[AMRadio] A question about a National NC 2-40D receiver

JAMES HANLON knjhanlon at msn.com
Fri Nov 8 14:41:55 EST 2013

The NC-240D was designed to be muted by an attaching an external relay to the BSW terminals on the back.  The BSW (B+ SWitch) terminals are in parallel with the B+ switch section of the POWER SUPPLY rotary switch located beside the S-Meter.  If you leave this switch in the B+ OFF position, you can turn the receiver off (mute it) by opening the connection across the BSW terminals, and of course return the receiver to operation by closing the connection across the BSW terminals.  
In case you want to operate CW and to use the NC 2-40D to monitor your transmitter, you can use a SPDT relay with the swinger attached to receiver chassis ground.  Break the lead on the RF Gain control that goes to ground and put a 10K or so pot in between the RF Gain Control connection and ground.  Attach the junction between this "CW transmit volume" control and the RF Gain control to the relay contact that is grounded when the relay is in its "receive" position.  Attach the other relay contact to the antenna input terminal.  In the "receive" position, the relay attaches the bottom of the RF Gain control to ground and the receiver operates normally.  In the "transmit" position, the short across the "CW transmit volume" control opens and a short-to-ground is placed across the antenna input terminals.  You then adjust the "CW transmit volume" control for appropriate volume while sending.  
Enjoy your 2-40.  It's a great receiver.
Jim, W8KGI

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