Re: Hans, Does the CQX Power Meter Respond to DC?
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Hi Alan
This is correct.?
The same processor ADC input is used for both DVM (which is connected to the battery for the battery voltage measurement), and RF Power measurement. The RF measurement input will measure DC also minus the drop on the diode D4. So the RF power measurement cannot be used at any point where there is a DC voltage. So you can't use it at the MOSFET drains.?
Furthermore, even if you arrange for a DC blocking capacitor, you still can't use the RF Power input to measure RF power at the MOSFET drains. The RF detector is a simple diode detector which measures the peak voltage then converts this using a formula, to power. The formula assumes the waveform is sinusoidal. This is only the case AFTER the Low Pass Filter, not at the MOSFET drains. At the MOSFET drains the waveform is very non-sinusoidal (contains lots of harmonics) and the RF power measurement will be higher than reality.?
The RF power measurement calculation also assumes a 50-ohm load.?
The ONLY correct way to use this RF power measurement tool is to connect it at the Low Pass Filter output, when the Low Pass Filter output is connected to a 50-ohm dummy load.?
73 Hans G0UPL
On Sat, Jan 6, 2018 at 10:42 AM, Alan G4ZFQ <alan4alan@...> wrote: Looking at the CQ schematic it seems if there is a DC voltage on pin 2 of the DVM/Power meter header then it will be passed on to the voltmeter and show a power figure.
If I am right then just a voltage, no RF on the PA drains will show a RF output?
Can someone check, connect pin 2 to a plain DC source. I do not have a CQX.
73 Alan G4ZFQ
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