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15/20/40m WIRE DIPOLE "UN7JOT"

I built this antenna in January 2008,while I was on the air from Kazakhstan as UN7JOT.

Since I was mainly interested in the 20 and 40 meters,I came up with a simple antenna,made with common materials.

To keep things simple,I choose not to use a balun,but I opted for a choke,made from coax cable,easier to build.

For the center insulator I've used a plastic cutting board,strong enough to support the weight of the structure.

The choke was built over a plastic bottle.

To calculate the length of the elements,I used the formula

TOTAL LENGHT OF DIPOLE (in meters) = 142 / f (frequency in MHz)

the result must be then divided by 2, giving the lenght in meters of each one of the elements.

In my case,since I was mainly interested in the digimodes,I choose to calculate the elements for 14.080 MHz and 7.040 MHz.

The 40m element can be also used on the 15m band (3rd harmonic: 7 MHz * 3=21 MHz)

The cutting board (made in China),ready to become the center insulator of the dipole

The center insulator,already drilled and ready for the installation of the choke and the dipole elements

The coax choke,built over a pipe from a plastic bottle

the building details:

diameter 9 cm

length 11 cm

number of coils 21

cm of coax cable per each turn 31 cm

total length of coax cable required for the choke 6,5 meters

Another view of the choke

Detail of the coaxial cable (made in China),the dimensions of this cable are the same as RG58 [PAGE 2>>]