[Elecraft] RX Ant Preamps and the K3 12v Accessory Jack

[Wayne Burdick]

Hi Rich,

You could control 12 V to an external RX antenna or preamp using the  
KEY OUT signal pretty easily. This signal "floats" (open, or hi-Z)  
during receive, and goes to 0 V (ground) during transmit. The timing  
is perfect for such an application, because there's a delay between  
activation of KEY OUT and actual RF output.

The KEY OUT signal would have to be buffered to create a "12 V on RX/0  
V on TX" signal capable of powering the external device. An  
alternative would be to use the signal to directly control an enable  
line on the device, if available and of the correct polarity.

73,
Wayne
N6KR


On Aug 20, 2010, at 8:58 PM, K3RWN wrote:

> I had a thought for a future feature request.  For those of us who  
> use RX
> antennas (active and/or preamp).  It would be really cool if the 12v  
> output
> on the K3 could be triggered by the PTT.  If the 12v output jack  
> could be
> set in the menus to 0v (OFF) on PTT we could power our preamps via  
> that jack
> and kill the power on TX.  The K3 already has a built in delay for  
> RF output
> to amplifiers which can be set in "ms" as needed.  Most modern  
> preamps go to
> ground when power is removed.  This would be nice but I would assume  
> that
> the 12v output is not under control of the firmware.  Just a thought  
> for
> future expansion.