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write your own review of the The Mast Company Vertical Antenna Kit.
Feb 17, 2006 09:13
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Time owned: 3 to 6 months
As a retiree living in a small RV, I operate a full time portable station. Winters are spent in the deserts of the southwest where support structures are non existent along with the attendant problems of propagating a low takeoff angle. I found both problems solved with the 40 meter Vertical Antenna Kit.
The kit comes with an insulated pivoting base that is anchored to the ground with four large drive-in stakes. Guy rings are provided for support. I had to build my own radial system and used 1/8" thick aluminum flat stock, fabricating a rectangular ring around the footprint of the insulated base using stainless nuts and bolts. To this I attached a piece of angle bracket to mount the SO-239. Next I drilled several holes on each side of the "ring" for mounting the radials. I fashioned radials from 18 gauge hookup wire, crimping 4 together to a ring connector. Any type of wire that is easy to work with would work well here.
Initially starting out with four 40 meter radials just to get on the air, I eventually increased that number to 16. At a measured 34.5 feet long the antenna is actually resonant below the 40M band at around 6950 khz, confirmed by my Autek VA-1 analyzer. This brought the feed point impedance up to 46 +j10 after trimming the radials in 3 steps from 33' to 30.5' resulting in a 1.15 : 1 SWR in the CW portion of the band. This also results in a higher SWR in the upper portion of the phone band to where my IC 706 will start to roll back the power above about 7280 khz. To me that's not a problem since I could run it through a tuner in my shack. I've worked ZL, VK, and J lands with this arrangement, with signals reported from 5,5 to 5,7. As a further bonus, this works well as a 3/4 wave vertical on the 15M band providing some additional gain with a lower takeoff angle of about 19 degrees. All fed directly and without the need of a tuner!
Wishing to expand the use of this vertical I built the modified L network featured in the November '05 issue of QST, fed directly at the antenna. After the necessary tuning and tweaking it operated nicely as a half wave vertical on 20 meters with the resultant increase in gain and lower t/o angle. I had another 16 radials for the 20M band from when I was using the vertical shortened as a 1/4 wave and these I added to the setup, but I'm not sure if that was necessary. At least these extra radials would improve performance on 40M. With this arrangement I can switch back and forth between 20M and 40M seamlessly.
Since I operate on 80M with stations in the pacific northwest, I wanted better performance than what my mobile antenna would provide. So my next project was to get it on 80 meters. I started by building a 11.5' capacity hat using 6' pieces of .375" 6063 aluminum tubing sold by Texas Towers. I fashioned a bending jig and, since this tubing is thick walled, I bent one end of each tube to a 90 degree angle, then ovalled that short section with a hammer. This allowed me to construct the cap hat, fastening the tubing using stainless hose clamps around the top of a spare aluminum mast section. I finished it with 14 gauge antenna wire run through drilled holes in the spoke tips. Aside from adding to capacitance the wire also stabilizes the cap hat in high winds and makes for a more robust hat. This proved important, especially when lowering the antenna to change configurations. I added 8 radials of 66' apiece. Next, I hand wound a coil from 12 gauge bare tinned wire , winding to a dimension of 4" long by 3.5" diameter. Using my analyzer I marked 3 separate tap points for portions of the 80 and 75 meter band. Now signal reports are consistently 5,9 into northern California from southern Arizona. One predawn QSO to Aki, JF2VNV resulted in a 5,7 report.
I've even operated as a 1/4 wave on 30 meters using 16 radials cut for that band. What's required is lowering the antenna and removing 3 sections of mast tubing (which eliminates the upper guy ring).
Changing configurations is quite simple for one person. I have three feed methods : directly for 40/15 meters fastening the feed wire with a stainless hose clamp, through the modified L network for 40/20 meters, or through the homebrew inductance coil for 80M. For 80M I have to lower the antenna to install the cap hat, which takes but a few minutes.
Of course, one can always use the antenna as a support structure in itself. I always rig a line to the top guy ring and have used it to hoist inverted Vs, or as one end of a structure for a 21M half square or 6M dipole.
The antenna itself sets up quickly and can be done easily by one person. The only downside to all of this is that it is quite time consuming for one person to set out all those radials. Unless I were to stay in one location for more than a week I would not begin to set it up.
This antenna is not a "plug and play" type. It requires some "project" time, but for those amateurs, like myself, who want to explore and learn this antenna has nicely fit the bill. Now I have a versatile, portable multi band antenna that can produce a decent take off angle without the need for tall support structures.
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