Hello.
I found that when using the tune button, the power that is measured and
transmitted changes significantly.
For example, when adjusting the power control for 4 watts, the displayed
power can be between 3.3 and 5.6.
I measured the V ALC voltage, V PWR DAC output, and detector voltage and
found that the voltage sometimes looks like an unstable PLL loop which
oscillates.
At some point in time, the voltage stops oscillating and settles down to
some final random level. This can take from one cycle to as many as eight
or so cycles of voltage oscillating up and down.
I verified that the CW envelope looks like that shown in the keying mod
instructions and that the rising edge time looks the same.
I also found that this occurs when keying CW after tune has been done or the
power has been changed.
After using the CW key several times, the power seems consistent for the
most part.
I can adjust the power setting for 4 watts, key the transmitter and measure
4.8 watts. I then change the power setting to 5 watts and key the
transmitter.
I set the power setting back to 4 watts and key the transmitter again, but
the power now measures 3.6 watts. Sometimes I can see more power when
changing the setting back to 4 watts than what I measured when the setting
was at 5 watts.
The MAX534 (U8) is an 8-bit DAC which uses a 5V reference. Each DAC step
would therefore be around 19mV.
I found that most of the time, the amount of DAC voltage correction seen
between tune measurements was well beyond a single DAC step, so this to me
is not a DAC resolution problem.
At one point, I had adjusted the power for 1.4 watts and found some of the
following random voltage readings after many tries of performing tune.
Power DAC voltage
1.2 0.661
1.5 0.681
1.8 0.700
2.1 0.719
This indicates the real resolution of the power steps, but I saw all of
these powers and DAC voltages at the same power setting.
Can someone explain the exact power control algorithm?
How many power measurements are taken when "tuning" or keying, and how often
are the measurements made?
When is the first power measurement made after the power envelope starts?
How is averaging performed?
How is the amount of correction or number of DAC steps of correction
determined? Is this done in single DAC steps or larger steps?
Thanks
Jim
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