[Elecraft] Upper power supply voltage limit with KX3

[Jim Brown]

Your analysis is right on target, Clay -- dissipation must certainly be 
considered. Note, however, that when he Bill suggested series diodes, he 
was specifically addressing the KX3, not a 100W K3. As to the use of 
diodes to reduce the voltage -- I'd look first at the possibility of 
adjusting the output voltage of the power supply regulator. Virtually 
all of the commercial power supplies I've seen that are intended for ham 
and 2-way radio service are adjustable over a range of +/- 5-10%.  This 
is generally true of both linear and switch-mode supplies.

In your application at a repeater site, I would look very carefully at 
the voltage and current specs of the gear. Most ham gear and commercial 
2-way gear is designed for automotive operation with an alternator 
running. 13.8VDC is the assumed nominal voltage, with possible peaks 
above that depending on voltage regulation. When used in fixed 
installations, 13.8VDC is the usual operating voltage. I suspect that is 
at least part of the basis for Elecraft's design and the 15VDC max spec.

Note also that distortion in many RF power amps is strongly related to 
power supply voltage, and is reduced as the voltage is increased. This 
is certainly true of Elecraft gear.

73, Jim K9YC

But On Fri,7/8/2016 9:07 AM, Clay Autery wrote:
> That's one way to go, but note...  that while this may work great on RX,
> heat dissipation MIGHT be an issue on TX.