| 11 Meter Two-Element Helical Beam |
| A 15 Meter version of this antenna appeared in the August 1992 issue of CQ Amateur Radio Magazine in an article written by Bruce Auld NZ5G. |
| In '92, while living on the top floor of a unit block in Sydney and I needed some form of antenna which could be easly set up on a balcony and not be too conspicuous. Not only could this one be used on the balcony but it was small enough to be used indoors as well. One of my first DX contacts was with a station in Hawaii.... with this antenna set up in the living room! The antenna compares well with any 2 element beam antenna, the only compromise being that it has a narrower bandwidth and a lower feedpoint impedance. Constructed using PVC tubing or water pipe which is available from most hardware stores for a few dollars, it can be built in a few hours, and made so that it can be taken apart or assembled within minutes. This makes it an ideal portable antenna which can be taken anywhere. |
| Details of the 11 Meter Mini Beam Antenna are as follows: Driven element: total length of tubing = 251cm Wire Spacing 12mm approx. on 20mm diam. PVC ( note that last few windings are extended towards each end ...see picture below ) Director element: total length of tubing = 206 cm Wire Spacing 12mm approx. on 20mm diam. PVC Boom spacing: 110 cm |
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| This gives some idea of the size of this antenna.... note cup in picture. |
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| T-Section of Driven Element |
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| Since I only use a low power of 50 watts or less, a small 4:1 home-made Balun coil fits nicely in the T-Section. |
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| The last few windings are extended towards each end ... this makes tuning a little easier. |
| Q. How many turns and spacing, how long the wire? There is little point in trying to measure the amount of wire as this will vary too much depending on a number of factors... no two handmade antennas will ever match, and even the measurements given in the article is only a rough guide. The formula: 468/freq in MHz = measurements in feet! .... but be sure to cut the wire just a little longer to start with. Remember that this antenna has a very narrow bandwidth of about 100kHz, so make sure that you tune it close to the calling frequency! |
| Q. If I use something like fibreglass then ok for base installation? See no problem as long as the diameter of the material is the same or very close, and hollow. I used Super Glue to keep the wiring in place before giving it a good coat of yacht varnish! |
| Q. Should I buy a commercial balun? All you need is a good quality RF Toroid ring & heavy enamelled copper wire. You might be able to buy a Balun Kit which would be the cheapest way to go, otherwise there are many Amateur outlets which supply these Balun coils already made up, but you will have to assemble it in some form of box attached to the T-Section or mount it the same as in the notes and seal it. |
| More notes on this antenna coming soon.................. |
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