2-El.-6-17m-V. Mk Vl

2-El.-10-17m-25 Ohm

2-El.-10-17m-28 Ohm

3-El.-10-17m-50 Ohm

Test YP-3

Inv.-V/Inv.-U

Dipole, Inverted-V and Inverted-U for portable Operation

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In most cases a dipole has better radiation angles and gain than a simple vertical antenna. Exception is operating on the low bands, where dipoles close to the ground have no DX performance.

For portable operation a height of 10 m can be possible for a dipole for the 10-m-band, built with tapered aluminium tubes. For the following examples we use a 14-MHz-antenna.

The normal Dipole

Impedance is 72 Ohm

Because it is difficult to find to 10 m high places for mounting the two legs of the dipole, it is much easier to use only one mast and an Inverted-V mounting of the dipole. The advantage is that we need only one support, but the disadvantage is the higher elevation angle in comparison with the normal dipole. That means, the DX-performance of the Inverted-V is not so good as we need. The impedance is lower and is influenced by the angle of the wires and the height above ground (35-55 Ohm).
For constructing the Inverted-V the table left has the lengths for a mounting of the antenne top in a heigth of 10 m. The angle between the two legs is 90. The data are for 2-mm-not insulated wires. With insulated wires the lengths are 1-2% less.

Of cause the angle can be greaiter than 90, then the impedance is raising.

The different impedances are caused by the effective heights above ground.

Band

Lengths

Impedance

10 m

2 x 2,62 m

48 W

12 m

2 x 2,96 m

45 W

15 m

2 x 3,50 m

35 W

17 m

2 x 4,12 m

37 W

20 m

2 x 5,26 m

55 W

30 m

2 x 7,24 m

56 W

40 m

2x 10,29 m

38 W

The central part is a tapered dipole for the 10-m-band. On each side 25% of the dipole is bent down. So we come to the Inverted-U with better performance than the Inverted-V.

For the support we need a entral mast, made of glassfibre or aluminium.

For the construction of the Inverted-U see down!

For a comparison of the three antennas I have plotted the azimuth and elevation patterns:

Type

Elevation Main Lobe

Gain

Dipole

29

4,79 dBd

Inverted-V

34

3,16 dBd

Inverted-U

29

4,16 dBd

The table shows the advantage of the Inverted-U against the Inverted-V. All antennas 14,15 MHz, top of the mounting 10 m above ground.

The central part of the Inverted-U-Dipole with a glassfibre tube for reinforcing

The construction of the mast holder and the connection box

The W1JR-current Balun for feeding.

For 3,5-50 MHz the FT140-43 is a good choice. For higher power up to 1 KW a FT240-43 is recommended.

The core is not critical!

I have used PTFE-coax, but RG58 is possible, too.

2x3 turns on an Amidon FT140-66 core.

 

The middle part of an Inverted-U, built by Andy, M0CTR

The construction of the center part. With the given lengths this is a normal dipole for 10 m. For the other bands additional 2-mm-wires are added at each side like the picture down shows.

With the given tapering the dipole has 2x 2,57 m length.

Band

Lengh L

10 m

-

12 m

44 cm

15 m

105 cm

17 m

178 cm

20 m

307 cm

 

For 30 m and 40 m the additional wires are mounted with an angle of 45.

Band Length L

30 m

510 cm

40 m

790 cm