FW: FW: FW: [Elecraft] power control (was kit arrived)

[Don Wilhelm]

Brett,

The power output is totally controlled by the microprocessor.
The power knob (think of it as 'power requested') setting is known to 
the microprocessor (full stop of thought here).

When the transmitter is tuned or keyed, the output is measured by the RF 
  detector (or wattmeter if either the KPA100, KAT2 or KAT100 are 
installed).  That power output level is scaled and sent back to the 
microprocessor on the VRFDET line.  The microprocesor then compares the 
actual power output with the requested power and changes the VPWR from 
control board U8 as a response.  The VPWR signal is fed through the 
keying waveshape and ALC ciruit (Control board U10A and Q8) which 
produces the VALC voltage which is then fed to the drain of RF Board Q24 
to control the amount of BFO injection into the Transmit Mixer.

The /BANK1 signals on the front panel are the scanning lines that tell 
the microprocessor what the state of the buttons and controls are - 
there is no direct control done on the front panel (except that the RF 
Gain and AF Gain controls are fully analog and not microprocessor 
controlled).

73,
Don W3FPR

Brett gazdzinski wrote:
> Can anyone describe how the power output control actually works?
> I traced the circuit to the bank 1 part, I have no idea what bank 1 is.
> 
> The cpu seems to have some control over the power output, looking
> at the output power sense circuit to display output power
> on the bar graph and as a digital readout when in the tune mode.
> 
> You adjust the power control, but what is that actually doing,
> changing the drive level to the PA by way of Q10, or something else?
> 
> Brett
> N2DTS