I can remotely switch between 80 and 160m. The hairpin coil brings the impedance up to 50 ohms for 160m; leaving it in line on 80m causes a slight mismatch, 1.2:1 SWR, which is negligible. I use one elevated radial for each band, which “couples” the antenna to the salt water. I see no difference in impedance or real-life performance with additional radials. The elevated radial concept eliminates the problem with SWR fluctuations due to tidal change.
Below is the feed point of my 40/30m vertical. By using parallel radiators, I get two bands in one antenna. Adding a 3rd band (with a third radiator) is possible, however getting the third (highest frequency) band to match is very finicky. There are two elevated radials for each band.
Below are two pictures, the first showing the feed point of one of my two 20m verticals (fed as a phased pair, 1/2 wave spaced, fed in or 180 degrees out of phase). Under the bucket in the second photo is the switching network. The random coiled cables are the delay line, 12:1 transformer (I used 50 ohm coax to each vertical), and coiled up extra feed line running toward the shack that I didn’t want to cut!
One thing - after two years, the blue bucket has become so brittle that I can barely handle it without chunks falling off. Tropical sunlight has taken it’s toll! Also, each vertical had two elevated radials for a total of four in the system.
Below are two photos showing the 17/12m verticals. This is a similar setup as 40/30. There are two elevated radials for 17m, but only one for 12m. I was unable to get 12m to resonate unless I placed the radial perpendicular to those for 17m.
And here is a lowly vertical dipole in the trees for 10m if that band ever pops open again
Looking back toward the dock at the back of the house. Hiding in the trees is a 15m half square antenna. You can see the “Waller Flag” low band receive antenna camouflaged against the trees.
And looking the other way (toward the South East). In the foreground is the Waller Flag receive only antenna. It consists of two flag type receive antennas, inline, fed 180 degrees out of phase. It’s performance is outstanding on 160 and 80m.
One of the HF9V coils works well to bring resonance into the CW section of 80M. The vertical itself is resonant at about 3770khz, so with the clip lead I can easily change between the CW and SSB segments of 80 meters. On 160m, the bandwidth is very limited at about 20 khz. This clip lead also allows me to change the resonance point from between 1825 to 1880 Khz on 160 meters. Normally, the coil is fed as is, and the antenna is resonant at 3510 and 1825 Khz, depending on the relay position.
The big vertical has two radials, one for each band. Radial length is critical, and small changes in length result in big changes in resonance point. I’ve attempted feeding verticals with radials in the salt water, however I was always disappointed in their performance. W8JI has written about the skin depth of salt water at HF frequencies, which is inches. Any wire deeper than this point ceases to act as an RF ground, and is wasted. AA7JV has had lots of sucess from his home and on DXpeditions by using a base loaded remote tuner to adjust for variations in SWR due to tidal fluctuations with submerged radials, however the elevated radials I use offer me outstanding performance. Each vertical I use has one or two elevated radials as you can see in the image. This system is modeled after K2KW’s “Team Vertical” expeditions to Jamaica and elsewhere, so their effectiveness has been proven.
These two images show the meat of the feed system. The antenna is base loaded for 160m, and I made the coil with 1/4″ copper refrigerant tubing. Approximately 2/3rds of the coil is necessary to bring resonance to 1825Khz. There are two vacuum relays. One relay bypasses the 160m coil to directly feed the antenna as an 80m vertical, and the other relay switches in a hairpin match to bring the vertical’s impedance up to 50 ohms when in the 160m position. Without the hairpin match, the antenna shows about 12 ohms impedance at 1.8 Mhz, presenting a high SWR to the radio.Start Slide Show with PicLens Lite
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This post was written by admin on February 6, 2009