ANTENTOP- 01- 2006, # 008

Indoor Helical Antenna

By: Igor Grigorov, VA3ZNW

So, my K-1 with 40, 30, 20 and 17 meters bands was successfully assembled and tuned. This one requires an antenna to go to the Air. Certainly, an antenna is a simple thing if... if you live in a private house. But I live in a multistorey apartment building (made from concrete) with huge large restrictions on installation of antennas. The result of these restrictions is those, that I can install an antenna only at a window. Good sign is that in mine apartment the windows are big sized- 150 to 210 centimeters.

My experience on the Air from such premises shows that in this case a magnetic loop antenna is the most effective one. My first choice was the antenna installed at the window. I already have bought a hula- hoop (for antenna itself) and a small stool (for the base of the antenna). However, after I have shown to my YL how the antenna would be looked at its installation place a top of the conditioner (buddy, it looks great!), my permission to antenna installation inside room was rejected by my wife. No one of my arguments to advocate the magnetic loop was accepted.

Other type of an antenna, which can effectively work in my limited conditions, is a helical antenna. Some information on manufacturing and adjustment of the antenna you can find in Reference 1.

So, I began search for stuff for the antenna. Some days back I have bought to my son a Magic Spring Spiral (DOLLARAMA, $1). This Spiral contains 96 coils, each coil has length of 11 centimeters, total length of the wire is 1056 cm. Such length is perfect for helical antenna for the 20 meters band. A wooden stick for open/close curtains (DOLLARAMA, $1) was very suitable for form of the antenna. The stick has diameter in 1/2 inch and length in 170 centimeters.

Design of the Helical Antenna: Photo shows the helical at the window. At first three holes were drilled (one at up and two down) in the stick. Copper wire in diameter of 18 AWG and 15 cm in length was attached to the stick through the holes. Helical antenna was hung up with the help of the wire to an eave. Down part of the antenna was fastened by the wire to a hook. Spiral wire was gone through another hole. Antenna ground was connected to aluminum window frame. My window frame was connected (it was prove by measurement) to the main "ground" (green wire in the main).

Helical Antenna at the Window

Magic Spring Spirale

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