Antenna

The Antenna

The horn-antenna is made from DuPont foamboard. Although the type that I bought has a reflective Mylar layer on one side, this side is not conductive and plays no role in the collection of microwave signal. Instead, I lined the inside of the horn with heavy duty aluminum foil, and used spray adhesive to hold it in place. NOTE: It is better to use RMAX-3 aluminized foamboard, since this has an aluminum foil coating on one surface already, and there is no need to add your own!) The panels are held together with foil tape. See below.

A rectangular frame, made from 2x2 pine stringers, is glued around the center of mass of the horn. 1/2 inch bolts extend outwards from the sides of the frame, allowing the horn to tilt up and down. Large wingnuts and fender washers allow user to tighten and lock in the horn orientation for desired altitude. There is also a quarter-circle cutout which serves as both an elevation indicator and an additional brace (small C-clamp tightens this.)

In its current state, the horn is not meant for permanent outdoor use. Rain will fill it, animals will jump in, etc. and more durable walls are needed (i.e. sheet metal.) In windy conditions, the frame can be staked down with lightweight twine, using eyehooks on the vertical supports.

Panel Dimensions

This horn is larger than the DSPIRA design. A total of 4 panels (2 sides and top and bottom) were cut from a single sheet of DuPont RMAX-3 aluminized foamboard, The most critical dimensions are the short ends of the trapezoids, which must match the dimensions of the waveguide (paint thinner can.) This horn has a calculated gain of about 100. (Note: the horn shown in most figures on this website is a slightly larger one that I build first)

Reading Altitude

A 1/2-inch plywood 1/4-circle cutout is used for the dual purposes of 1) providing a convenient scale for reading altitude (elevation) above horizon, and 2) locking the horn into a chosen elevation through use of a C-clamp applied between the cutout and the vertical support.

Reading Azimuth

The bottom of the fork pivots on a circular wood platform. The pivot is the grounding rod (1/2" copper tubing-see figure below.) When used on a concrete surface, the ground rod is replaced with a 1/2-inch carriage bolt. Not shown are three thick rubber pads on the underside of the base circle. These sit atop heavy duty tent-stakes when the scope is on a soft surface, like dirt or grass. The stakes can be adjusted to level the platform.

Ground Rod

This serves double-duty as a pivot for the base of the fork. It extends into the ground approximately 10 inches. I use a small jumper cable to connect the top of this rod to a grounding screw on the electronics box.

Filter and Preamp

Signal from the wire antenna goes to a Sawbird H1 Filter (Nooelect, black module on right.) This output is fed to a wideband LNA (silver module on left.) The waveguide itself is a 1 Gallon, F-type paint thinner can with one end removed with a can opener serves as the waveguide and mounting point for the feedwire. This is attached to the inside of the horn using liberal amounts of aluminum foil tape and a few sheet-metal inserts.

Inside of Waveguide

Shows feed wire in the back, vertically oriented and attached to the inside top surface of the waveguide. The feed wire is a 12 Ga copper wire, with its insulation stripped off. The wire is press-fit into the female end of a BNC connector, which is in turn, screwed into the top panel of the waveguide (no soldering.)

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