Oct 6, 2019

The BWD-90 Folded Dipole

With all of the projects and ideas racing through my head lately, I realized I have neglected to set up the Barker and Williamson BWD-90 folded dipole antenna I got from my dad, K2JGL (SK). I have been very preoccupied with C4FM, MMDVM devices, repeaters, Raspberry Pi computers, WIRES-X, lightning arrestors, grounding, and maybe a few other things. It's time to get back on the air on HF and make some real DX QSO's with the awesome characteristics of the BWD-90 antenna.

Walking through our property looking for a suitable location to set up the antenna, I see this is going to be a bit more difficult than previously thought. The basic site characteristics to setup the antenna would be a flat open space at least 120' long, 50' wide, and 50 ' high. Well, we live in the woods, so that's not going to happen. Guess I'll have to settle for whatever site I can find.

One of the many great benefits of this antenna is the ability to change takeoff angles. My plan is to have the ability to adjust the antenna for several configurations. The following is taken from the Barker & Williamson user instructions.

NVIS propagation is performed as a flat-top with height varying from ground level to approximately 12 feet. This height is dependent on the ground (soil) conditions. It may be possible to lay the antenna on the ground in desert/low water table environments. The B&W NVIS pole kits allow multiple heights. In NVIS installations a counterpoise will sometimes enhance performance. If you are not getting enough distance from your NVIS setup, try raising the center of the antenna a few feet to make a very shallow inverted Vee. (Appropriate NVIS daytime frequencies are approx 5-12 Mhz, nighttime are 2-4 Mhz.) 

Conventional propagation minimum clear height is recommended at 25 feet for operation down to approx 3.5 Mhz (ends 12 feet for inverted Vee or sloper), and 40 feet for 1.8 Mhz (ends 20 feet for inverted Vee or sloper). Less height does not disqualify operation, but may require a tuner on the lowest frequencies. Also, propagation may be reduced with inadequate height on the lower frequencies. 

The next step is to design a support system that includes a left-center-right pulley system so the antenna can be set in any position with the ends from 12' to 24' high, and the center from 12' to 40' high. This would allow everything from a flat-top at 12', to an inverted V at 40' above ground.

More to follow...

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