ADDENDUM
Adjustable D.R.R. For Aqua Probe
530/540/550 Series
Digital Depth Instruments
As noted on page 9 of the Owner's Handbook supplied with your Aqua Probe Digital Depth Instrument each unit is
supplied with an advanced version of Aqua Meter's exclusive D.R.R. (Delayed Receiver Recovery) system. Its purpose
is to eliminate random false depth readings due to the presence of "subsurface interference" which consists of numerous
small particles, air bubbles, and other targets. These subsurface interference causing targets are always present in the
area just below the surface of any body of water and are capable of reflecting ultrasonic sound waves. Generally the
echos from sub-surface interference targets are considerably weaker than echos from the true bottom target. Therefore
the DRR circuit causes a reduction of the depth finder's receiver sensitivity to weaker/shallow/targets and allows the
sensitivity to recover to normal levels for deeper/stronger bottom targets at a carefully controlled rate.
The D.R.R. circuit in your Aqua Probe Digital has been factory calibrated for the optimum level of sensitivity reduction and
recovery rate. As received, the DRR in your unit will eliminate erroneous false readings due to all but the very most
severe cases of subsurface interference. However, there may be some conditions where field adjustment of the DRR
circuit will be helpful to compensate for abnormal conditions. As an example, if the bottom composition is very muddy and
silty, or if there is heavy growth of marine vegetation (seaweeds) in the area where you do most of your boating, the
bottom echo may be very weak. Such a bottom condition will absorb much of the ultrasonic sound waves, thus, requiring
additional receiver sensitivity and a slightly reduced amount of D.R.R. Or as another example, consider navigating
through
a
heavily
trafficed
channel.
In
this
area,
the
