FW: [FoxHunt] Turnstile antennas for 2M

[Kuon & Dale Hunt]

>Good points...
>
>Except when you expect a runner to carry a pair of turnstiles separated
>by a ways. I have run my TDOA BMG sniffer with small loops with some
>success. The LPER is harder to "loopize", but it is possible. Note I
>didn't say it was not possible, but just difficult. I dunno how to do
>the Adcock in H-pole.
>
>Bob, WB6JPI


     The L'Per requires a directional pattern, so two loops
  would have to be phased.  This is actually more common than
  the L'Per method of parasitic coupling, even for vertical
  antennas, since it gives the designer more leeway in mounting.
  The Happy Flyers design in THRDFS illustrates this method.
  Adjusting the phasing line length and antenna spacing should
  give you a suitable omnidirectional pattern.

     The Adcock is even easier:  just mount two identical
  antennas side-by-side and out of phase.  You can do this with
  dipoles, but they will tend to interact due to the overlap
  in elements if the spacing is less than 1/2 wavelength.
  For full-circle DF you need omnidirectional antennas, such as
  small loops or halos, but if you just want an accurate bearing
  over a smaller angular range then you can use dipoles or
  full wave loops broadside to the null direction.  (The problem
  with dipoles is that the pattern has a null in the direction
  of the elements in addition to the usual Adcock null perpendicular
  to the line of the elements.)

     If you use small loops they have to be tuned exactly to the
  same frequency to get the correct phasing.  Generally the best
  approach is to tune the first for maximum signal and the second
  to put the pattern null in the right direction - providing a
  calibrate control.

     Such a system might be interesting to try, but I think the
  yagi would still be better for ARDF for sensitivity, ruggedness,
  and reliability in the presence of reflections. But you could
  build a helmet with a set of small loops or slot antennas around
  the outside, then add a digital readout and course correction
  indicators to a head-up display, and have totally hands-free
  operation...


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