The QRP Homebuilder webpage gives a full description of the use of the calibrator. Interestingly this is a square wave generator which I understand results in a better more accurate result than a sine wave. I assume that this is due to the huge bandwidth (500Mhz) of the AD8307. Thus a square wave will generate harmonic energy all the way upto 500Mhz which is 'captured' by the AD8307 and summed to a power number. The generator is calibrated to a 50mV DC source and was easily done.
Note that this calibrator cannot be used with attenuators to calibrate any other power level than the -10dBm level. For that task a sine wave generator must be used (makes sense).
At this point I changed the input resistor on the Power meter to a 1% tolerance 52.3Ohm unit from the original 51Ohm unit. Interestingly the measured -10dB point only changed from 1527mV to 1527.3mV.
The wave form below is not exactly a squarewave reflecting the limited 20MHz bandwidth of the scope.
|ZS6RSH Build of the CMOS 10MHz calibrator|