User's Manual

Rev B
22
from your computer keyboard. HOST wakes up ready to receive data.
Now from the SRX_400 command environment press
SHIFT F0
Depending on the particular software version you are using you will either see
the Dump menu immediately or you will be given the option of selecting it. From
the Dump menu, select the Pad option. The scratchpad data will appear in HOST's
dump window on your computer screen. When all the data has been transferred,
HOST will ask you for a file name. Enter a name (up to eight characters plus an
optional extension, e.g., DATA_1.DMP ).
Example 2: Optimization
Achieving optimum performance from a radio data acquisition system entails individual
consideration of all system components and links. If you are not using Lotek transmitters, it will
be necessary to verify the optimum reception frequency of each transmitter by running the
Power Graph or Interval routines (in
SIGNAL) and varying the receiver frequency in 1 KHz steps
around the nominal value (the one supplied by the manufacturer or previously established using
another receiver). Keep transmitters and receiver reasonably well separated (at least 10 meters)
and keep the gain down to avoid saturation.
The receiving antenna is a critical system element. For maximum range and signal/noise ratio
your antenna should be tuned to your reception band, should be matched to 50 ohms (low
VSWR) and provide as much gain as possible consistent with physical size constraints. The
antenna should be mounted as high off the ground (water surface) as possible, and should be
polarized to give maximum reception for the transmitters you are using, under the actual
conditions in which you are using them (e.g., in water).
If the SRX_400 is to be operated on line to a computer or modem it is recommended that you
use a filtered RS232 cable. Special cables and connectors are available for this purpose, or a
standard cable may be coiled around a ferrite core. Contact Lotek for more information.
Finally, it is a good idea to perform some initial experiments to determine the noise floors and,
if possible, the dominant noise types in your study area(s). Although data acquisition programs
like Event_Log and Code_Log are highly adaptive in the presence of noise, some preliminary
analysis of real conditions will help you to optimize the gain reduction and noise blanking
strategies, and will provide a basis for fault diagnosis, should this ever be required. As a guide,
we have included in section II the record of an interactive session (using Event_Log version W6)
in which Event_log's noise performance was optimized for a particular set of experimental
conditions, and an experimental illustration of the function of adaptive gain control in
Event_Log and Code_Log.
Whether you are trying to locate or analyze signals, your greatest single source of problems is
likely to be noise, or more properly, the ratio of signal power to noise power in your particular
environment. Under ideal conditions you will be able to detect, by ear, pulsed signals whose
received power is less than -145dBm, and the receiver will be able to acquire and measure signals
on the order of -133dBm. As a general principle, you can hear a signal that is 12dB below the
local noise floor but the same signal must be above the noise for reliable electronic recognition.
This is the same for all receivers and as a consequence, in non-ideal environments, minimum
discernible signal levels will rise with the noise floor.
Even if the signal to noise ratio (SNR) is adequate, noise effects may still need to be
compensated. High absolute levels of noise can saturate the receiver, reducing the effective SNR,
and can prevent signal acquisition by overburdening the processor. Interestingly, the ear is