Studies on water movements and sediments in Southern Lake Michigan : part 1[-3] ... / by John C. Ayers.

METHODS

Currents were determined by current drogue and by the
dynamic height method of Ayers (1956) and Ayers and Bachmann
(1957). Both these methods were used in part of the studies
at USPHS anchored buoy systems; in others drogues alone were
used.
Sma-ll citizens-band (ten-meter) radio transmitters were
developed and- used successfully for drogue drifts up to three
days. The transmitters developed (Model ERC 127T manufactured
by Electronic Research Corporation of Ann Arbor) were crystalcontrolled at separate frequencies within the citizens band
and emitted an unmodulated carrier transmission which was
rendered audible by the beat frequency oscillator of the receiver, a Hammerlund Model HQ-180 all-band receiver. In use,
the transmitters were wrapped in plastic sheet and lashed
into the radar reflectors of the drogues.
Two 10-meter yagi antennae were mounted vertically on the
yardarm of the ship' s aftermast for reception of signals from
the drogue transmitters. This antenna arrangement provided a
strong lobe of reception from ahead of the ship and a weak
lobe from aft; reception from abeam was almost nil. Under good
conditions the drogues could be heard from about 15 miles ahead.
The ship was "homed" aurally on the greatest strength of signal
until radar contact was made.
Except where specifically noted, surface drogues used in
these studies were influenced by the top 7-1/2 feet of the
water. Except off Chicago, where depth was limited, deep

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