On Sat, 8 Apr 2017 13:19:53 +0100, Gareth's Downstairs Computer
wrote:

When you consider the reduction in the size of antennae when going
from dipoles et al to magnetic loops, I wonder why those
on wildlife safaris who have attached beacons to animals
use full size yagi-udas to track the animals?

Because the collar tags transmit at power levels in the low milliwatt
range. These days, the collars use energy harvesting power sources,
solar power, and supercap energy storage. Here's someone's detailed
masters thesis on the topic:
https://vtechworks.lib.vt.edu/bitstream/handle/10919/54022/Wu_Y_T_2015.pdf?sequence=1
When you're trying to track a very low power transmitter, that only
transmits a few times per day, you need all the antenna gain you can
get. The typical 3 element VHF yagis are not very directional, but
good enough to determine the general direction. When they get close,
they rely on visual sightings and not RDF.

Surely the same reduction in size should be possible
with mag loops for VHF?

VHF magnetic loops are certainly tiny but don't have much gain.

I've seen folding VHF cubical quads used along the shoreline, where
tracking distances tend to be longer than on land.

Photos:
https://www.google.com/search?q=wildlife+tracking+antennas&tbm=isch
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
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