A 6 Band Vertical Antenna

The vertical antenna described here preforms admirbly on six (6) bands. It could be extended to cover more bands, but at the time six was my target goal. This was before age of 2,200 meters, 630 meters, 30 meters, 17 meters and 12 meters. It was also before the age of digital cameras, hence the lack of actual pictures. Only three pictures exist of of the antenna components and they cannot be found.

As to performance, this antenna exceeded expectations on all bands. From the start, it covered 160 meters, 80 meters, 40 meters, 20 meters, 15 meters and 2 meters. Two years in a row, this antenna won the ARRL 160 meter contest in Oklahoma. More years could have been won, but I only competed those two years. Alaska, Vermont, Maine, many Canadian including Nova Scotia, Mexico and a few DX countries were worked on 160 meters. I consistantly worked over 100 mile radius with 5/9+ signal reports on 2 meters.

The antenna should be put on 2,200 meters, 630 meters, 30 meters and 17 meters by changing the taps on the loading coil. Or better yet, getting a bigger bandswitch and adding these to the antenna and having a 10 band antenna. Adding 12 and 10 meters will require some experimenting with the matching network.

All of the graphs presented were calculated using EZNEC antenna software written by W7EL. Except for 160 meters the graphs are calculated for frequencies that are even increments of the midpoint of the 20 meter band, that is 14.15 Mhz. The 160 meter band was calculated for 1.85 Mhz to allow coverage of the bottom 100 Khz of the 160 meter band. That is the beauty of this antenna system. The only bands that require a critical antenna length are 20 and 40 meters. When tuning the matching networks, be sure and tune 20 and 40 meters at the designed antenna length. Tune all the others for your favorite frequency.

The matching network was tuned using a homebrew antenna analyzer. The two meter jpole was also tuned using a homebrew VHF antenna analyzer. Output was measured useing a homebrew field strength meter. Nothing scientific, just driving around and seeing any problems could be found. None were!

Before you get excited, there are a couple of real drawbacks to this antenna. First, there are two runs of coax, one for HF and one for VHF. Second, you have to run outside to throw the band switch. Third, you have to remember to check the knife switch while out there, it is switched off on 40 meters. And fourth, most of the matching network components were purchased cheaply at auctions and surplus shops. However, even buying new components, this shouls be the cheapest best antenna you can build.

The basic antenna is a simple 20 meter 5/8 wavelength vertical. I used seven (7) radials alternating between 20 meter and 40 meter radials. I have not specified length of the vertical in linear measurement since each construction site has to select material and apply the appropriate velocity factor.`

Six (6) radials were used alternating between 40 meter radials and 20 meter radials. The antenna was erected at the corner of the house, so one quadrant did not have a radial. Also, one radial running parallel to the house was tied into the rebar mesh of a very large patio before the concrete was poured.

The upper part of the 20 meter 5/8 vertical is made into a 2 meter jpole antenna. RG-8U coax is fed up through the 20 meter 5/8 vertical and brought out through a hole to feed the two meter jpole matching section. A conducting standoff attaches the 2 meter matching section to the main 20 meter 5/8 vertical antenna. An insulating standoff holds the matching section steady. In my case, the 20 meter 5/8 vertical was made from 1.5 inch TV mast sections. The 2 meter matching section was made from half inch electrical conduit.

The matching network consists of four main parts. The heart of the network is the coil. A military surplus coil wound on a ceramic core about 2 inches in diameter and 8 ten inches long was used. A surplus heavy duty bandswitch from an antenna control box was used for the band switch; and yes, it only had five posistions. The tuning capacitor was salvaged from a gutted ARC5 transmitter and was about 150 mmfd. The knife switch was one of those old fashioned manual throw switches with a pivoting arm on a heavy ceramic base. The arm had an insulating handle. You simply grabbed the handle and pulled it open, or closed it. It was left over in my junk box from childhood.

The coil acts as a loading coil on all bands except 40 meters. The knife switch shorts out the unused portion of the coil. In my case, 40 meters needed only capacitve reactance for matching, so only the capacitor is used in the circuit. The knife switch has to be opened, or the capacitor is shorted out. A run of RG8U coax was used from the matching network to the transceiver.

The entire matching network was housed in a wooden box with an access door. The box used bottom openings for ventalation to reduce sweating.

The elevation plot shows maximum gain of -1.64 dBi at an angle of 25 degrees. Of more interest is the beamwidth of 47.2 degrees between the -3dB points of 7.4 degrees and 54.6 degrees. The antenna gives outstanding low angle performance on 160 meters.

Looking at the 3D donut plot, the antenna theoretically displays a perfect omnidirection pattern with no nulls. In the real world, this can not be true due to a plethora of factors; house effects in one (x,y) quadrant to start with and an inadaquate radial system to mention only two. Actual performance and field strength measurments (though sparse and not a scientific study) leads one to believe that including the rebar mesh of a very large patio in the radial system helped cure some of these problems.

The elevation plot shows maximum gain of -.76 dBi at an angle of 26 degrees. Of more interest is the beamwidth of 46.2 degrees between the -3dB points of 8.5 degrees and 54.7 degrees. These figures are very similar to those on 160 meters except for increased gain factor of -.76 dB. Real world performance showed surprising good results.

Looking at the 3D donut plot, the 160 meter comments apply.

The elevation plot shows maximum gain of -.11 dBi at an angle of 24 degrees. Of more interest is the beamwidth of 40.8 degrees between the -3dB points of 8.6 degrees and 49.4 degrees. These figures are very similar to those on 160 meters except for the gain factor of is coming up to -.11 dB. Real world performance showed this gain increase.

Looking at the 3D donut plot, the 160 meter comments apply.

The elevation plot shows maximum gain of 1.81 dBi at an angle of 16 degrees. Of more interest is the beamwidth of 53.0 degrees between the -3dB points of 6.3 degrees and 59.3 degrees. These figures are very encouaging, especially the highest gain factor of 1.81 dBi and a usable 6.3 degree low angle radiation. Real world usage showed the improved performance.

Looking at the 3D donut plot, the 160 meter comments apply.

The elevation plot shows maximum gain of 3.75 dBi at an angle of 37 degrees. Of more interest is the beamwidth of 31.1 degrees between the -3dB points of 22.1 degrees and 53.2 degrees. These figures are very encouaging, especially the highest gain factor of 3.75 dBi, but the high angle of radiation ia a real disapointment. Real world usage has been limited.

Looking at the 3D donut plot, the 160 meter comments apply.

LINKS