Key, Keyer, And Computer-Driven Keying Interconnections - Yaesu FT-991 Operating Manual

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The FT-991 includes many features for the CW operator. These functions will be detailed in the "Operation" section
later. Besides the built-in Electronic Keyer, two key jacks are provided, one on the front and one on the rear panel, for
convenient connection to keying devices.
The Menu selections permit configuring the front panel KEY jack according to the device connected. For example, a
keyer paddle may be connected to the front panel KEY jack, and Menu item "012 KEYER TYPE" used to select paddle
input.
The KEY jack on the FT-991 utilize "Positive" keying voltage. Key-up voltage is approximately +3.3V DC, and key-
down current is approximately 4 mA. When connecting a key or other device to the KEY jack, use only a 3-contact
("stereo") 1/4" phone plug; a 2-contact plug will place a short between the ring and shaft (ground) of the plug, resulting
in a constant "key-down" condition in some circumstances.
KEY NC GND
Single key/Double-speed key
If the Keyer plug is removed from the jack while the FT-991 is in operation,
the FT-991 may be switched to the transmit mode.
Turn off the power of the FT-991 before connecting or disconnecting the Keyer.
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