[amsat-bb] Re: Dual band "cheap yagi" question ( interlacing elements?)
Edward R Cole
kl7uw at acsalaska.net
Wed Jun 30 16:35:51 PDT 2010
At 12:19 PM 6/30/2010, Michael Tondee wrote:
>I'm in the process of putting together a portable FM satellite station
>and I intend to homebrew the antenna using the WA5VJB "cheap yagi"
>design. In looking at a picture in the May/June 2007 AMSAT Journal I've
>noticed that the so called "AMSAT demonstration antenna"
> that is composed of two elements on two meters and five elements on
>70cm has the 70cm antenna built completely ahead of the two meter
>antenna on the boom. In other words, the elements for the two bands are
>not interlaced with each other.
> I'm planning to build a larger antenna with more elements as I will
>use it on a tripod rather than holding it by hand and I'm wondering if I
>can interlace the elements of the two antennas on the boom without
>adversely affecting performance. To build the antenna I envision in the
>fashion shown in the picture with one antenna built completely ahead of
>the other on the boom would result in an unruly boom length.
> Also, if I do interlace the elements, should I place them at 90
>degrees orientation to each other as is done in the Arrow design? I
>doubt it makes any difference but just to be clear, I will be using two
>separate radios for TX and RX so no diplexer will be used.
>Yagi antennas, especially dual band designs, are not exactly my forte so
>I thought I'd ask this question just to be sure.
>Tnx and 73,
>Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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I definitely recommend you place the elements at right angles as
there is minimum interaction between the two antennas. Designing a
yagi pretty much requires antenna design software. You will find
considerable interaction doing interlacing and only come up with a
compromise instead of optimized antenna. Arrow and Gulf-Alpha both
use the right angle (or cross polar) design. You can use the simple
WA5VJB design with no fear of one affecting the other. Since you do
not plan to use a diplexer the 20+ dB isolation of this design is beneficial.
73, Ed - KL7UW, WD2XSH/45
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010
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