[FoxHunt] Ferrite antennas, nulls, 27 MHz.

[Dale Hunt, WB6BYU]

KD7JYK wrote:
> 
> Are these good enough that I can "look" through the null and see the
> building where the source is or will I be looking at a swath of buildings a
> half block wide?  How sharp are the loops?  


    It depends how far you are from the buildings.  Most of
    my experience has been with multi-turn loops on 80m.
    I'd say with a reasonable loop I can usually get within
    5 degrees, often better.  It will depend how well you
    can detect the differences on your receiver - I don't
    have any AGC so the null is very sharp by ear.  An
    accuracy of 5.7 degrees gives 1 part in 10 for distance,
    so if you are 100 feet away from a building it should
    show you the location within 10 feet.  If you suspect
    your loop has some skew, turn the loop around and
    take another bearing, then split the difference.
    Not bad for a bent piece of wire, a trimmer capacitor,
    and a short length of coax.

    One advantage of hunting the null rather than the peak
    of the pattern is that the signal strength is
    reduced by 30dB or so, but you have to make sure that
    there is no pickup on the coax or through the case of
    the radio to blurr the null.

    This presumes that the signal is vertically polarized,
    and you aren't affected by power lines or other
    disturbances in the Force. 


     Good luck!



I found a 37.5 MHz loop in the
> shop, something used by the Military, may or may not work well at lower
> frequencies, but something to try for starters to get a feel for things.
> 
> Kurt
> 
> ----- Original Message -----
> From: "Dale Hunt, WB6BYU" <wb6byu at arrl.net>
> 
> >     I'd suggest building a mobile DF loop that feeds
> >     your rig - then you can park on the street and
> >     get a good idea where the antenna is.