Total posts : 45366
I wonder why you’re having such a hard time finding 3″ PVC pipe. It’s very common. Go ahead and go to your plumbing store and ask to look in their junk bin. Further, any re-cycle center should have it (that’s where I find, at a guess, about 80% of the hardware items I need).
I use a similar system, based on 4″ sewer pipe. It’s thinner walled, but bigger. Like the Manteca Magnum, it’s frequency-dedicated (1650kHz), i.e., no taps … took several hours of math-figuring for the number of winds, and 3 full afternoons of climbing up and down, moving the pipe up and down in the slotted bottom section to get peak resonance.
I use a modified version of this field strength detector circuit connected to a DMM:
… to find peak resonance.