[ARDF] Re: Protractors, 80m accuracy

[Matthew Robbins]

Charles,

    I'm confident that the error is not related to my operation of the
radio.  I'm planning to set up the situation where I think this occurs
to see if I can make it happen, and to see if moving helps.


Looking at my Brno 80m bearings:
Initial:
1: 3 degL at 2km, about 100m off.
2: 27 degL at 900m, about 400m off.
3: 5 degR at 1.6km, about 250m off.
4: 17 degL at 2.5km, about 700m off.
5: 24 degL at 2.7km, about 1000m off.

2 and 5 were the two really bad ones, both in the same direction.
2 was the strongest of all five.  4 and 5 were very weak.  5 the
weakest.  When I was over 3km from 5, I had trouble hearing it.

Later bearings:
2: 3 deg L at 1.5km, 100m off.
3: 7 degreesR at 800m, <100m off.
4: 17 degreesL at 1.1km, about 300m off.
5: 20deg L at 2.7km,  800m off
5: dead on at 2.3km, 0m off (5 minutes after the previous)

What I noticed in the Park O was that sometimes, especially around
walls and buildings and fences, the null goes away and the signal has
a very broad peak and null.  My theory is that this is some form of
multipath, and I noticed it because it was so pronounced.  I'm going
to test to see if I can show error in bearings someplaces but not
others.

More about bearings:

I currently do what Jay Hennigan has described.  I draw initial
bearings, with either numbers or ticks ( like //// across the line for
4).  When I draw in a cross bearing, I just put a small line across
the initial line.

That's what has caused me trouble.  I clutter up my map with initial
bearings, and that places too much emphasis on those bearings
visually.  I heard that Gyuri recommends drawing in the stronger
bearings, but not the weaker ones.  Anyway, the cross ticks usually
are much more accurate, but that line on the page with just the little
tick means you see the line much more than the tick.

One thing I've been meaning to try is to just draw the bearing line
for about one inch from my current location, with a transmitter
number.  That way you can scan the page for ticks toward 3, for
example, and eyeball it that way.  I think Dick Arnett does this, and
I've been meaning to ask him if he likes it.

My experience (which is limited) says bearings are much more important
for 80m than for 2m.  Or perhaps, the 80m bearings are much more
trustworthy than 2m bearings.

One thing I am certain about is the need to more-or-less continuously
check that the "other" Ts are where they should be based on your
earlier bearings.  Say I'm going to 1 for my first T, and it's a 2km
leg.  For a few seconds each minute, I verify that 2, 3, 4, and 5 are
where they ought to be.  I have found this to be essential to ARDF. 
Sometimes I just check that it's, say, northwest of me, but I check
it.  If I notice anything weird, I take a bearing and plot it.

On 2m, I've been thinking that the reason to take bearings (other than
to get the order) is so you can look for obvious reflectors and try to
pick a good place to go for your next bearing, say to try to pick
which hill to climb or which side of a a stream to go to.  I spend a
lot of time looking for good high places to go to, and if I need to
descend a significant hill, I try to make sure I won't be climbing
back up later to get one I missed.  Sometimes that means going
out-of-your-way to get a good high bearing.

80m seems much more elegant to me, while 2m is much more brute force:
Climb Hill, whoops!, Climb Hill 2, success!  In Brno 2m Day 2, I
climbed four medium-sized hills to get number 1.  170m climb.

Here's what happened:  L-R dilemma.  Pick L.  Climb 50m.  First good,
high bearing on 1.  (Major screw up 1: descend without clearing
hilltop), (Major screw up 2: get distracted, ignore good, high bearing
and chase reflections.)  L-R dilemma, pick N, climb 50m, whoops, go
back down, climb S 35m, not far enough, continue S, descend and climb
next hill 35m. success.

What I should have done:  L-R dilemma, PIck L, Climb 50m  First good,
high bearing on 1.  Realize I'm standing on the edge of the hill,
decide to check this hill first.  Go S 1000m to hill top (mostly on
trails), realize along the way that four is in front of me.  Along the
way to four, continue to take bearings to 1 (which would be mostly
clear LOS bearings).  Getting to four adds 30 or 35 m climb. Total so
far 85m.  Navigate to 1, adds 45m climb. Total after 4 and 1, 130m
climb.

Matthew
Cincinnati, Ohio USA

On Wed, 27 Oct 2004 09:07:46 -0400 (GMT-04:00), Charles E. Scharlau
<cscharlau at earthlink.net> wrote:
> Matthew Robbins:
> I walked at the 80m Park O in Brno, and I know for
> certain that 80m gets weird sometimes.  I was surprised.
> ===
> 
> I've found that 80m bearings are severely affected by nearby power lines, and other long stretches of overhead wires. Don't trust any bearings you take while standing near wires. I haven't noticed that chainlink fences, or barbed wire fences, have the same effect on 80m bearings, but I can't rule them out as sources of weirdness, so I avoid them too, on both bands. I've wondered if underground conductors (pipes and wires), especially in dry soil conditions where the ground wave can more easily penetrate the surface, can also be problematic on 80m.
> 
> If you find that movement actually helps your 80m bearings, I'd suggest taking a careful look inside your receiver. Perhaps you have a loose connection.
> 
> Sam Smith wrote:
> I just think that taking a vague direction (from your ARDF receiver)
> from a vague location (Do you really know where you are?) and plotting
> a perfect bearing on the map (How accurate is that map anyway?) is a
> waste of time. It's the old significant digit problem.
> ===
> 
> I think that one's skill level determines which source of error is most significant. For hams coming to this sport, the error in their location is likely to dominate. For orienteers coming to this sport, the uncertainty in bearings is more likely to dominate. For the WC medal winners in this sport, major errors are most likely to be caused by nervous mistakes, equipment malfunctions, and strange RF propagation effects (especially on 2M).
> 
> I agree that removing 10 degrees of error from a bearing line when the bearing measurement is only accurate to within +/- 40 degrees isn't going to help much. But when one's skills improve to the level where trusted bearings (those taken under good receiving conditions) are typically within +/- 20 degrees, an additional 10 degrees of error can significantly affect performance, especially for bearings taken far from the transmitter.
> 
> For most of Team USA, I think it's the little things we can do to eliminate silly mistakes, and time spent standing still, that will help the most. (Note: the two work against one another.) An azimuth grid can help (a little) with both those things.
> 
> 73,
> Charles
> NZ0I
> 
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