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Trader's Net (Carolina Windom)

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Barry
Trader's Net (Carolina Windom)

Len Carlson N4IWL's article on a "New Carolina Windom" is the basis for some of the information I will base Thursday night's discussion on. He first explains the original Windom developed by Loren Windom around 1929. His article states: 

The Original Windom, as I will call it, was the first known design of an off-center-fed antenna designed for use by amateurs on the ham bands. Its characteristics made it possible to use one antenna to cover all of the harmonically related ham bands. One of the drawbacks is that it requires an antenna tuner and a very good ground system. Although in those days with vacuum tube transmitters and receivers this was not a particular disadvantage. Figure 1 is a graphic representation of the original Windom. See attachment for figures.
 
The original Windom was 130 feet long with a single-wire feed line connected approximately at the 600-ohm impedance point on the radiator. The feed line also acts as a radiator. The original antenna was designed to be used on 80 meters and all of the harmonically related bands (40, 20, 15, and 10 meters) using an antenna tuner between the transmitter andPage: 2 QRP Expressions the single-wire feed line. The feed point is 37.8% from one end of the radiator. This was where Loren Windom calculated the 600 ohm feed point would be located. Figure 2 is the electrical equivalent of the Traditional Carolina Windom
 
The Traditional Carolina Windom: Figure 3a is the true representation of the Traditional Carolina Windom antenna. The main haracteristics are: (1) It is 66 feet in length and designed to cover the 40, 20, 15, and 10 meter bands without the need for a tuner; (2) It will also work quite well on 17 and 30 meters with a tuner; (3) it requires a 4:1 Balun at the transmitter end on all-bands except 15-meters and a 1:10
Balun/choke when working 15-meters. This antenna works very well and achieves excellent signal reports when up 24’ or higher and then trimmed and tuned to frequency. You simply need to cut the antenna (always keeping the 37.8/62.2% ratio to the feed point) to frequency using the MFJ-259B or similar test equipment.
 
The feed line from the radiator is 300-ohm twin lead or 300-ohm ladder-line (which is lighter and can be purchased at many hamfests). The twin lead must be cut to frequency for 15-meters. Its length must be an odd-multiple of a ¼ wave on 15-meters. To make that simpler, ¼ wave (in feet) at 21.060MHz is approximately 11 feet therefore the 3rd multiple is 33 feet and the 5th multiple is 55 feet and so on. I chose 55 feet since that was close to reaching my shack from where the antenna was hanging. Figure 3a shows a pictorial of the Traditional Carolina Windom. The 300-ohm twin lead actually is the primary radiator on 15-meters. As such, a choke or 1:1 Balun is used between the 300-ohm twin lead and the 50-ohm coax to the transmitter. A 4:1 Balun is required for the other bands in order to match the higher impedance of the antenna on 40, 20, and 10 meters.
 
The New Carolina Windom: Figure 3b is a pictorial of the New Carolina Windom.
This more recent version has some very interesting characteristics. For one, the 4:1 Balun has been moved to the antenna radiator and is built into the center insulator. The other interesting feature is the 10 feet of coax from the Balun and terminated in a choke or line isolator. I have fitted the 10 foot stub with PL-259 UHF connectors on each end. This allows the coax vertical radiator to be easily removed if desired. It is designed to hang vertically which is one reason why this antenna is so effective. Look at the radiation patterns later in the next column. The radiation pattern when using the vertical radiator combines both horizontal and vertical radiation components and lowers the effective angle of radiation.
 
The antenna can be used without the vertical radiator but the radiation pattern will lose the low angle component and may make the antenna less effective. If the vertical radiator is removed then you should move the line isolator to the bottom of the balun.
 
This antenna should not need a tuner on the 40, 20,15, and 10 meter bands although you may use one if you feel the need to. It will operate on 80, 30, and 17 meters but will require a tuner for these bands.

The article goes on to demonstrate how to build the balun for the antenna.

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