User's Manual

29
SHIFT F TABLE
and then
3
for Copy
All frequencies which have been removed during SCAN will be restored, and the program will
report the number of frequencies copied. If you are using more than one partition (table) you
will have to repeat this operation for each one individually. To change the partition (from the
F TABLE
menu) select item 4 (Partition) and enter a two digit number.
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).
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 (on the tundra perhaps, or inside a shielded chamber) 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 -135dBm. As a general
principle, you can hear a signal that is 12dB below the local noise floor but the same signal must
be 6dB 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 subject to
similar constraints! Thus the first line of defense against noise is to reduce the receiver gain.
Some forms of noise are naturally "bursty", like mobile voiceband messages or satellite
transmissions. Here the best remedy is for the receiver to attempt to reject signals with
inappropriate time "signatures". This is the function of the pulse interval window. Setting the