[ARDF] ARDF in Louisiana

[Kenneth E. Harker]

http://www.kenharker.com/orienteering/2004_lake_claiborne/
http://www.wm5r.org/photos/2004_ardf_yagis/

Lake Claiborne Radio-O, October 23, 2004
----------------------------------------

Jen and I traveled to northwest Louisiana to participate in a one-day ARDF 
meet being put on by the Ark-La-Tex Orienteering Society (ALTOS.)  Although 
Jen and I have been orienteering for years, we'd never been to an ALTOS 
event before - the Shreveport area is some six or seven hours drive from 
Austin - but the prospect of an ARDF course that close to us made it worth 
the trip.  The Lake Claiborne Fall Orienteering Meet is actually a Score-O
meet, and radio-orienteering was a secondary activity.  As it turns out,
Jen and I were the only two ARDFers to show up.

Lake Claiborne State Park is near Homer, Louisiana, about 50 miles east of
Bossier-Shreveport, north of IH-20.  This is one of the hilliest parts of
Louisiana, with more elevation change than many of the maps in the Houston
area.  The mapped area at the state park was not very big, which made it more
suitable to a 90-minute score-o course than traditional-length orienteering 
courses.  The forecast for the day was 80% chance of precipitation and 
thunderstorms.  Most of the rain would come in the afternoon, but we did 
get rained on a little bit while we were on-course.  Perhaps the wet 
conditions discouraged the locals who were expected to show up.

The ARDF course was set by Wayne Hatfield KD5JJP, using transmitter boxes
built by Brandon Durden N5WLG.  Each transmitter was an HT, a Byonics PicCon 
controller, and a gel cell battery in a 30cal ammo canister.  Three of 
the HTs were Radio Shack HTX-202s, one was an Icom IC-02AT, and another an
Icom IC-02A.  All the transmitters used "rubber ducky" antennas, vertically-
oriented, and were inside big white trash bags (which served as our visual 
controls instead of traditional orienteering bags.)  Because the park was 
pretty small, the transmitters were not separated by the usual exclusion
zone requirements.  Pretty much all of them were within 750 meters of the
start, and some were within 400 meters of each other.

Wayne met us in line at registration when he noticed our tape-measure 
antennas.  Wayne told us that transmitter 4 was not working at all, 
and transmitter 2 was intermittent.  As it became evident that we would 
be the only two competitors to show up for the ARDF course, we just decided 
to start at 9:30AM and give ourselves three hours. 

I turned on my VK3YNG receiver and began walking through the parking lot.
I could only hear two transmitters from the start: 1 and 5.  Transmitter 1 
was the loudest, so off I went down the road to the southwest.  I found 
the white trash bag about 600 meters from the start, on top of a hill some 
30 meters or so off the main road into the park.  Since I could still only
hear transmitter 5, I decided to go back in the direction I thought it 
might be, based on the bearings I'd been marking on the map, passing Jen 
(still on her way to transmitter 1) on the road.  I was hoping I'd hear 
another transmitter or two when I got to that part of the park.

My bearings for transmitter 5 mostly put it somewhere along the lake 
shoreline, probably inside a particular re-entrant.  After searching the 
re-entrant for some time and getting signal strength readings as high as 
3 on my VK3YNG receiver, I heard a DTMF tone on the frequency.  Wayne had
sent the reset command on frequency in an effort to get the controllers
of the non-functional transmitters to work.  A couple of minutes later,
while none of the transmitters were on, I bumped into Jen, who had found 
transmitter 1 and was now also looking for transmitter 5 in the same 
general areas as I.  A few minutes later, transmitter 1 came on again, then 
transmitter 2, followed by a minute of silence, then transmitter 4, then 
a minute of silence.  I was so close to transmitter 5, and now it was dead!
Frustration!  It turns out that I wasn't anywhere near transmitter 5, 
however.

Jen decided to hunt for transmitter 4, I think, and not wanting to follow 
her, I decided to head in the direction of transmitter 2.  I had climbed 
back up the re-entrant to the road and was taking more bearings to 2 and 4 
when I heard another DTMF control tone on frequency.  Now, transmitters 
1, 3, and 5 were alive.  And transmitter 3 was really loud.  I got a bearing
that pointed right at the gazebo used for registration.  I went over there,
didn't see anything in the gazebo area exactly, and then explored the bush 
behind the gazebo.  When transmitter 3 came on again, the bearing was 
more in the direction of Wayne's pickup truck a little ways up the hill.
Which is where the transmitter was.  I think Wayne had carried it there 
during the previous cycle!  (Its original location was out in the woods,
of course - Wayne had brought it in to see if he could figure out what was 
wrong with it.)  Jen would also find transmitter 3 at the pickup truck.

I set out again to find transmitter 5, and started in the re-entrant I was 
in before.  Failing to find it there, I concluded that I must be hearing 
echoes and began to explore up the shoreline of the lake.  The lake shore
was oriented north-south, and the several re-entrants and streams flowing
into it were mostly east-west.  I decided to go north, as there were some
signal peaks in that direction.   I went all the way to the northern 
end of the map, and even though I kept finding signal peaks in several
conflicting directions, they had all gotten less loud (sometimes no more 
than 1 on the VK3YNG receiver display.)  Going back south to the suspect 
re-entrant, the signal peaked at 3 on my display, and going to the 
slightly shallower re-entrant to the south of that, it never peaked above 
2.  I spent the remainder of my time searching both of these re-entrants 
without success.

It turns out that transmitter 5 was located even farther south, at the far 
south end of the lake, and what I was hearing in the re-entrants were echoes 
off the ridges that ran tangentially to the source of transmission.  Jen 
found it eventually, relying more on bearings from higher elevation locations 
she had visited while searching for transmitter 4 before it went off.  I 
evidently need a lot more practice distinguishing between direct and reflected 
bearings, or at least I need practice in giving up and widening my area
of consideration earlier.  So, Jen won, finding three transmitters to my two.

Despite the technical problems with the transmitters, and getting rained on
a couple of times, it was great fun to be doing ARDF again.  We've only been 
able to do three ARDF meets in the past three years, so each one is a real
treat.  Wayne did a great job hiding the transmitters, especially tricky 
number 5.

One thing that I think Jen and I are finally getting right is our two meter
ARDF gear.  At our first meet, we used WB2HOL design tape measure yagis, 
unshielded K0OV design offset attenuators, and Kenwood TH-F6A HTs.  This 
worked OK, but we thought we could do better.  At the next meet, we had 
upgraded to VK3YNG receivers and Arrow Antenna 146-3 handheld two meter 
yagis.  The Arrow Antennas looked cool, had a nice foam handle, and had 
a rectangular aluminum boom that made mounting a plate for the receiver easy.
Unfortunately, the rigid arrow shaft elements did not hold up well in the 
woods, the handle was not near the balance point of the boom, and the antenna 
pattern (optimized for forward gain, instead of for a single sharp null) 
was terrible for ARDF, with several nulls.

This year, we rebuilt the tape measure yagis.  I reused the PVC in my old
tape measure yagi, added 5" to the rear of the boom, and used PVC pipe 
hangers to mount a plexiglass plate for the receiver.  I replaced the 
elements with fresh 1" steel tape, and used RG-174 feedline instead of RG-58
(I actually have a die set for RG-174 BNCs for my crimping tool.) With 
the smaller coax, it was easy to wrap 10 or more turns around the boom 
right at the feed point to form a choke balun - this kept the pattern from 
being skewed to one side.  We wrapped the rest of the boom between the driven 
element and the reflector with tennis racquet tape (it happened to be a good
balance point as well,) and mounted another small plexiglass plate between 
the driven element and the director to which I had velcroed a baseplate 
compass.  I downloaded the reverse compass bezel overlay graphic from NZ0I's
website (http://www.qsl.net/nz0i/projects/graphics/compassrose.htm),
scaled it to the right size for my compass (300x300 pixels, as it turns out,)
and affixed it with clear packing tape (which happened to be exactly the 
correct width.)  

Jen built a new tape-measure yagi, using a modified fishing rod with a 
cork grip for the boom.  The boom-to-element brackets were quarter-round 
wood trim (which matched the curvature of the 3/4" tape measure,) notched 
and epoxied onto the fishing pole.  The steel tape was attached to the 
wood by nylon screws (and some Scotch 33+!)  She used two layers of
steel tape near the middle for reinforcement.  Her antenna also used RG-174 
for the feedline and had a current balun wound around the boom as well.
She mounted a compass plate between the driven element and the director
using more epoxy.  Because the fishing pole grip was really long, mounting 
the receiver plate at the end of the grip still left room to hold the 
antenna between the receiver and the reflector, which also happened to 
be a good balance point.  Her yagi is noticably lighter than mine.  I think
a fishing pole boom might be the best way to go - but maybe we haven't
quite found the best boom-to-element mounting solution yet.

The tape measure yagis have a really clean pattern, and the VK3YNG receiver
is definitely the way to go.

-- 
Kenneth E. Harker WM5R
kenharker at kenharker.com
http://www.kenharker.com/