This antenna was designed with Florida weather conditions in mind. The winds tend to be below 60MPH most of the time, and those generally are short lived from storm cells and microbursts. When the hurricanes come there is enough lead time to lower the antennas. I have a full size 80M vertical, and it is 3 hour job to lower it. This antenna can be lowered in about ten seconds. When the hurricane comes time is at a premium to batten down the property, so this antenna is ideal for this application. I hope to erect a 4 square of these antennas and it is a very practical solution to hurricanes. We do not get ice and snow. I believe the Spiderpole would handle ice without problem, but I doubt the aluminum would without guying.
If I guyed it I would not guy it above the aluminum, but just below where the Spiderpole begins. Guys will impart a downward force on the mast toward the ground and will tend to try to collapse the pole.
The antenna performs very well. I have a full size 80M on a different part of the property, and after A/B test between the full size and this antenna there is virtually no difference in performance at receiving stations. The antenna exhibits similar bandwidth. I can tune both CW and DX-SSB (3.5-3.8mhz) portions of the band with under 2:1. The antenna is resonant around 3600, and the SWR is less than 1.7:1 from 3.5 to about 3.8mhz. The modeled base impedance of the 54ft antenna is 27 ohms at 3.5mhz and 34 ohms at 3.8, with an average of about 28 ohms near resonance. At full legal power the antenna behaves like a dream. There is no quirky-ness in how it tunes, or evidence of heating. The resonance can be raised and lowered easily by adjusting the length of the coil.
My full size antenna has an impedance of about 36 ohms. My Butternut HF-2V had an impedance of about 9 or 10 ohms at resonance, and this antenna has about 30 ohms. Over a 13-15 ohm ground screen (16 1/4 wave radials) the calculated relative efficiencies are 75% full size, 70% for the 54footer, and 44% for the HF-2V or about 2.3db. between the larger antennas and the HF-2V.
The antenna is also resonant on or near 30M. My antenna shows a 2:1 SWR on this band. It should exhibit something like a 5/8 wave pattern on 30. This antenna can be made multi-band by adding a thin light cross arm just below the coil and running a 40M 1/4 wire from the base up to the cross arm and then to an insulator coming off the spiderpole. The biggest need to is steer clear of the coil, otherwise there is little interaction between the 40M wire and the 80M antenna. The 2 elements are fed like a fan dipole, with each connected to a common fed point. There is a technique that was published by Gary Breed K9AY (of the low band loop fame), which uses an element that is mutually coupled to the fed element such that it is resonant on the band of interest, but not connected to the feed point. This is an example of an antenna designed in this manner. I prototyped this type of feed with this antenna and found it accepts power just as well, and seems to work as well as an element connected directly to the feed point. This technique has a slightly narrower bandwidth than the direct feed method, but if I was considering making this vertical cover many bands instead of just a couple I would strongly consider this technique. This technique shows a better pattern than the direct feed method in my modeling program, but I am not sure that isn't an artifact of the model. If you try this technique cut the wire a little longer than you might predict from the formula 234/f mhz. My concern about adding a lot of elements is weight and wind load on this antenna, but for very little additional weight and load you can have 80, 40 and 30 without the need of additional feed lines or switches. This technique may work well if you were to use multi wire ribbon cable such as the 4 wire Radio Shack rotor cable. This would give small weight and small a wind footprint and the possibility of 4 extra bands.
So for about a $200-$250 dollar investment depending on the junkbox, you can have a 80, 40, 30M antenna that is highly effective for this period of the sunspot cycle. Since it can be raised and lowered in a heartbeat it may even be useful for the person with covenant problems. Flip it up just prior to sun-down, flip it down just after sun-up and work DX like crazy in between.
Suggestions are welcome at:
