Circuit Diagram

There have been many announcements about phase meters, and I have created a phase meter and amplitude meter to check and adjust the phase difference and amplitude difference between I/Q signals when I made my own PSN equipment, based on those announcements. I would like to introduce them. JA9RS has also previously published an article about this in CQ magazine, but the phase meter uses Analog Devices' AD734 (multiplier) to moderately amplify the phase difference based on a phase difference of 90 degrees, and drive a DC ammeter. The most important thing is the period from when the I/Q signal is taken in to when it is supplied to the AD734, and if a phase difference or amplitude difference occurs within the band to be measured during this period, it will cause a measurement error. The meter is a 100uA DC ammeter, and the circuit is driven by ±10V, and the meter return is set to -10V, so that 0V = center of the meter, and instead of the center meter, a normal ammeter is driven as the center meter. This meter is also a dual meter, with the black needle driven as phase/amplitude and the red needle driven as input level meter. After powering on, the AD734 takes a little time to stabilize, so it is recommended to measure after 4 to 5 minutes. The amplitude meter is an analog-to-digital AD737 (RMS to DC conversion), which converts the I/Q input signal to DC, removes the ripple component of the output with an LPF, and differentially amplifies each output with an instrument amplifier (IN101). The amplitude difference between the I/Q inputs is detected and appropriately amplified to drive the meter. The gain of both the phase meter and the amplitude meter is switched by switching the gain of the DC amplifier. The phase meter is ±1 degree/±0.1 degree at full scale, and the amplitude meter is ±1 dB/±0.1 dB. The adjustment method for both is to align them to the zero adjustment point, but this unit can also measure absolute values. However, the input amplitude is based on the condition of 3 Vpp. Zero adjustment does not have to be in the center of the meter. The position of the needle indicated by the SW=ZERO side is the target value, so you can align it to that in measurement mode. The calibration of this unit is described in detail in the circuit diagram, but both the phase and amplitude can be checked using the L-CH/R-CH output signals of the free software wave generator, however, errors will occur at frequencies up to about 200Hz (although this depends on the sound card). The 3DDS (standard signal generator) outputs I/Q signals, so it can also be used to check the calibration. �@　Input the signal to be measured from the I/Q input. Set the input amplitude so that the red needle is within the green belt near the center. �A　Set the mode switch to the ZERO side and adjust the offset. Turn the offset VR so that the black needle is in the center. �B　Set the mode switch to measurement side and adjust the object to be measured so that the black needle is in the center (the position after offset adjustment). �C　Finally, when the input signal is swung within the passband in the high sensitivity position, if it is within the green belt, then theoretically the opposite side can be kept at around 80 dB as a guideline. When you switch sensitivity or the offset changes over time, you will need to adjust the offset to the center using ZERO adjustment each time, but this is a hassle, so don't worry about it.As I have said many times, you can just make the ZERO mode position the target position.

Finished Product

Interior photo

How to adjust the AFPSN (all-pass unit)