[FoxHunt] DF antennas for HF

[Kuon & Dale Hunt]

Bruce contributed:

>
>Dale's design is very clever in only shielding the coupling loop. I am going
>to try this technique myself very soon.


    I can't claim credit for the design - I just looked through
    my books and found something that would be easy to copy.


>I can attest that the directionality was fine at the German Championships
>(even if the sensitivity of the reciever was a little down).

    Well, maybe it would have worked better if you hadn't bent
    the plates of the tuning capacitor.   :-)


>
>Dale, I take it that the necessary break in the shield is effectively at the
>connection point (instead of at the top of the loop) ?  Does this mean you
>have grounded the coax braid on one side but left the other side floating ?
>Does this casue any noticeable inbalance (skew) ?

   I put the break at the end opposite the feedpoint - that is,
   I ground the shield at the feedpoint, and ground just the center
   conductor at the far end.  This is easier to construct than
   putting the break in the center.  Certainly any skew in the
   pattern is less than my ability to plot bearings.  I've tested
   it with a transmitter 600m away where I can see the antenna,
   and could detect no skew.  (You would want to test it on a car
   before using it mobile - I usually don't carry large chunks
   of sheet metal with me when I'm running.)

   I also built a version where all the wires were shielded with
   a break in the middle.  I used the braid from some old coax
   cable and passed the wires through it, then used heat shrink
   tubing to insulate the break in the middle.  I then passed
   this whole assembly through the tube and grounded both ends
   of the shield.  With the semi-transparent poly tubing (which
   seems to have the right amount of stiffness), it is easy to
   see the insulator in the center of the bundle and get it
   in the center of the loop housing.  I had to use the larger
   size tubing (12mm or 1/2") to fit the larger wire bundle.

   You can build it both ways and compare the performance.

        - Dale WB6BYU


   BTW -  I calculated the input impedance of my cascode RF
          amplifier to be around 2k5 ohms.  I'm not sure
          how well it will work with a 50 ohm load.