You don't NEED anything like an RF RMS voltmeter. or phase detector. A
diode probe on a VTVM or very minimal scope will do just fine. You tune
for the typical 'rabbit ears' [flat phase] response.
Phase MIGHT be important in a wide band microwave communication system
using BPSK or QPSK or NPSK, but not in audio gear.
Hmm, I've been tuning a lot of 2nd order 500Hz low pass Bessel filters and the
most accurate way of tuning them was to tune for proper phase at cutoff
frequency. IIRC it was supposed to be 45 debgrees. Frankly said, I don't
quite know how else I'd go about tuning them anywhere near same accuracy -
you can detect small phase changes very well, while detecting the peak of
amplitude response *to the same accuracy* is kinda hard.
I've seen a similar thing in narrow bandpass filters: the peak of the response
is where your amplitude envelope slope is zero, so by minimally tweaking the
tuning you get close to zero change in amplitude. So the only way I found to
do such tuning with good accuracy was to look at phase. But then I didn't
really have much RF experience, so I may be talking complete BS. I'm only
relating what has worked for me.
Cheers, Kuba
