AIDJEX Bulletin #40 - Polar Science Center - University of Washington

etween the output of the transducer and the 10
bit counter to avoid an overload problem. With
the 10 bit counter the barometric pressure resolution
is a nominal .1 millibar.
The two temperature sensors, the spare sensors,
and the engineering data sensors are all conditioned
to provide an analog output of 0 to -5
volts. The temperature sensors cover a range of
-50°C to +lO°C with a resolution of .06OC. These
outputs are multiplexed into a 10 bit AID converter
and except for the engineering data sensors
are dumped into the memory at each three
hour sample period. The engineering data sensors
are sampled only once per day with two of the
sensors being entered into the memory each three
hour sample period. Only the 5 most significant
bits of the AID are used for the engineering data.
The engineering data presently being measured are:
RF power out and reflected power; primary and
secondary battery voltages; several temperatures
in the electronics housing and a leak detector.
The short and long term memory are operated
identically except that the long term memory is
exactly 4 times longer than the short term which
contains 7200 bits of storage. Both memories
use dynamic MOS shift register chips connected
in a serial recirculating memory configuration.
Two types of words are entered into the memory;
a sensor word which is 108 bits and a NAVSAT
word which is 192 bits. The words are entered
sequentially and once the memory is filled the
new data replaces the oldest. The word formats
are shown in Table 1. Both the sensor and
NAVSAT words start with a sync pattern. This
approach uses more memory space for non-data
and requires more transmit time than a less
frequent sync pattern approach such as once per
day. However, it has the advantage of allowing
sensor and NAVSAT words to be entered randomly
with no word limit per day. It also has the
advantage on the receiving end of improving the
amount of data received. Fading is quite prominent
on H.F. links and if a fade occurs during
a sync pattern with this scheme only one'data
word is lost where with a less frequeny sync
pattern approach a larger block would be lost.
The short term memory is normally connected to
the Bi-phase L modulator and is transmitted on
a daily basis. Once per 10 days the long term
memory is switched into the modulator and transmitted.
Two VCTCXO's are supplied to provide
redundancy or the flexibility of dual frequency
operation if needed. The present plans call for
operation on a single frequency, therefore both
VCTCXO's are the same. In the event of a failure
of the VCTCXO being used, a command can be sent
from the CCS station to switch to the alternate
one. The VCTCXO's are passively combined and
either can drive the 100 watt power amp. The
power amp is configured such that either half
can fail and still allow degraded communication
with 25 watts output. The power amp is broadband
and will provide its full output over a frequency
range of 2 to 12 MHZ. A coax switch is used to
switch the antenna from the command receiver to
the transmitter during the transmit cycle. A
matching network is used at the base of the
sleeve dipole antenna to allow adjustment for
various ice thickness. The command receiver
operates on two frequencies to allow 24 hour
command coverage. The present assignments are
4.165300 and 2.146 MHZ. The control circuits
switch the receiver between these two frequencies
on a one minute cycle. This procedure eliminates
the need for two separate receivers and is acceptable
since none of the commands require immediate
action. To assure reception of the command
on the right frequency, the CCS station merely
sends the command sequence twice with a one minute
spacing, The command is decoded and sets up
the required action in the control electronics.
Two location aid devices are provided. A 300
milliwatt VHF beacon on 108.1 MHZ allows an aircraft
to "home" on the buoy from a range of 30
to 50 miles. A strobe light allows visual sighting
of the buoy in twilight or dark conditions
with ranges up to 10 miles.
The AEB power supply consists of three banks
of primary carbon-air cells with each bank consisting
of fifteen 1000 amp hour cells. Because
of the nature of these primary batteries, they
are not capable of providing the peak current
demands of the system, therefore they are used
to charge a secondary battery bank. The secondary
battery consists of 36 Gates sealed lead
acid cells arranged in three 12 volt banks which
provide approximately 24 amp hours when fully
charged at O°C. Individual chargers are used
between the secondary battery banks and the
primary banks and the secondary banks are diode
isolated from the power buss. Thus, a failure
in any of the banks will not stiut the system
down but will reduce the life of the system.
The master timing for the AEB is derived from
a very stable oven controlled 5 MHZ oscillator.
Typical stabilities for the oscillator are 1 X
10-9 per 30 days. In 14 months there are 10,224
hours, thus the error in time at the end of the
experiment using this oscillator should be less
than 1.0 seconds assuming that the above stability
is a linear change over the 14 month life
and that the frequency was properly set initially.
AEB STRUCTURAL DESIGN
The structure of the AEB as installed in the
Arctic ice pack is shown in Figure 2. In developing
the design full advantage was taken of some
of the unique characteristics of the ice cover
sea. The ocean water below the ice remains thermally
stable with only 2OC variation and a mid
point near O°C over the entire year (4). The
ice itself acts as an insulator against the surface
temperature extremes. Equipment installed
under the surface of the ice will never see
tehperatures lower than -2OOC even though the
surface temperature may reach -5OOC (5), (6).
These facts are utilized in the design by locating
all the electronics and the batteries below
the surface of the ice in 8" diameter tubes.
The electronics modules are located in the central
tube. The temperature sensitive components
such as the master oscillator and barometers are
located in the bottom of the tube which is surrounded
by the sea water. The other electronics
modules are placed above these in order of decreasing
temperature sensitivity. The electro-
52 - IEEE OCEAN '75 17