Radar and ARPA Manual

94

RADAR AND ARPA MANUAL

the setting of the gain control moves the baseline of the

noise and the threshold level toward one another.

It appears that the threshold detector

decides

whether

or not an echo is present. However it is important to

appreciate that this

decision

is based on the value of the

threshold level (which will normally have been preset

on installation) and on the setting of the gain control

selected by the observer. Ideally one would wish that, as

illustrated by Figure 2.36, the combination of these set-

tings would produce an output for all echoes and no

output for thermal noise (see Section2.5.2.3). Clearly

this is not possibl ...