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I need to create a setup where I have three radio transceivers (869.4MHz) setup in a straight line.

I need to be able to communicate, in both directions, from the centre pole to the outside two poles, and back.

I had planned to use yagi aerials but, whilst that's fine for the two outside poles, it means my centre pole has an issue as it could only face in one direction.

So, I guess I now have 3 options:

  1. Revert to an omni aerial in the middle
  2. Use two separate transceivers, each with its own yagi aerial, facing one in each direction
  3. Attaching two yagi aerials to a single transceiver

Is 3 actually viable?

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  1. Two Yagi antennas on the same antenna port could work for this application.

    • Join the feed lines from the two antennas with a power divider for proper impedance matching.
    • Make sure that they are mounted in-line with each other with the two driven elements some multiple of a whole wavelength apart. This ensures that the rearward radiation of one won't partly cancel out the other.
  2. Alternatively, you could design a single antenna which radiates in both directions. This is an uncommon application so you might not find one off the shelf, but antenna modeling software can help you verify a design before building it.

    The simplest design I can think of for the purpose is an array antenna, which contains multiple identical elements. Depending on the phasing and spacing, a row of vertical dipoles could radiate either perpendicular to or parallel to the line; often there is a reflector but you would omit that.

    It's also possible that an antenna designed like a Yagi (single driven element) but with two sets of directors instead of a reflector element would work well.

  3. You might find that a simple dipole antenna at the center and Yagis at the ends give you an adequate link.

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Merely trim the reflector element of one yagi to the length of the first director and it will become bi-directional enough to get the job done without the expense of another yagi and harness. Some retuning of the gama match may be needed

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  • $\begingroup$ Welcome to this site, Jim! This seems to me to be a great idea, though I haven't modeled it. :-) $\endgroup$ – Mike Waters Nov 29 '18 at 17:10
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Yagi antennas typically have a large back lobe. Their front to back ratio is always much larger than their front to side ratio. It is not uncommon to make contacts off the back side of a yagi. (Or start a contact that way and flip to get a better signal.)

So, one option would be to install a single yagi on the pole and test if you can reach both sites. If not, flip it and test again. If one site is closer than the other, this might work well.

That failing, you could build a bidirectional three element yagi with a driven element between two directors (as suggested by Jim Navotney above), or a two element yagi with two driven elements and an antenna switch to flip between them...

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