Spent several hours building cables for the NCS-3240 and finally got it wired into the shack this week.

This unit allows the selection of four transmit audio sources (such as microphones, SSTV gear, TNCs, what have you) and four radios. It also routes keyer output to the selected radio, and RX audio (if used) from each main (and sub) receiver to a left and right speaker. My operating position where the -3240 is used features an FT-980, FT-102 and two FT-726Rs. A DTMF hand mic, MD-1 desk mic and a Kantronics KAM are the audio sources. The -3240's rear-panel Aux1 and Aux2 audio connectors were used to interface the TNC to the rigs. Speaker or Line-level Receive Audio can be routed by cable construction and input device selection...but in a nutshell, my setup has either of the two HF rig's Line Out signals connected to the KAM's HF Radio port when they're selected. Likewise, the FT-726Rs are connected to the VHF Radio port upon selection of either radio.

A couple of gotchas for future reference in case anyone else happening across this thread has the units and is puzzled about the way they operate:

  • ALL PTT lines are active at any one time, not just the selected source. Careful about bumping the mics or leaving the unit unattended if the selected transceiver is in a carrier generating mode as the rig will be keyed inadvertently.
  • If using the rear-panel PTT connection to mute a companion NCS-3230, a couple of 1N4148s or similar may (or may not) be needed in the line to prevent the -3240 from muting the -3230 when the unit isn't in TX mode. These are wired in series with the cathode end of the string to the -3240's PTT connector center pin, and the anode to the -3230's Mute All connector: 3240 (PTT) ---|<|---|<|--- 3230 (MUTE)
  • When using the -3240 with a TNC or other device which momentarily activates its PTT line upon power-up, make sure the -3240 is off -or- no radios are selected when you turn the TNC or other device on. If not, you'll briefly place the selected radio into Transmit.


All in all, a great combo. I wish they were still manufactured.

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