[Elecraft] K3 - Power cable voltage drop

[Don Wilhelm]

As Bob has pointed out,  power drop is not the factor in the voltage to 
an Elecraft transceiver.

No matter what the supply voltage may be, the K2/K3/K3S/KX2/KX3 will 
attempt to produce the output power requested by the power knob setting. 
  Those transceivers actually measure the output power rather than the 
drive level as is done by many other transceivers.

The problem is that the transmit IMD increases as the voltage drops, so 
running with a higher voltage results in a cleaner signal on the air.

Of course, if you are an "all knobs right" operator, you may notice a 
bit of a drop in the maximum power available on some bands.  Instead of 
114 watts, you may get only 95 or 100 watts, but that is extreme.
I recommend that you do not set the power knob above 100 watts in any 
case.  Use the maximum setting only for testing into a dummy load.

The difference between 114 watts and 100 watts is only 0.57 dB and will 
not be noticed on the far end of the transmission.

73,
Don W3FPR

On 12/28/2019 5:32 PM, Bob McGraw K4TAX wrote:
> It is not quite that simple.   Power drop is not really a factor.
> 
> The operating range of the radio, from specifications,  is 11 volts 
> minimum to 15 volts maximum.   Thus with a 4 volt operating range, a 1 
> volt drop represents a 25% change.  Within this range of 11 to 15 volts 
> the radio will attempt to deliver 100 watts by demanding the required 
> amount of current from the power supply. Thus the three resistances in 
> series example, as I stated earlier, with the middle one {radio} being a 
> variable value.