The Sperry Marine P/N 03956-1982770 is the specific Electronics Unit (Main Processor) for the SRD-500 Dual Axis Doppler Speed Log.

While the bridge display shows you the speed, this panel is the “brain” typically mounted in a rack or on a bulkhead in the electronics room or bridge console interior.

Panel Internal Components

If you open the 03956-1982770 enclosure, you will find several key sub-components that are often listed on the internal product tags:

• Main PCA (Processor Board): P/N 03956-1982772. This is the primary circuit board that handles the Doppler signal processing.

• Power Supply: Typically a Condor GPC140-12 (or equivalent 12V/24V DC switching power supply) mounted directly to the aluminum base plate.

• Interface Terminals: A series of terminal blocks where the transducer cables and NMEA 0183 output wires are landed.

Panel Functionality

The 03956-1982770 panel performs three critical roles:

1. Excitation: It sends the high-frequency electrical pulses to the hull transducer to create the 307 kHz acoustic pings.

2. Calculation: It receives the return echoes and calculates the frequency shift to determine longitudinal (fore/aft) and transverse (port/starboard) speeds.

3. Distribution: It converts that raw speed data into NMEA 0183 sentences (like $VDVBW and $VDVHW) and sends them to your Thrane & Thrane 403616B interconnection box for GMDSS/SSAS reporting.