Recently, I use the directional coupler and log detector to measure the forward and reflected power in a ultrasound system. the block diagram is shown as follows
signal generator input signal is sine wave, the frequency is between 1.30 MHz and 1.40 MHz (1.30 MHz~1.40MHz). The log detector is used the AD8310 evaluation board.
But when I do some experiment, the same value power (measured by the Power Meter, Bird 4421) is detected, the output voltage of AD8310 is different.
Bird 4421 Power Meter measured Value
Output voltage of AD8310
So I used the oscilloscope to measure the waveform of the two signal, the result is as follows.
Signal 1 is harmonic wave in the sine wave
Signal 2 is sine wave.
two signal have different crest factor.
as I look up for the technical document, the reason is that the intercept of log detector changed with the crest factor, and recommend the rms detector.
So I have some question
1. In the my power measurement, I don't know the measurement signal's crest factor, the rms detector is more suitalbe for me? the signal may be sine wave or may have harmonic wave
2. the sigal frequency is between 1.30 MHz and 1.40 MHz (1.30 MHz~1.40MHz), the frequency is a little low, I have search the rms detector product in your website
there are two types
(1) the output voltage is linear in voltage :ADL5511
(2) the output voltage is linear in dBV: AD8362, AD8363
Could you recommend the most suitable rms detector for me?
3. If I used the rms detector to measure power, how to convet the rms voltage value to the power value?
for example, the rms voltage value of signal is 0.8V, what is the power value?
waiting for your reply