Transducer Interface

Overview

The Transducer Interface attaches the acoustic communications transducer.

Connector revision

OEM modems manufactured before mid-2025 use a 6-pin connector. Newer units use a 3-pin terminal-block connector. Both versions are documented below; the analog board connector locations figure shows the newer 3-pin version.

3-Pin Interface — Mid-2025 and Later

All signal directions are relative to the OEM modem.

3-Pin Transducer Interface schematic connections.

3-Pin Transducer Interface Electrical Pinout

Pin Number	I/O	Pin Name	Notes
1	O	TRANSDUCER_OUT_P	Transducer output
2	P/I	GND/TRANSDUCER2	Board ground or second transducer input
3	P	GND	Board ground

• Connect the transducer between pins 1 and 3, with the shield, if present, connected to pin 2.
• For a second receive-only transducer, contact info@popotomodem.com. By default, pin 2 is identical to pin 3 and connected to board ground.

Hardware Components

The 3-pin interface uses a Same Sky terminal-block plug, P/N TBP01P1-508-03BE, or equivalent. Its screw-cage clamps accept the transducer wires directly.

3-Pin Transducer Interface User-Side Connector.

3-Pin Transducer Interface Components and Part Numbers

Part Number	Manufacturer	Description
TBP01P1-508-03BE	Same Sky	3-position terminal-block plug, 5.08 mm pitch

6-Pin Interface — Mid-2025 and Earlier

6-Pin Transducer Interface Electrical Pinout

Pin Number	I/O	Pin Name	Notes
1	O	TR_OUT	TR node
2	O	TRANSDUCER_OUT_P	Transducer output
3	O	AMP_OUT	Internal amplifier node
4	P/I	GND/TRANSDUCER2	Board ground or second transducer input
5	O	AMP_OUT	Internal amplifier node
6	P	GND	Board ground

• Connect the transducer between pins 2 and 6.
• Pins 1 and 3 are normally shorted with a jumper. A series matching element may instead be inserted between them; contact Popoto Modem for details.
• A parallel matching element may be inserted between pins 5 and 4; contact Popoto Modem for details.
• For a second receive-only transducer, contact info@popotomodem.com. By default, pin 4 is identical to pin 6 and connected to board ground.

Hardware Components

The 6-pin interface uses a Molex Mini-Fit Jr. connector, P/N 0039013065, or equivalent. The recommended contacts are Molex P/N 0039000074, suitable for 18–24 AWG wire. They can be crimped with Molex hand tool 0638190901; pre-crimped leads may also be used.

6-Pin Transducer Interface User-Side Molex Connector.

Pin-number orientation

The pinout above matches the analog-board pinout but does not match the orientation shown in Molex drawing 0039013065.

6-Pin Transducer Interface Components and Part Numbers

Part Number	Manufacturer	Description
0039013065	Molex	Mini-Fit Jr. 6-position connector receptacle, 4.2 mm pitch
0039000074	Molex	Mini-Fit Jr. 18–24 AWG gold-plated sockets
0638190901	Molex	Mini-Fit Jr. hand crimp tool
2153431215	Molex	Pre-crimped Mini-Fit Jr. lead, 450 mm length

Mating Cable Notes

High-voltage transducer connection

The Transducer Interface carries high voltage during modem transmissions. Voltages of hundreds to thousands of volts peak-to-peak can be present. Maintain proper clearance between exposed metal on this interface and all other metal.

Attach or detach the interface only while power is disconnected from the OEM modem to avoid electrical damage.