OFF CENTER FEED DIPOLE: A SIMULATION AND A TEST

OFF CENTER FEED DIPOLE:  testing unusual % dimensions

Total length: 21 meters; Off center feed at 25% of lenght (usually we can find 30%)
One leg: 5,25 meters; the other leg: 15,75 meters.
Why 5,25 m? This is not the best %; but for the moment i do not want to cut my vertical antenna aluminium tube. This is a test; if a will have good result i will try to optimize.

You can see minimum SWR at 7 MHz, 14,2 MHz, 21,1 MHz an 28,3 MHz. Using it with a balun and/or wiht an antenna tuner you can easily tune it for these band.
So, i am going to test this antenna with my RIG:

MicroBitx with antenna tuner Kenwood AT-130; the antenna has  a vertical 5,25 meters tube, and a wire of 15,75 meters that is over a tree in his final part.

Today easy contacts on 40 meters, and first contact on 60 meters (with SWR at 1:1.1)

73 de IZ3AYQ

Off Center Feed Dipole: some simulations

Here are some simulations for OCF (off center feed dipoles) of about 20 meters:

The original antenna was developed in 1929 by Lorenz Windom, W8GZ. The orignal antenna was worked against ground. During the years, similar antennas were developed and are generally called Off Center Feed Dipoles. They are simple to build: a simple wire and a balun 4:1 or 6:1, to convert the impedence of 200 - 300 ohm to 50 ohm.
Interesting to study in the Internet: windom, carolina windom, ocf dipole, double windom, balun.


A) L= 20.70 m, L2=6.70 m (L2/L=32%)
The OCF dipole can work (with balun 4:1 or balun 6:1 and tuner) on 7, 14, 28 MHz.

B) L= 20.74 m, L2=6.95 m (L2/L=33%)
Similar to case A): only 3 bands, 7, 14 and 28 MHz.

C) L= 20.1 m, L2=3.7 m (L2/L=18%)
 The OCF dipole can work (with balun 4:1 or balun 6:1 and tuner) on 7, 14, 21, 28 MHz.
We have 4 bands!

D) L= 20.2 m, L2=6.7 m (L2/L=33%)
 Similar to case A): only 3 bands, 7, 14 and 28 MHz.

E) L= 20.70 m, L2=3,8 m (L2/L=18,4%)
 The OCF dipole can work (with balun 4:1 or balun 6:1 and tuner) on 7, 14, 21, 28 MHz.We have 4 bands! This is the best result!

 73 de IZ3AYQ

QRP activity on 20 and 15 meters

This is my QRP soft activity on 20 and 15 meters, from the 2 of february to the 23 of june 2018: with a RTX  microBITX, and vertical dipole 6 meters from the ground; a QRP and very simple and small station !

73 de IZ3AYQ

Simple dual band antenna for 145 - 431 MHz - Pattern study

Pattern study using the software "EZNEC"  V6 free by W7EL

Ideal situation (dipole in free space):

At  145 MHz; this is the classic diagram of an half wave dipole:

At 431 MHz; this is a diagram of a 3/2 lambda dipole in free space:

But if you put the dipole in vertical polarization, 3 meters from the ground you che see this:

For the half wave dipole at 145 MHz:

For the same dipole at 431 MHz:

In both case maximun gain in low in the horizon and, yes this antenna is not for DX, but it is a simple, cheap and usable antenna.

73 de IZ3AYQ

The simplest dual band antenna for 145 and 431 MHz

73 de IZ3AYQ