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The "Bird House Antenna"

(Earl Schlenk-W0ES)



I recently moved into a Condo. As I read the restrictions of the Association, there were 15 pages of rules, 8 of these were concerning antennas!
I wasn't going to let this stop me from having my station up and operating.
Also, this location is in the bottom of a bowl geographically with hills on all side of me.

A flyer came from the association suggesting the residents put up bird feeders  with the provision, that they must be off the ground and be "squirrel proof", again, their quotes. Boy what a bit of synchronicity!

This is the perfect ploy for using their
suggestions to get up a 2 meter antenna.
I enjoy experimenting with Magnetic loop antennas and I have a design that would fit inside a bird house/feeder, and I would build a bird house to enclose it. The dimensions are sized to enclose the loop and I added a roof for appearance purposes and decorative windows and a door.

This article isn't a step by step instruction, but a general concept one.
I will describe the design and control systems, but will leave the construction processes to the reader.

Figure 1.

Figure 1 above shows the basic loop I built using 3 in. wide copper strapping .022 in. in thickness and 6 in. in diameter. This was mounted on a dc motor I bought from "Allelectronics", http://www.allelectronics.com , for about 7 bucks.
I mounted limit switches, using lever switches, to stop the turn motor at its maximum rotation in the CW and CCW directions. I also mounted a home position indicator (for initial loop orientation reference) using an infrared opto-coupler and a LED, see Figure 2 below.

Figure 2. Note: on left side that it says "Turn Motor Voltage"

The capacitor I used was from my junk box and was a 2 to 10pf. The stepper motor was purchased from "Motion King Motor Industry"
http://www.motionking.com, and was mailed directly from China. This was the smallest stepper motor I could find with enough torque to turn the capacitor and have enough resolution (1.8 degree) for the very fine tuning this loop requires. The stepper motor controller was bought as a Kit. I purchased it from "Cana Kit", http://www.canakit.com.


I used a LM350 regulator adjusted to turn the loop at a slow speed.
See Figure 3 below:


Figure 3

The bird house was made from scrap material I had on hand, and I gave the "house" a coat of paint to match the color of the facade of the complex and coated it with 2 coats of Polyethylene. I purchased the "door and windows" from "Doll House Heaven". http://www.dollhouseheaven.com .

The stepper motor is used to adjust the capacitor for resonance on the frequency that you want to use, you can use your SWR meter to tune for resonance by tuning for a 1.1 swr.

The loop is bi- directional and has good nulls off its sides. I mounted the "house" on 1.5 inch diameter PVC pipe 11 foot in the air. It is supported by a 6 foot tall 2x4, attached to landscape timbers that were in the planting area around my patio. I used Belden 8214 coax to feed the loop, running the coax inside the PVC pipe. I used a 10 conductor shielded cable purchased from Allelectronics for the control of the loop and it too, was run inside of the PVC pipe.

The coax and control cable were buried under the mulch in the planting area and ran into the shack through a board mounted in the bottom of the shack window. I am very satisfied with this antenna.

I have received compliments from my neighbors about the "Bird House" and no one knows it is an antenna. I was quizzed as to what the electrical wires were for and I replied that I am going to install a "weather station" inside in the future. This ruse was to explain any future changes I may make or if repairs are necessary in the future. I could also have said it has a camera inside to observe the Birds!

Figure 4 below, shows the loop and it's associated components. Figure 5 shows the finished project!


Figure 4.

Figure 5. Finished "Bird House Antenna:

You could just mount a vertical coax dipole inside of the PVC pipe instead of making a complicated Antenna, such as a loop. I went with the loop antenna because of the low elevation that I live at and I like building loop antennas. You could purchase a Bird House instead of building one and simply mount it on the PVC.

If anyone wants more particulars on building this loop antenna and controls, feel free to e-mail me at: w0es at hotmail.com


I am now in the process of designing a stealth HF Magnetic loop antenna, using some "Fractal" antenna concepts. If this works out I will share the design with you.  73  W0ES


Editors note: Drawings have been compressed. Contact author if more detail is needed.


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