[ARDF] DF and the "Big Project

[Dale Hunt, WB6BYU]

   While we've used 80m DF with Scouts locally and they
   really enjoyed it, my impression is that for intuitive
   ease of use simply being able to point the antenna for
   maximum signal is the simplest concept to learn.  This
   would imply that VHF/UHF may be a better place to start.

   The problem, of course, is that conventional equipment
   is more expensive on VHF.  (This may be offset by the
   fact that most hams start with a 2m rig that could be
   used with an attenuator.)  One of the less expensive
   circuits that we have been using for ELT DF is a
   simple crystal set - the perfect thing for finding a
   strong AM signal, and no battery to worry about.
   The circuit naturally gives an audio indication.
   Range on my 30mW practice beacon is a couple hundred
   feet (which makes it great for sniffing in a hanger)
   but for this application with a 1 watt AM transmitter
   and a stage of audio amplification in the receiver
   I think we can get some reasonable distances.  This
   isn't perfect since the receiver bandwidth is pretty
   wide, but may meet the requirements for simplicity 
   and cost.  To reduce the antenna size we might want
   to try it on 440 (or 220) instead of 2m, in which 
   case a PCB with strip-line circuitry or printed 
   inductors would make it simple to build.  It should
   be able to fit inside the PVC pipe boom of an antenna.

   Not everyone still has a Gonset Communicator or 
   Benton Harbor Lunchbox around to transmit AM, of 
   course.  But we already have available 1 watt
   amplifiers designed to be amplitude modulated, and
   we can build one that would take, say, 100mW from 
   an HT (for frequency agility) and put out 1 watt
   of AM.  (The Hamtronics synthisized transmitters
   can be amplitude modulated fairly easily, though
   they are expensive compared to the price of a used
   IC-2AT.)

   But perhaps where we should start first is to consider
   the typcial needs of a school program and develop our
   recommended design goals, then consider what equipment
   would meet them.  Clearly we start with:

   (1)  afforable cost for transmitter + several receivers
          Shifting expense from the receivers to the
          the transmitter probably reduces overall cost.

   (2)  ease of use - simple and intuitive to learn

   (3)  suitable for the distances typical for schools.
          This is a tough one - what is a good range?
          At a minimum a couple hundred yards - enough
          to cover a typical schoolyard.  For beginners
          a half mile is probably enough - that provides
          plenty of places to hide without getting too
          far away.  (Would students be allowed to leave
          the school grounds to find it?)  The transmitter
          power can be adjusted to limit the coverage,
          but we have to consider the effect of other
          strong local signals.

   (4)  rugged, easy to fix, little maintenance required.

   Any others that we should add?

   One thing that I have found with local T-hunts is that
   even two synchronized transmitters get too confusing
   for beginners who are still trying to learn all the
   skills.  We will want the ability to use more than one
   once the students get more advanced, but we should
   start with one on continuously.

   A good method for ID would be one of the voice recorder
   chips - that would let the teacher (or the students)
   record whatever message they want and make it easy to
   store any callsign without special programming steps -
   just push the button and record.

   Hmmm...  perhaps I should add another criteria:

    (5)  easy to upgrade to standard ARDF and/or T-hunt
         equipment.


    But whatever we do, we need to get some kids of the
    target age group involved in the planning to see what
    works best for THEM.  Most of us are, umm, somewhat
    past that age by now.  It is critical that we have
    good feedback about what kids of this age feel is
    too simple, too complex or appropriately challenging,
    and make sure that our recommendations fall in the
    third grouping.

    Might be good also to look at DF from the point of
    view of what educational objectives it can accomplish.
    At UHF in particular we can demonstrate signal blockage
    and reflections in a standard classroom.  Triangulation
    can help teach geometry.  Any other thoughts from this
    perspective?

       My ha'pennyworth,

          - Dale WB6BYU


Gerald Boyd wrote:
> 
> Dale, All
> 
> I am also copying Brian N5ZGT who is one of our local ARRL officials on
> this.
> 
> I think that some type of quick starter kit should be made available from
> the ARRL that would list resources and contacts that would let instructors
> put on a DFing program. The kit should have the step by step instructions
> for putting on a DF program.
> 
> However, Key things to making this work are cheep transmitters, receivers
> and a licensed ham (from a local club or school instructor) to be the
> control operator of the transmitters.
> 
> A possible solution is something like my new micro-80 transmitters. They are
> low power and run on a 9V battery all day. They also do the ARDF cycle.
> 
> Your kit 80 meter receiver is a good possibility for the receiver.
> 
> A resource (quick start) KIT that ARRL could produce and handout to a school
> or local ham club would be a way of having a standard program that everyone
> can use. The kit could have a video DVD showing how to DF (could also
> include the 2006 USA ARDF DVD). Brian I need to show it to you some time.
> 
> If this were to occur I think Joe would be the person to work with the ARRL
> to organize and coordinate the development efforts and program content.
> 
> If us (the DF'ers develop the kit for the ARRL) so that the upfront cost to
> the ARRL is low, then the ARRL could produce the kit. That Makes ARRL look
> good (also gets ARDF on there radar scope) and helps us by getting more
> ARDF'ers. A win win for all.
> 
> My two cents worth.
> 
> Jerry