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DB9 Coupler (Male to Female)

CPL-DB9-MF

Joins two DB9 cables together, or changes the gender of a connector.

Type: Adapter
Connectors: DB9-F / DB9-M

In-depth technical details

DB9/RS-232 has 9 pins, but a basic connection only needs 3: pin 2 = RXD (receive), pin 3 = TXD (transmit), pin 5 = GND. The remaining pins carry modem-control signaling most simple serial links don't use.

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End A

DB9 (RS-232) (Female)

01 9 pins A 9-pin serial port, but a basic connection only needs 3: pin 2 = RXD (receive), pin 3 = TXD (transmit), pin 5 = GND. The remaining pins carry modem-control handshaking most simple serial links don't use.
02 D-shaped shell The D profile only fits one way round, so the plug cannot be inserted upside-down and bend its pins.
03 Thumbscrews Hand-tightened to hold the plug home. A loose one is why a picture flickers, or loses one colour channel.
04 Strain-relief boot Stops the wires flexing where they leave the plug — the exact point most cables fail.
05 Outer jacket The outer sheath protecting the conductors inside from abrasion and moisture.

Technical illustration, not a photo of the actual product

End B

DB9 (RS-232) (Male)

01 9 pins A 9-pin serial port, but a basic connection only needs 3: pin 2 = RXD (receive), pin 3 = TXD (transmit), pin 5 = GND. The remaining pins carry modem-control handshaking most simple serial links don't use.
02 D-shaped shell The D profile only fits one way round, so the plug cannot be inserted upside-down and bend its pins.
03 Thumbscrews Hand-tightened to hold the plug home. A loose one is why a picture flickers, or loses one colour channel.
04 Strain-relief boot Stops the wires flexing where they leave the plug — the exact point most cables fail.
05 Outer jacket The outer sheath protecting the conductors inside from abrasion and moisture.

Technical illustration, not a photo of the actual product

From the published standard

How it works

An inline coupler joins two cables of the same type to extend a run, or changes connector gender so two devices with the same plug type can meet. It is purely passive and neither boosts nor cleans the signal, so every extra coupler on a run adds a contact point that can degrade over time — a single cable of the right length is preferable whenever that is practical.

Function: Passive join or gender change — no signal boost
Trade-off: Each coupler adds a contact point that can degrade over time

This information comes from published sources about this type of product, not from the supplier.

en.wikipedia.org

Technical specifications

Type	Adapter
Connectors	DB9-F / DB9-M

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