CAUTION

The MicroDipole^TM is a high-Q antenna. The voltage developed at the outer ends of the antennas can be very high. Precautions must be taken to prevent accidental contact with the antenna.

Ground Systems

An RF ground is not necessary with this antenna, but it is good practice to install the best ground system possible for lightning protection and RFI reduction.

GENERAL MOUNTING REQUIREMENTS

The MicroDipole mounts on a 1" mast, which is user supplied. A length of 1" (outside diameter) pipe may be purchased at most hardware stores. A standard 1 1/4" TV mast may be used, but the end will have to be flattened slightly using a vise or hammer. Several MicroDipoles operating on different bands may be mounted on the same pole. Separate feedlines are recommended.

You can mount your MicroDipole almost anywhere. Cliff dwellers, mount your MicroDipole on a balcony or out a window. Put one up on the roof with a TV chimney mount. Hide one completely out of sight in the attic.

The MicroDipole is a wonderfully convenient portable or emergency antenna. Disassembled, it is four feet (4)' long, and it only takes two or three minutes to disassemble or reassemble.

It is a good idea to keep a couple of MicroDipoles handy for emergency work. After all, any serious disaster is going to render most antennas and towers useless. A hank of rope or a telescopic pole, coil of coax, and a MicroDipole will put you back on the air in minutes.

Vacationers -

The MicroDipole is the perfect answer to the special antenna problems you face. The four foot (4') disassembled length and the simple on-site assembly makes it easy to take Ham Radio with you, no matter where in the world you go.

Put up the MicroDipole at night, and drop it down when it can be seen. Hide it in the attic. Sneak it up on the roof. Pretend it's a special TV antenna. If you have 16' of reasonably clear space, you can be on the air with a good signal.

RF GROUNDS AND POLARIZATION

The MicroDipole is a balanced antenna system. This means that RF ground systems and counterpoises are not necessary. Polarization can be changed to either vertical or horizontal simply by rotating the MicroDipole’s mast.

If you plan to operate on more than one band, you will need separate MicroDipoles_TM for each band. You may mount several MicroDipoles on a single mast (6" to one foot apart). Feed each with a separate coaxial cable. There may be some interaction between the antennas. However, it is convenient to have all bands of interest available without having to leave the operating position to change whips.

If the MicroDipole^TM is accessible, use 'Quick Disconnects' to simplify changing the elements when switching bands. With 'Quick disconnects,' a band change is simple.

Band

Typical

Bandwidth

Tuning

Range

Modified

Range

Whip

Length

80

30 KHz

3840 - 4000

Note 1 & 2

40”

40

35 KHz

7125 - 7350

7.0 - 7.2

42 3/8”

30

Full Band

10.1 - 10.15

20

200 KHz

14.0 - 14.4

43 3/4”

17

Full Band

18.06 - 18.16

15

Full Band

21.0 -21.45

37 3/16”

12

Full Band

24.9 - 25

10

Full Band

28.0 29.7

40 1/4”

6

2 MHz

50 - 54

Note 1: 3” capacity-hat lowers resonance to cover 3660 to 3790 KHz.

Note 2: 6 3/8” capacity hat lowers resonance to cover 3500 to 3650 KHz.

Bandwidth: Typical 2:1 SWR bandwidth

Tuning Range: The operating frequencies covered by an unmodified MicroDipoleTM

Modified Range: The available band coverage when the appropriate capacity-hat is installed. Capacity hats lower the resonant frequency of the antenna elements. They are easily installed or removed to allow returning the antenna to its original tuning range.

Whip length: The typical distance the whip extends out of the whip adjustment adaptor.

The MicroDipole^TM consists of two highly efficient mobile whips and a special mount. Mobile whips are used for several reasons. First, they are built to withstand high winds and severe weather. Also, they are very light in weight and they are readily available at reasonable cost. Most importantly, they are efficient.

The Compromises

All short antennas are compromises. A designer can compromise performance or bandwidth or both.

In the MicroDipole I have chosen to trade bandwidth for small size while maintaining good efficiency. There is no reason for building an antenna that produces a wide operating bandwidth and yet is a poor radiator. To the contrary, it makes more sense, especially in limited space applications, to make the antenna as efficient as possible and accept a narrow bandwidth.

Actually, bandwidth is severely limited only on 80 and 40 meters. On most other bands, all, or at least most of the band is available without retuning the antenna. Operating outside the 2:1 SWR bandwidth limits is easily accomplished by either retuning the antenna elements or using a transmatch to achieve an acceptable match at the rig.

The MicroDipole can be an excellent performer. How well it performs depends on its operating environment. Of course, even the best designed system is not going to have the signal of a full-size antenna.

Matching

With any very short antenna system, matching to the low, complex impedance load presented by the antenna is difficult. We solved that problem with our 'Dedicated Matching Units.' Unfortunately, these units are no longer available. Your transmatch is used for matching.

Power rating

When you use a transmatch, you must derate the maximum power delivered to the antenna. Since most transceivers put out about 100 watts, this would be a safe limit under most circumstances. Remember, the SWR on 80 or 40 meters can rise to a very high value as the operating frequency is moved away from antenna resonance. Under conditions of high SWR, coaxial cable can dissipate a considerable percentage of the total power. Keep your coax as short as possible and if the SWR rises above 4:1 or 5:1 before compensation with a transmatch, retune the antenna for a lower SWR.

Modifying the tuning range

The dipole elements used in the ' MicroDipole^TM are high quality mobile whips. They are factory tuned to operate in the voice portion of each band. If you want to operate in the CW portions of the bands, the MicroDipole is easily modified for CW coverage.

Capacity-hats

Capacity-hats are used to lower the resonant frequency of the antenna while maintaining its normal operating bandwidth. Capacity-hats may be added any time and do not require any structural modification of the antenna. They simply attach between the fiberglass resonator and the whip adjustment adaptor.

You can make the capacity-hats yourself. You will need some heavy gauge wire. 12-gauge, copper- clad steel wire is recommended. This wire is available from The RADIO WORKS at nominal cost.

Total Wire

Length

Dimension

“A”

Dimension

“B”

2’

6 3/8”

4”

1’

3”

2 1/2”

Total Wire Length: Total wire length needed to build one capacity-hat.

Dimension "A": Diameter of capacity-hat

Dimension "B": Length of center piece including the 3/4" length needed for bending the hook.

Note: There are two different sizes of capacity- hats. A complete set for 80 and 40 meter CW consists of 6 capacity-hats. Two large-size capacity-hats for 80 meters low band, two small-size for 80 meters mid band, and two small-size capacity-hats for 40 CW.

1. Use heavy-gauge wire. #12 or larger solid copper-clad steel wire is recommended.
2. Cut wire to the total length required. This will be either two feet for a large capacity-hat or one foot for the smaller capacity. For full coverage of 80 and 40 meters, you will need two large and four small capacity-hats.
3. Measure either 4" (large capacity-hat) or 2 1/2" (small capacity-hat) inches from one end of the wire.
4. Bend wire 90 degrees at this point. See the diagram.
5. Form a hook as shown. This hook should be slightly larger than 3/8" across the opening.
6. Bend the remaining length of wire into a circle.
7. Solder as suggested in the diagram.
8. Follow the same procedure for the remaining capacity-hats.

1. Slide the capacity-hat over the whip end of the antenna.
2. Unscrew the whip adjusting adaptor from the fiberglass resonator. You need not completely disassemble the two pieces, just unscrew the whip adjustment adaptor enough turns for the hook to fit.
3. Tighten the whip adjustment adaptor tightly enough to hold the capacity-hat securely in place.

4 To remove the capacity-hat, reverse the mounting procedure.