[Elecraft] Power supply for KS

[Jim Brown]

On 4/20/2020 1:05 PM, Rick Bates, NK7I wrote:
> Wayne has said that 14.2V is desirable (as read on the display, so 
> ~14.4V at the source AND the input connector at the radio).  This 
> provides a more clean signal.

That flies in the face of Ohm's law, which describes the IR voltage drop 
in the cable between the power supply terminals and the radio terminals. 
To get 14.2V at the radio, you'll need more than 14.2V at the power 
supply, and you'll need short, fat copper between them. Also, it's well 
known that most commercially available power distribution systems add 
both resistance and contact resistance to the path, so it's best to run 
a dedicated feed to the radio.

Yes, Elecraft radios have less IMD with increased power supply voltage, 
up to their maximum rated voltage.

The two K3s in my shack run from a 100Ah Bioenne Power LiFePO4 battery. 
It's much closer to one radio than the other; the power to the closer 
one is about 3 ft of #8; to the longer one, it's two runs in parallel, 
about 6 ft. I typically get about 13.4V at the radios, as indicated on 
their internal voltmeter during transmit.

Note also that IMD in Elecraft output stages is greatest at maximum 
power out, and falls by a lot at 1/4 to 1/2 power. I mostly run my K3s 
with a power amp; one feeds a KPA1500, which requires 30-40W drive for 
full output, the other an 87A, which needs 40-55W. When I want to run 
100W for contesting, I throttle the power back to a few watts and use 
the amps. The same issue is present with the 15W stage -- IMD is 
greatest just before the 100W power amp kicks in, around 15W.

73, Jim K9YC