[Amps] Yaesu FT-2000 "TX-INH" Spec?

Paul Christensen w9ac at arrl.net
Thu Nov 7 23:12:39 EST 2013

 Has anyone cracked this nut yet? I'm doing a mod to my Henry 2KD-4 to
> replace the open frame T-R relay with Gigavac relays. I'm using the 
> SEQ-QSK sequencer to drive the relays. I want to use the "TX-INH" 
> (transmit inhibit) line into my FT-2000 to keep it from sending power to 
> the Henry while the relays are in motion.

Like the FT-1KD and FT-1KMP, TX-INH requires a logic-low ground connection 
in order for the FT-2K to transmit.   I ran into this issue back in the 
mid-'90s when interfacing the FT-1KMP with my Alpha amps.  The worst part of 
Yaesu's band data documentation is that it does not show a N.C. connection 
between pin 8 and GND.  When the band data plug is removed from its socket, 
pin 8 is grounded.  When the plug is inserted, TX is inhibited until pin 8 
sees GND.  This configuration is used for looped handshaking between the 
amplifier and FT-2K.

Initially, I paid no attention to TX-INH.  For testing with the Alphas, I 
didn't include the two clam shells on the band data plug -- I just used the 
crescent shaped inner insert and the FT-1KMP would key the amp just fine. 
Convinced I had it wired right, I finalized my wiring, added the two metal 
shells and covered it with the plastic boot.  Put the plug back in the band 
data jack.  No transmit on the FT-1KMP.  What the...?   After a bit of 
troubleshooting, I realized that pin 8 has a N.C. to GND, but interrupted by 
the metal shell.

So, if you want handshaking between the FT-2K and the Henry amp, the new 
SEQ-QSK Board must supply a GND signal back to pin 8 of the band data 
connector when the amp is ready for RF.   Or, if you don't want to 
handshake, just jumper pin 8 to GND and be done with it.  On some rigs, 
handshaking results in some weird CW character timing.    If the sequential 
timing on the SEQ-QSK board is set up right, you should be able to forego 
handshaking.  The timing between the rig and the amp just needs to be tested 
once -- timing of the sequenced events should not change but it would be 
good to confirm by mode in case the manufacturer uses different timing 
deltas between the amp key line and start of RF when modes are changed.

The FT-2K uses a 2SD2403 as an open collector to pin 2 on the band data 
connector.  It is Vceo rated at +60v.  Be mindful of that rating although 
hopefully, the SEQ-QSK board should use a low-voltage input pulled to 

Paul, W9AC 

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