EI8IC Home
Click here to view my GuestMap. You can leave your callsign and comments, too !
KB1SG's Rhombic Pages
Home > Rhombics > Build Your Own Wullenweber
This is the KB1SG Build Your Own Wullenweber page. It was written by Ian W. Cummings, KB1SG, and is displayed here with his permission.

Build Your Own CLASSIC BULLSEYE Wullenweber

The FRD-10 is a Navy version of the Wullenweber known as CLASSIC BULLSEYE. This discussion will outline construction details and some specifics of dimensions and the antenna theory behind the CDAA. You may have some trouble building this antenna as the US Government describes costs of between $800,000 and $900,000! Details of the antenna curtain itself is readily available in the public domain. The finer details of the phasing and goniometer circuitry is presumed to be classified as secret. I however think one might be able to make a sector version of the Wullenweber with a reasonable cost associated. Perhaps an arc of 60 degrees with 20 monopoles and the reflector curtain for high band only with the associated ground screen. That would be interesting to mess around with.

The FRD-10 is constructed in two design formats with different dimensions. The original was at Hanza Okinawa and modifications to the design resulted in subsequent differences. These changes were in the diameter of the circles, number of antenna elements, spacing and heights.

The feedlines involved are obviously a big deal here and the feedlines arrive at the central building from 4 sectors (90 degree arcs). These feedlines arrive from both the low band and high band elements.

The low band antenna consists of 40 folded monopole antennas each at very 9 degrees of azimuth. These monopoles atop a base insulator with nonconductive guy wires. There is an aluminum 32 inch crossmember at the top to suspend two parallel aluminum wires adjacent to the mast monopole. The mast is an estimated 60 feet high and about 5 inches diameter. There is a large ceramic insulator at the base. The wires hang off the aluminum cross bar and at their base are resistors to the ground curtain. The mast is fed with a 75/250 ohm transformer and the whole affair ends up being a folded monopole. The feedline is RG-85 A/U.

The low band reflector screen is made up of 80 screen panels (some use 40) located 30 feet or so behind the monopoles. The wires making up the screen are spaced around 1.5 degrees of arc apart resulting in 700 or so vertical wires. They are suspened with 90 foot lengths with insulators at the top and connection to the ground screen at the bottom. They are tensioned and supported by 100 foot wooden poles. Wooden booms span each pair of poles from which the reflectors (and insulators at the top) are suspended.

The high band antenna consists of 120 sleeve monopole antenna elements located at 3 degree intervals of azimuth with a circle circumfrence of 440 feet or so. The monopoles are 25 feet tall and are not guyed. The top monopole is 6 inches diameter and 17 feet or so long. This top section is inserted at it's base inside the bottom section which is 16 inches diameter and roughly 8 feet long. with an overlap of the top section inside the bottom of around 25 inches making a capacitor of sorts. Inside the top section's base is a 25 inch rod with at the top section a shorting disc. The bottom of this rod is the monopole feedpoint. The lower 16 inch section is grounded to the ground screen.

The high band reflector screen is made up of 120 screen panels located around 12 feet behind the monopole circle with a screen circle circumfrence of around 420 feet. The construction is similar to the high band screen. There are around 2,000 wires and each screen is spaced around 11 degree intervals. Each wire is around 25 feet long. Support poles are around 30 feet tall.

Underneath this whole affair is the reflective ground plane. There is a large ring of ground plane made from copper mesh measuring 350 feet at the inner diameter and 500 feet at the outer diameter. Outside this ring are radially disposed ground radials each spaced 1 degree of arc apart extgending from 500 feet out to 650 feet. At the base of each monopole is a copper grounding sheet 8 feet in diameter. Needless to say this antenna has an excellent ground system!

Feedlines are buried en route to the shack and electrical lengths must be carefully controlled and equal. Tolerances less than an inch are important.

The overall principal of this antenna is that the advancing wave front will encounter one monopole first the the two on each side, subsequently the next pair outward and on and on. The feedlines are combined using phasing lines or delay lines that delay the arriving signal such that each monopole output arrives at the receiver simultaneously at the receiver. In effect a circular array is made to perform as if it were a linear one. The reflector screen provides a unidirectional pattern for each monopole with significant gain even before summation using the delay phase lines. The goniometer permits the user to in effect electrically steer the phasing/delay lines by selecting a given arc of monopoles upon demand. The resulting pattern is very narrow and the gain very high. The actual antenna feedlines are capacitively coupled to the goniometer/phasing lines but the details of all of this are obscure.

The low band monopoles use the folded monopole design to create an electrical mirror image dipole element in the ground screen. This makes the size necessary for the monopole around half of what it would otherwise be (over 150 feet for a full sized half wave dipole in the middle of the design frequency). The large diameter mast gives high Q. The wire elements futher augment this electrically. Height is between one eighth wave lengths at 2 mhz and about a half wave a 9 mhz. Impedance is between 10 and 30 ohms.

The high band monopoles also achieves the high Q goal and also uses the mirror image to create a dipole electrically. Similar impedance is likely.

This is all I could glean related to actual construction details. The dimensions are not likely to be exact. Monopole designs are derived from surplus monopole antennas described by others. Scales are from photographs.

 
web design by www.mapability.com --- Irish and international copyright 2000 - 2017