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Jeremy Malczyk [[log in to unmask]] writes:

>>100 meter range in and of itself is not very useful- field strength
>>changes of a few meters are swamped by the change in magnitude change
of
>>a few degrees of angle at that distance- can spend a lot of time and
>>energy figuring out which is the correct direction to move.
>
>True, but from the cursory look I took at the Pieps, that 100 meter
range
>included digital distance readings (not sure about direction), which
would
>take some guesswork out of long range searching..

The distance is a highly inaccurate function on any of 'em, relying on
presumptions about emitted power on the buried transmitter end, and
orientation & shape of the antenna(e) both at the transmitter and the
receiver, etc. etc. Don't count on it's accuracy being within 50% of
reality ever, no matter how many digits are displayed! And the direction
is not possible to determine without much larger antennae, or arrays
much much bigger than would fit in your pocket.

>Also, I was under the impression that after a certain distance the
>effective shape of a transmitting beacon's field becomes more or less
>spherical.

It does, a couple of miles out.  A single wavelength of 457kHz is about
650 meters. At about 10 wavelengths (6.5km) it's isotropic enough
though... so at 6.5km out you can pretty much go straight in for quite
awhile, if you can tell which is the right direction along the axis! :-)

>If that's the case, a beacon that can pick up signals 100 meters away
may
>not have to rely on a flux line path until you get closer in (meaning
you
>take a more direct path further out, then spiral in for the last 40-50
>meters).

Which is my point exactly- you _must_ assume a near-field phenomenon,
and assume that it's a possibly distorted, near-field magnetic dipole.
If you don't your mental-model of what's going on is way, way, off and
will lead to false assumptions.  Better to think of it as DC, the
iron-filings on the paper with the bar magnet under it than an isotropic
spherical RF field. Flux line searches are "straight enough", and much
more direct than grid searching.

I suspect the 3 antenna array makes it easier to correct for axis
errors, but I can't imagine how 3 tiny ferrite core antennae in a pocket
sized box is gonna get you enough info to tell which direction along the
axis the transmitter is.

> I guess I should test it. They have one in stock right across the
street.

Do! I'd love to hear the details, particularly the learning-curve (some
digital interfaces _suck_!!)

dana

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