A Three Band Novice Dipole Antenna
A very nice Novice/Tech Plus antenna can be created by using two dipoles on the same center insulator/balun. Such a 1:1 balun can be easily purchased at places like Honolulu Electronics. The balun can be eliminated if a tuner is used. This antenna will cover the 40, 15 and 10 meter HF bands available to the Novice/Tech Plus operator. Another longer element can be added to cover 80 meters, but it will more than double the size of the antenna.
The top element is the LONG one and works on 40 and 15 meters as shown below. Since 15 meters is the third harmonic of 40 meters, this dipole element will load with the same low feedpoint impedance as a halfwave dipole:
Center Frequency: 7.125 Mhz 21.074 Mhz 3rd Harmonic Halfwave wire dipole is: 65.68 feet 32.84 one side. Low Mount Halfwave is: 64.28 feet 32.14 one side. Halfwave inverted V is: 68.07 feet 34.04 one side.
The bottom element is fanned out at the far end, but connected at the same point in the center as the long element. It is needed because the 10 meter band is not an odd harmonic of either 40 or 15 meters. On 10 meters, the power will go into the low impedance feedpoint of this element and ignore the higher impedance, off frequency dipole cut for 40 and 15 meters. This 10 meter element when cut as a halfwave dipole is:
Center Frequency: 28.300 Mhz Halfwave wire dipole is: 16.54 feet 8.27 one side. Low Mount Halfwave is: 16.18 feet 8.09 one side. Halfwave inverted V is: 17.14 feet 8.57 one side.
So you end up with two wires attached to each side of the center insulator, one about 32 feet 10 inches long and one about 8 feet 4 inches long. You need four end insulators and one center insulator. The end of the 10 meter element should be fanned down about one foot from the top element. It will be electrically ignored at 40 and 15 meters. At 40 and 15 meters the short 10 meter element will be ignored. The result is a simple dipole antenna that will load and work well on 40, 15 and 10 meters.
Somewhat easier to make is 3/2 wave dipole on 10 meters, which is mechanically close to a 40 meter length. It will still have the same low feedpoint impedance. The length of the long version of the 10 meter element is:
Three Quarter wave : 25.65 feet one side
It will have a bit more complex radiation pattern than the 10 meter half wave dipole version, but that can be an advantage in some cases.
Either will work, with the short 1/2 wave 10 meter lower dipole or the long 3/2 wave lower 10 meter dipole. Both use two wires to give three bands of nice resonant operation, one center insulator, four end insulators and four attachment points, but only two end are poles needed, since the attachment points line up vertically.
The wires should be strung up running about north and south for use here in Hawaii. Dipoles radiate broadside! So point them north and south as much as possible and your main radiation will be east and west in a very broad "lobe".
The 3/4 wave on 10 meters will have at least four lobes and could give better coverage on that wonderful band. In fact, the 40/15 meter dipole and the 3/4 wave 10 meter dipole combination may well be the most ideal Novice/Tech Plus wire antenna possible if you have the 70 feet of length needed to install one.
If you can only manage one high central support, you can construct the same antenna as an inverted V. Notice that when configured this way, the length of the wires changes. They have to be a bit longer to resonant at the same novice/tech plus frequencies.