[TowerTalk] TowerTalk Digest, Vol 37, Issue 55

[Dean Straw]

> Message: 2
> Date: Thu, 19 Jan 2006 09:47:45 -0700
> From: "Bill VanAlstyne W5WVO" <w5wvo at cybermesa.net>
> Subject: [TowerTalk] Interlacing 2M elements on 6M yagi boom
> To: "_Mailing List Tower-Talk" <towertalk at contesting.com>
> Message-ID: <002701c61d18$142c8380$0400a8c0 at billscomputer>
> Content-Type: text/plain;	charset="iso-8859-1"
>
> I have an 18-ft 5-el 6M yagi (two of them stacked, actually).
> This system is an excellent performer, and I don't want to screw
> it up... BUT, I'd sure like to interlace a couple small 2M yagis
> with the 6M elements on the same booms. Feeding the 2M DEs
> separately from the 6M DEs is fine. The spacing between the yagis
> on 6M is fairly close (half a wavelength), so the 2M spacing will
> be about 1.4, not at all a bad number. I know I am going to have
> to get into EZNEC to learn how to model this kind of arrangement,
> but I thought I'd ask first -- is this feasible? Is it a good
> idea? Am I just asking for more headaches than it's worth? Since
> these antennas are on a guyed rotating mast on a 4-ft roof tower,
> I don't want to add any more weight and wind load to the system
> that I have to; otherwise, I'd just put a pair of stand-alone 2M
> yagis between the 6M ones. Ideas, opinions?
>
> Bill / W5WVO

Bill:

I think you will find that the interactions between two Yagis on the same
boom will be serious, leading you to consider stacking separate Yagis -- if
your mast can take the wind loading, of course.

I suggest you take a look at Chapter 18 in the 20th Edition of "The ARRL
Antenna Book." There is an extensive section on stacking different-frequency
Yagis one over the other, starting at page 18-7.

For your situation, should you decide to go with "stacks of stacks" at
different frequencies, there is a section entitled "Stacking Stacks of
Different-Frequency Yagis" starting at page 18-12. The EZNEC models are
included on the CD-ROM that comes with the book and can be modified for your
particular installation.

73, Dean Straw, N6BV
Senior Assistant Technical Editor, ARRL
Editor, The ARRL Antenna Book