|Antennas - An Introduction|
|Butternut HF6V Vertical Antenna|
|Butternut Vertical Radial System|
|End Fed Wire Antenna|
|Fan Counterpoise System|
|Radial and Counterpoise Systems Combined - "Ground" System|
Antennas - An Introduction:
The antenna system is the most important part of any radio station. Since antennas often have directional characteristics, many stations have several antennas. At my station I have four antennas:
1. Butternut vertical
2. End fed wire
4. "T" antenna
Which antenna I use depends on the band, the direction in which I wish to work stations, and whether I am transmitting/receiving or receiving only.
If I wish to work DX or work stations in any direction on the 40m, 30m, and 20m, 15m, and 10m bands, I use the Butternut vertical.
For AM broadcast band listening and short wave listening I use the end fed wire antenna.
On 80m and 60m I use the zepp antenna. I also use the zepp antenna on 40m if I wish to work stations to the east or west. If I wish to work stations to the north or south on 40m (e.g. Florida) then I use the Butternut vertical.
On 160m I use the zepp antenna reconfigured as a "T" antenna.
The station also features a radial system for the Butternut vertical antenna as well as a fan counterpoise system for use with the "T" antenna on 160m. Without these "ground" systems the antennas will not work properly.
Butternut HF6V Vertical
Butternut HF6V Vertical:
Butternut Vertical Radial System
Butternut Vertical Radial System:
All vertical antennas need a good radial system to work properly. The "antenna" that we see above the ground is only half of the antenna system. The other half of the antenna system is the radial network, which radiates as much energy as the antenna itself. Simply connecting the antenna ground lead to a ground rod will almost always result in poor performance!. The other half of the antenna system will then either be absent or so lossy that instead of radiating the energy it simply converts it to heat. Likewise, on receive, a substantial amount of the received energy can be lost, resulting in poor reception. If you decide to use a vertical antenna, make the commitment to also provide a good radial system!
For my radial system, I made a circular piece of thick aluminum about 9" in diameter (this could be square too) and then drilled and threaded 36 10-32 holes around the outside. This was then placed at the bottom of the vertical.. I then bought a 500 ft spool of #14 plastic coated stranded wire ("MTW" wire) and laid out 36 radials below the antenna. These are fastened to the aluminum circle with stainless steel 10-32 screws. The antenna isn't at the center of my lot. Instead, it is near one edge. As a result, some of the radials are shorter (maybe only 10 ft long), and some of them are longer (perhaps 40 ft long). The radials are simply laid on the ground and then fastened in place with giant staples called landscape staples or landscape anchoring pins. After a while, the grass grows up around the radials and you can mow over them without any trouble.
Is this the perfect radial system? Probably not, but it seems to work. One final point: Each year you should clean all of the connections with chemical deoxidant and loosen and retighten all of the screws to break through any corrosion and keep the connections sound. Make a commitment to not only install the system but also to maintain the system.
End Fed Wire Antenna
End Fed Wire:
The first antenna that I put up was a simple end fed wire. This is about 70 feet long and runs from the second floor window where the station is located down to a large tree in the back yard. The far end of the antenna is about 6 feet above the ground. The antenna is made of #14 plastic coated solid copper wire. Insulators are used at each end.
I originally used the antenna for both transmitting (with an antenna tuner) and for receiving. Now, however, I only use the antenna for receiving. I normally use this antenna with my Hallicrafters SX-96 receiver for broadcast band (AM) listening/DXng and for short wave listening. I also use it with my Twinplex regenerative receiver and with several other regenerative receivers and crystal radios that I have in my collection. Though it is connected to one of the coaxial inputs on the Palstar Antenna Tuner, I usually bypass the tuner when using the antenna for receiving. For transmitting, the antenna must be worked against some sort of ground or counterpoise system that is connected to the tuner.
For the 80m, 60m, and 40m bands I use a classic multiband Zepp antenna. Another name for such an antenna might be an non-resonant doublet or dipole. The beauty of the zepp antenna is that it is balanced, and doesn't really need a ground connection to operate. (Of course, the ground system is left connected anyway.)
The zepp is fed with homebuilt open wire line with a 3 1/2 wire spacing and a 1 ft spreader spacing.. The length of the antenna or feedline is not critical. The antenna was as long as I could comfortably make it, 120 ft, and the feedline length is whatever was needed for the connection, 27 ft. The antenna essentially runs north and south.
The downside of the zepp antenna is that an antenna tuner with a balanced output must be used to feed it. I use a Palstar AT4K antenna tuner. The Palstar tuners are superior to all other tuners in that they do not place the balun at the output of the tuner, but rather at the input of the tuner. The balun is always operated within its ratings and at its optimum impedance, so there are essentially no balun losses in a Palstar tuner. The entire tuner matching network then floats above ground to maintain the proper balance. To feed unbalanced loads, such as coaxial cable, an end fed wire, or a "T" antenna, one side of the network is simply grounded through a heavy duty relay by pressing a button on the front panel.
On 160m the impedance of a 120 ft zepp antenna is such that even the Palstar antenna tuner cannot accomodate it. On 160m, the two ends of the feedline are connected together to form a single wire which is then connected to the unbalanced output of the tuner, and the tuner is placed in unbalanced mode. The result is a "T" antenna which is then worked against ground or, in my case, an extended radial/fan counterpoise system. In this mode the feedline does not function as a feedline! Instead, it radiates along with the rest of the antenna and the ground/counterpoise system. It must be understood that in such a system everything (including the "ground system") radiates RF and contributes to the radiated signal. Since active parts of the antenna are right at the back of the antenna tuner, there is a lot of RF in the shack, especially when running high power. (But the lower frequency on 160m means that your body won't absorb enough RF to cause any RF exposure problems.) Just don't touch anything metal when transmitting, or you might feel the sting of an RF burn.
Fan Counterpoise System
Fan Counterpoise System:
When I began operating on 160m with the "T" antenna I found that a large ground current flowed into the AC house wiring (neutral and ground wires) and also the house circulating hot water heating system. This current caused interference with the phones, household appliances, and heating thermostats.. On receive, the system picked up noise from all of the devices in the house, raising the background noise on receive by an unacceptable amount.
Since I couldn't disconnect the household ground system from the station equipment, the solution was to provide someplace else where the current could flow. I used a ground rod placed right below the station as a junction point (though the rod itself serves no grounding function) where I could connect several counterpoise wires. These are made of #14 plastic coated stranded copper wire and were run as far as I could in a fan pattern over the yard, as shown in the drawing. They are simply laid on top of the ground and fastened to the ground with landscape staples or anchoring pins.
The ground rod is connected to the station antenna tuner on the second floor with 1/4" braided copper rope (outrageously expensive if bought new!) that a friend gave to me many years ago. It makes for a very low inductance connection to the station.
After installing the fan counterpoise I found that the interference to the appliances and phones in the house was greatly reduced, and that the background noise on receive was also greatly reduced. The counterpoise was definitely worth the time and money needed to install it.
Even with this counterpoise the station is still very hot with RF when operating high power (more than 1kW output) on 160m , due to the proximity of the antenna, which is only 27 ft away. I have to be careful not to touch any metal in the station (like the bug or the antenna tuner roller) when transmitting or I will get an RF burn. No system is perfect!
Radial and Counterpoise System Combined - "Ground" System
Radial And Counterpoise Systems Combined - "Ground" System:
The figure above shows the complete radial and counterpoise system at AA8V. Many would refer to this as the station "ground" system. Even though the radials seem separate from the fan counterpoise, they are in fact connected to each other. The shield of the coax that connects the antenna tuner to the Butternut vertical also serves to connect the radials to the counterpoise. It is a long connection, but on 160m it is short enough that ground current does flow through the coax shield to the radial system. Thus, on 160m, the actual counterpoise for the "T" antenna is the combined vertical radial system and fan counterpoise system.
All of the wires are #14 gauge stranded plastic coated copper wire. None of the wires are buried. Rather, the wires are fastened to the ground with landscape staples or landscape anchoring pins. The grass eventually grows over the wires and they become invisible.
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