The windom dipole antenna was developed around 1929 and its creation is attributed to the radio amateur Loren Windom , W8GZ. Basically it is a dipole fed 1/3 instead of in the center, at this point it turns out that the impedance is the same for the harmonic bands, then with the appropriate balun it is possible to have the impedance adapted for several bands.
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- 1 Story
- 2 Features
- 3 Construction of a Windom Carolina dipole antenna
- 4 Sources
It was originally based on a resonant dipole powered off-center by a single-line transmission line. This single-line power supply is not usually used due to the critical length of the power supply line, its location and the irradiation it produces; but the concept is valid to feed it with balanced lines (ladder) or unbalanced lines (coaxial cables) and a balun with a ratio of 4: 1 or 6: 1, being known in this case as “Carolina Windom”.
The feeding outside the center of the dipole allows it to operate in several bands, making it a multi-band antenna. In practice, what really happens is that at a certain point on the antenna , the impedance is very similar for the band in which the dipole is cut, and its sub-multiples. Thus, a 1/2 wave Windom dipole cut for the 80 meter band can be used in the 40, 20 and 10 meter bands without the aid of an antenna tuner (clipper); with acceptable performance and ROE, but where it works best is in the 40 and 80 meter bands. As in the case of other antennas, there are various opinions regarding adjustments and measurements.
There are different designs with different measurements, taken from different authors. They vary considerably from one to the other, due to the frequency for which the dipole was calculated, the type of balun, its location, height and nearby objects.
The disadvantage of having an impedance of 200 to 300 Ohms has the advantage that it can be used for several bands, without the help of a coupler in which the multiple frequencies have a similar impedance at the supply point.
Let’s take an example, a Windom dipole cut for the 80 meter band, can also work in the 40, 20 and 10 meter bands; and one cut for the 40m band can be used on the 20m and 10m bands.
The impedance of the supply point depends, to a large extent, on the position with respect to the ends, the height of the dipole with respect to the ground, the nearby elements, and whether it has been placed horizontally or in an inverted V. Based on this, if we know what the power point impedance is, we must choose to use a balanced transmission line or an unbalanced one with a balun.
Like any other dipole, the Windom antenna must be adjusted once installed, so the measurements must be taken as a reference and work on them to obtain the best results in terms of ROE and antenna performance.
Carolina windom long version antenna.
Construction of a Windom Carolina dipole antenna
- Here are the calculations for the Carolina windom antenna design cut for the lowest working frequency:
- We take 37.8% for the short side and 62.2% for the long side, totaling half a wavelength for the lowest band in which to operate.
Taking 7,100 MHz as the lowest working frequency
468 / 7.1mhz = 65.9 feet (total 1/2 wavelength).
Short Branch = .378 (37.8%) X 66 = 24.9 feet = 25 feet Long Branch = .622 (62.2%) X 66 = 41.05 feet = 41 feet
Vertical radiator 40 meters / 4 = 10 feet
- For the 80 meter band
468 / 3.7 MHz = 126.48 feet (total 1/2 wavelength) Short branch = .378 (37.8%) X 126.48 = 47.81 feet Long Branch = .622 (62.2%) X 126.48 = 78.67 feet vertical radiator = 80 meters / 4 = 20 feet.
To pass feet to meters, keep in mind that 1 foot = 30.5 cm (0.3048 meters).