Chuck Husick: Techno-Talk, January 2004, BoatUS Magazine - current as of January 2009
Signal Processing (DSP)
Does a newly
installed piece of electronics on your boat indicate that the device
uses “Digital Signal Processing” (DSP) circuitry? Unless
you are a circuit design engineer or a ham radio operator, it is
unlikely that the DSP label will register as something worthwhile.
However, DSP can make a substantial difference in the way a device
works. Depending on the equipment you have, the performance of your
fishfinder, HF radio and radio fax receiver may already be benefiting
from DSP technology. In fact, you may already be using DSP in your
car radio or home audio system.
DSP can greatly simplify the operation of equipment by reducing,
or even eliminating, the need for manual adjustment of controls
by automatically providing optimum results. You can see the benefit
of DSP most clearly in devices that produce an image.
DSP-equipped fishfinders, for example, can deliver exceptionally
clear images of all that lies below the boat, differentiating between
fish targets, fish and sea surface turbulence, and fish and the
In a conventional fishfinder design, the performance of the sonar
transmitter and the receiver is determined by the unchanging electrical
characteristics of the various resistors, capacitors, inductors
and transistors used in the circuit.
DSP works by substituting a software controlled, special-purpose
microprocessor, the DSP chip, for a collection of conventional electronic
components in signal processing circuits. The processing of data
is determined by software, not hardware. A multitude of operating
choices are available and can be changed instantaneously to optimize
the final result.
Specific attributes of DSP technology can be clearly seen in the
Raymarine DSM 250 black-box fishfinder. In a conventional unit,
the rate at which successive pulses of sonar energy (pings) are
transmitted, the length of each pulse and the power used is adjusted
by front panel controls. In the DSM 250, all of these variables
are controlled by the unit’s software, managed by the DSP
chip. The system evaluates the result of the chosen settings and
automatically makes changes to improve the outcome — clear
visibility of fish with minimum interference from both surface and
In the DSM 250, an echo received by the sonar transducer is converted
into a series of 36-bit digital words and processed at rates as
high as 56 Mhz. Operation at these speeds allows the system to optimize
each one of the transmitted pulses of sonar energy and to make thousands
of adjustments to the receiving circuit as each successive sonar
reflection reaches the transducer. Depending on the system, more
than 200 separate adjustments may occur in a fraction of a second.
While a conventional fishfinder in the hands of a skilled operator
can perform as well, the average user will find that the automation
provided by DSP produces superior results.
Used in a radio fax receiver, DSP will produce a clear image of
a weather map, or the satellite data, where a conventional receiver
might, at best, deliver a minimally useable image.
Successful use of a radio fax often depends on the user’s
skill in precisely adjusting the receiver’s tuning and signal
filtering circuits. However, even when all adjustments are tuned
to optimum, changes in atmospheric conditions can degrade performance.
In a DSP enabled receiver such as the Furuno FAX 30, the filter
circuit performance is automatically and continually optimized to
produce the clearest possible signal. The optimization process is
extremely rapid and remains in step with even the changes in conditions.
The value of DSP can be heard in many of the newer car radio systems
where it is used to create a synthetic listening environment that
can mimic the acoustics of a concert hall or jazz club in the confines
of the vehicle. The similarity of a boat’s interior acoustics
to that of a car or van make it likely that audio entertainment
systems sold for use on boats will soon adopt DSP technology as
a way of improving the listening experience on board.
By Chuck Husick
Chuck Husick is a pilot, engineer, sailor and former president of
Chris Craft Boats.
© Copyright BoatUS Magazine 2004