Setting Output Power

Jerry Gardner

What is the best way to set output power for digital modes on a Flex-6000? I have used the following two methods, but an not sure which is preferred for efficiency, etc. I like to run 25 watts output on these modes, so the examples below are based on this power output level.

1. Set the RF Power slider to 25 and adjust the DAX TX Gain slider until the "peak" bar in the Level bar graph is just below 0 dB.

2. Set the RF Power slider to 100 and adjust the DAX TX Gain slider until the indicated output power is 25 watts

Al K0VM

I personally prefer to set the RF output to MAX and use the DAX  control and/or the modem program ( wsjt, etc.) to set the actual output power.  Reason: SSDR audio clipping occurs if the Level indicator exceeds 0db.

AL, K0VM

Tim - W4TME

Either way is just fine.  I use the same method that Al uses; I set my power to 100W and turn down the DAX audio input gain to achieve the output wattage for the mode I am operating.

Steve-N5AC

If you didn't know anything about the system you were using, the general recommendation would be to keep the gain slider high and set the power low so that your signal into the radio has a high SNR.  In the case of DAX, however, everything is floating point rather than fixed point.  This is kind of an esoteric detail, but in a floating point system data retains its SNR independent of scaling.  So this is like saying that 0.444 * 0.25 * 10 == 0.444 * 10 * 0.25.  In a fixed point DSP system, you would likely lose SNR if you divide and pass the bits around first -- you would be lopping off bits and losing dynamic range.

TL;DR - Tim is correct, it doesn't matter.

Michael - N5TGL

For ease of adjustment, I set the levels in the DAX panel once and forget it.  I then use the power slider to (shockingly!) adjust the power level.  For me, this is easiest as I don't have to open other panels, and the adjustment is always right at hand.  The only time I may open DAX is if I am trying to work at QRPp levels (less than 1 watt) and the power slider doesn't let me turn the wick down enough.