[Elecraft] K3/100 and the PSU

[AD6XY]

Everyone knows it is important for the K3/100 to receive a solid DC supply.

If the supply drops significantly when high current is drawn several effects
may occur:

1 - The Transmitted signal becomes wider than it should be
2 - The power control loop is upset leading to unstable output power
3 - In severe cases the radio might shut down, or engage sulk mode.

Of course this does not apply to us, we are all experienced constructors and
never make mistakes when wiring up our shacks. Like many people I run my K3
from a 13.8V DC supply that also supplies other items, in my case XV
transverters, an LP100, an LDG ATU etc. This supply is very good (tnx BNOS,
1980s) and only varies by a few 10s of mV between no and full load.
Originally when installing my K3/10 I used the supplied DC cable via a
powerpole distribution board with an appropriate fuse. In fact this
particular board had two fuses, one 30A one at the input and one at the
output plus around 1 metre of thick cable to the supply. This worked fine. 

Later I upgraded to the 100W KPA3, and of course changed the fuse in the
distribution board. The DC voltage drop according to the K3 at 20A was over
a volt, much no doubt due to the fuses and extra connections through the
distribution board. A 1 volt drop is not a problem for the K3 but will cause
more IMDs on SSB. 

I now connect the K3 directly to the PSU with as short a DC cable as is
practical. It would be even better to use voltage sensing so the supply is
regulated at the K3 end of the cable.

Mike


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