[ARDF] ARDF in Louisiana
Matthew Robbins
cedarcreek at gmail.com
Thu Oct 28 00:45:26 CDT 2004
Ken,
Regarding number 5, just a few thoughts.
With your VK3YNG receiver, the 3 should have told you it was
either pretty far away *or* not LOS to you.
For transmitters I haven't hunted before, I notice the attenuator
setting of the first one when I find it, then I move away from it and
see how the numbers drop off. I've never seen a T peak out on "3".
You said you were "in a reentrant" searching. For fairly small
reentrants, I wait on the top of the spur between the reentrants.
When it comes on, spend a few seconds finding the peak and then check
180.
One internet ARDF travel story talked about some crazy methods
Gyuri mentioned to try when you're in a high-reflection area. I asked
Gyuri about what to do if you have lots of reflections and he said
"Climb."
You should definitely try the vertical and horizontal trick,
although if the Louisiana transmitters used verticals, I have no
experience with that. With turnstile antennas, there are two things
that you should notice:
1. The sharpness of the peak. This is more for reflections off
nearby stuff. When it's hard to find the peak, it's often a
reflection. For reflections off stuff very far away, the sharpness
approaches that of a LOS signal.
2. The polarization. For turnstile antennas and LOS, when you
flip the antenna vertical, you can usually hear the whoopee tone drop
significantly. (It depends on the pitch---when you start low, it's
harder to hear it drop). Reflections tend to have nearly equal
horizontal and vertical polarization, so when you flip the antenna up,
the whoopee tone stays the same.
I find the sharpness to be a much better indicator of a reflection.
When it's a broad peak, there's something wrong. The
horizontal-vertical thing is often very subtle or even impossible to
tell (for me). I'd guess that means the signal is not truly LOS, but
that there are some objects (trees?) that mix up the polarization.
You might try to set up a turnstile w/ transmitter across an open
field, and trying to find the polarization change. Then set it up
still LOS, but with a bunch of trees in the way. I would expect that
to be more subtle than the open field.
Matthew
On Tue, 26 Oct 2004 15:32:08 -0500, Kenneth E. Harker
<kenharker at kenharker.com> wrote:
> 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/
>
> _______________________________________________
> ARDF mailing list
> ARDF at kkn.net
> http://kkn.net/mailman/listinfo/ardf
>
More information about the ARDF
mailing list