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Contesting Online Forums : Tips : Interlacing monobanders Forums Help

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Interlacing monobanders Reply
by k4kk on March 16, 2004 Mail this to a friend!
I am looking for experiences with co-mingling monoband antennas on a single boom. I would like to put a small 3 ele 15 meter yagi on the same boom as a 5 element 10 meter yagi. I am planning to do "top and bottom" of boom mounting to create a minimum plane of separation of about 2+ inches. This will be a fairly low height (+/- 50') rotatable antenna. I know that there are some commercial antennas that share a boom but don't know what the issues in design may be. I would appreciate any thoughts or other considerations.
RE: Interlacing monobanders Reply
by K1NQ on March 19, 2004 Mail this to a friend!

Look at this design I did for K1IR. ALL the info is there for you to build a 4 el 15 and 5 el 10m on a 26' boom. Antenna has been in use for 1 year.

It is very hard to do what you are asking. You must be very proficent in modeling and antenna theory. You can not just interlace 10/15m yagi antennas and expect good 10m performance. Very few commerical manufactures of this kind of antenna.

The above antenna works. It has been built and used in 4 contest this year. This is a proven design that I built for K1IR contest station. If you follow the plan and don't deviate by substituting element locations, hardware and taper it will work for you.
If you deviate, then you will nolt be happy with the performance. The antenna uses common hardware. All DXengineering to make it simple.

Dave K1NQ
RE: Interlacing monobanders Reply
by kn2m on April 7, 2004 Mail this to a friend!
I have considerable experience with this topic. It is possible to design a fairly good interlaced antenna. The Bencher Skyhawk is an example of such an antenna. The following concepts generally apply.

1.) More elements add complexity to the antenna model that is like solving X equations with X unknowns. In order to solve the problem, one needs to change element spacing and length in a stepwise process in order to determine which changes are favorable and which are not.

2.) The lower frequency antenna is less affected with gain and F/B with interlacing than the higher frequency antenna. Gain on the lower frequency will roughly be equal to a monoband antenna of the same boom length but computer optimization is still necessary.

3.) A higher frequency antenna can be adjusted in order to preserve decent F/B but it always loses gain due to electrostatic shielding of the larger lower frequency elements.

4.) The gain figure of the higher frequency antenna is equal to at least that of a yagi with one less element on a shorter boom than you are providing it with.

5.) This antenna will model best with separate feeds for each band.

6.) One should consult sources for physical design of yagi antennas in order to properly size and strengthen the elements for wind survival, balance and other mechanical considerations.

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