Black Box EYN257H-FF-105 Null Modem Cable — Female-to-Female, 105 Ft

The Black Box EYN257H-FF-105 is a female-to-female null modem serial cable rated at 105 feet — a purpose-built solution for connecting two DTE devices directly without an intervening modem, eliminating the need for additional conversion hardware in point-to-point RS-232 serial deployments. If you are working with legacy industrial controllers, serial console servers, or older security and access control equipment that communicate over RS-232, this cable handles the cross-wired connection that standard straight-through cables cannot.

Overview

Null modem cables are frequently overlooked until a deployment stalls because the technician is holding a straight-through cable and two female-pinout DTE ports. The EYN257H-FF-105 solves that specific problem at 105 feet — enough run length to bridge a server room to a remote serial device without a repeater or converter. The female-to-female (FF) configuration targets equipment with male DB9 or DB25 connectors on both ends, which covers a substantial portion of legacy industrial and security hardware still in active service.

The EYN257H-FF-105 (often searched as EYN257H FF 105) is sourced factory-new with no grey-market risk — a meaningful consideration when deploying into regulated or audited environments where component provenance matters.

Key Features

• 105-foot run length: Covers most in-building serial runs — server rack to remote panel, head-end to serial console — without a signal booster. At RS-232 speeds, 105 feet is well within reliable transmission distance.
• Female-to-female (FF) null modem wiring: Eliminates the need for gender changers or null modem adapters at both ends. Fewer connection points means fewer failure surfaces in a production environment.
• Null modem cross-wiring: TX and RX lines are transposed internally, so two DTE devices communicate directly. This is not a straight-through cable — important to verify before ordering if your devices require a different wiring scheme.
• Black Box serial cable lineage: Part of the Black Box serial and connectivity line, a catalog with decades of commercial-grade serial, KVM, and network infrastructure products.

Integration and Compatibility

This cable is suited for any RS-232 serial application requiring a null modem cross-over at 105 feet with female connectors on both ends. Common deployment targets include serial cables for legacy PLC connections, serial console port management, modem elimination setups, and older access control or alarm panels with DB9/DB25 serial interfaces. Verify connector gender and wiring scheme (null modem vs. straight-through) against your specific device documentation before ordering — this is the single most common source of serial cable misorders.

For environments migrating away from RS-232 entirely, consider pairing with a serial-to-USB or serial-to-fiber converter from the same Black Box catalog to extend reach or bridge to modern infrastructure while keeping legacy device compatibility.

Frequently Asked Questions

Q: What is the connector type on the EYN257H-FF-105?

A: The EYN257H-FF-105 uses female connectors on both ends (FF designation), designed to mate with male DB9 or DB25 connectors on DTE equipment. Verify your device's connector gender before ordering.

Q: Is this a null modem cable or a straight-through cable?

A: This is a null modem cable. TX and RX lines are crossed internally, allowing two DTE devices to communicate directly without an intervening modem. It is not a straight-through cable — do not use it in applications requiring straight-through RS-232 wiring.

Q: How long is the EYN257H-FF-105?

A: The cable is 105 feet long, sufficient for most in-building serial runs between a server room and a remote serial device at standard RS-232 data rates.

Q: Can this cable be used with modern equipment?

A: It depends on whether your modern equipment includes a physical RS-232 serial port with a male DB9 or DB25 connector. Many current servers and controllers have dropped native RS-232 ports; in those cases, a serial-to-USB adapter or converter will be needed in addition to this cable.

Q: What color is the EYN257H-FF-105?

A: The cable is black.

Eden Phillips

When I spec serial cabling for legacy security or industrial deployments, the two details that cause the most field callbacks are connector gender and wiring scheme. The Black Box EYN257H-FF-105 addresses both explicitly: female-to-female null modem at 105 feet. That 105-foot run covers the overwhelming majority of in-building serial console and device-to-controller distances without a repeater in line.

Technical Highlights:

• Null modem cross-wiring: TX/RX lines are transposed inside the cable — two DTE devices talk to each other directly. Ordering a straight-through by mistake is the most common serial cable error; this designation removes that ambiguity.
• Female-to-female (FF) termination: Mates directly to male DB9/DB25 ports on both devices, eliminating gender-changer adapters that add another mechanical failure point in a long cable run.
• 105-foot length: Within reliable RS-232 signal integrity limits for the baud rates typical of legacy security panels and industrial controllers, meaning no signal conditioning hardware is required at this distance.

Deployment Considerations:

• Confirm both devices present male DB9 or DB25 serial ports before ordering — female-to-female cables are correct for male-port DTE devices but wrong for anything with female ports on the equipment side.
• RS-232 signal integrity degrades with baud rate at longer distances; at 105 feet, keep baud rates at or below 9600 bps if signal quality is marginal on your run.

This cable is the right pick for server room-to-remote-panel serial console runs in facilities with legacy access control hardware, industrial PLCs, or serial-managed security appliances that have not yet migrated to IP or USB connectivity.