[FoxHunt] DF antennas for HF

[Kuon & Dale Hunt]

Ernie wrote:
....
>
>Now to build some mobile HF DF antennas..... Anybody have some favorite
>designs for those?
>
>


   I have an 80m ARDF receiver circuit submitted to QST that
   is very easy to build.  The loop antenna is 1/2" or 3/8"
   poly tubing bent into a 6" diameter circle.  4 turns of
   wire and about 330pf resonates at the bottom of 80m - it
   is very easy to check with a dip meter.  A one-turn coupling
   loop goes to the receiver or preamp (though 50 ohms may
   load the loop enough to drop the Q pretty low - the input
   resistance should be at least 1K ohms if you want some
   selectivity.)

   I've tuned this up to 40m, but the self-capacitance of the
   loop can make things difficult going much higher.  At that
   point you probably want to use a single turn loop with a
   series capacitor for resonance.  The receiver can be tapped
   up the loop like a gamma match, or taken from a coupling
   loop about 1/5th the size of the main loop.  (If the coupling
   loop is shielded, the rest of the antenna doesn't appear
   to need it.)  Or you can use a balanced FET preamp with
   a high input impedance connected directly to the loop.

   I've used ferrite rods on 80m also, but I found that the
   sensitivity of the air-core loop is much better. Also,
   some ferrite cores work find on the broadcast band, but
   are quite lossy on 80m.  However, a ferrite antenna is
   smaller, and it is easier to adjust the feedpoint
   impedance by modifying the turns ratio.


   Meanwhile, I'll alert the list when the receiver article
   is going to come out.  (We are still proofing the circuit
   board layout.)  Maybe we can convince the League that
   there is a lot of interest in DF projects to make it
   easier to get them published!

        - Dale  WB6BYU