[ARDF] maps and polarization

[Dale Hunt, WB6BYU]

  Hi Pete,

     What you really need are Orienteering maps, made
  by the local Orienteering club to international
  standards.  That is where you get all of the detail
  that really makes the map useful, including how
  fast one can run through the different types of
  ground cover.  If you have a local Orienteering
  club, the first thing to do is to ask them what
  areas they have mapped.  The maps probably
  won't be free, however, as it is expensive (and
  time consuming) to make a map and keep it up to
  date.

     Lacking that you can try using a USGS topo
  map of an appropriate scale.  With a lot of the
  map software available today you can print out
  whatever portion you want in various scales.
  This doesn't have the detail of an Orienteering
  map, but it will still show contours and major
  trails/roads.  That will at least get you 
  started.  We've even used park maps that just
  show major features on occasion - not ideal,
  but better than nothing.  As you start getting
  serious, you may have to resort to making your
  own maps - we have several people on the list
  who have done this and can help you.

     Regarding polarization:  some of the Europeans
  say that vertical polarization is harder to hunt
  in a forest due to reflections (and attenuation)
  from vertical tree trunks.  Personally I find the
  biggest differece is the pattern of the antenna:
  a short yagi will have a sharper pattern when
  horizontally polarized than when vertical.  With
  a 2-element antenna such as a HB9CV or Moxon the
  vertical beamwidth is very wide - something like
  120 degrees.  This requires a sensitive detector
  to get an accurage bearing.  The same antenna is
  much sharper when used horizontally.  For example,
  I pulled up a 2-element yagi on EZNEC and it has
  a half power beamwidth of 128 degrees vertically
  polarized and 68 degrees horizontal.  For my
  standard 3-element yagi the corresponding numbers 
  are 100 degrees and 62 degrees.

     Certainly for a practice there is no problem
  using vertical polarization, but there are
  advantages to using horizontal if folks are
  getting serious.  I mounted my set of transmitters
  on wood lathe and tied flagging around the tops so 
  they look like survey stakes.  The antenna is a
  horizontal dipole made from #12 or #14 solid wire
  (bare) which uses the top of the stake as an 
  insulator.  This makes the entire unit self-
  contained:  I just bend the wires out horizontal
  and stick it into the ground.  I can carry the
  whole set of 5 in one hand, and when I pick them
  up I just bend the antenna wires down parallel to
  the stake.  The only problem with this approach
  is that the antenna is only 18" above the ground,
  but I can stick it in a bush or tree if I need
  more height.

     With the vertical whips you may want to add
  a single ground radial wire hanging down from
  the antenna jack - the transmitters by themselves
  don't provide much in the way of a ground plane.

     Good luck!

          - Dale WB6BYU



pete sias wrote:
> 
> Hello to all,
> 
> Here in Kansas we are noted for being the flatlands
> but we do have wooded and hilly areas that dot the
> landscape. Some are suitable in my area for setting up
> a training area that can introduce people to radio
> orienteering and spur interest in the sport.
> 
> With transmitters due in today from Marvin and boxes
> drilled and ready for them, I am wanting to get a test
> course set up but I need a source for topographic maps
> that fit the ARDF scale and are down loadable, i.e.
> free.
> My searches have not turned up much in the way of
> free.
> Can someone point me to a source that will allow me to
> pick the area and print out maps to use?
> 
> Second, I notice the rules  state the use of
> horizontal omni directional antennas on 2 meters. For
> ease of setting this course up for the first time I am
> using 1/4 wave vertical antennas. Is there a down side
> to this? Attenuation is more with vertical in foliage?
> 
> Tnx in advance,
> 
> Pete   NØOY