On 12/31/2017 10:42 AM, Bob McGraw K4TAX wrote:
Yes, I've done that. However, since the radio draws a different
amount of current at 100 watts CW into a 50 ohm dummy load depending
on band, the IR drop in the DC line will be slightly different from
band to band.
Most rigs that run on DC are designed to be run at 13.8V. It's important
to realize that IMD in many rigs, including the K3, increases with power
output AND with reduced power supply voltage. K6XX is an EE at Elecraft
who works in manufacturing -- that is, taking designs from the team,
putting them into production, and preliminary testing for the FCC
approval process. Bob, a serious contester, is my neighbor, and we are
both members of the Northern California Contest Club (as is Eric Swartz).
Several years ago, Bob put together a technical talk for NCCC on IMD, to
which I contributed some on-air measurements and observations on the
contributions of audio to distortion and splatter. Bob's slides include
lab measurements documenting the increased IMD resulting from operating
at reduced power supply voltage and closer to rated output. BTW -- early
K3 firmware permitted operation to 120W; that was reduced to 110W
because IMD at the higher power level was judged excessive. The slides
for that talk are at
http://k9yc.com/K6XXAmpTalk.pdf
I've since done my own measurements showing that CW bandwidth is
considerably lower at the 30-60W levels needed to drive most power amps
than at 100W. That data is at
http://k9yc.com/P3_Spectrum_Measurements.pdf
In my own shack, a pair of K3s (for SO2R) runs from a 100Ah
float-charged LiFePO battery, so terminal voltage stays in the range of
13-13.6V keydown. About two years ago, I switched to the LiFePO battery
from a big lead acid battery, because terminal voltage under load was in
the range of 12.3 - 11.8V.
73, Jim K9YC
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