On 7/2/19 11:47 PM, Hal Murray wrote:
jim...@earthlink.net said:
Actually, it's because someone asked me about a science experiment where
you'd place them in a neighborhood outdoors.
Sounds like another science experiment: build an antenna to pick up 60 Hz.
You could start with the typical ferrite, coil, and cap. Just adjust the cap
to your new target frequency. Simple to try.
I ran through some quick calculations on that - unlike for AM band, you
need a fairly good sized capacitor. I think it's doable. A typical
loopstick for AM is around 0.5 to 1 mH, so you'd need about 7000
microfarads to resonate it at 60Hz. So, a LOT more turns on that inductor.
And then you have to start worrying about phase shift - it's going to be
a fairly high Q resonant circuit, with the phase varying most rapidly
around resonance.
So a resonant antenna probably isn't the way to go..
The whole goal is to look for phase shifts after all.
That's why I was thinking about magnetic field sensors..
The little electronic compass sensors sample at 100-300 Hz and have
sensitivities comparable to the Earth's field (i.e. something like 2
Gauss, 200 microTesla, full scale).
I don't know that they're sensitive enough - I recall that typical line
frequency fields are in the "single digit milliGauss" range. If I
convert that the E field, I get "single digit Volts/meter" - which is
consistent with my tens of mV holding the scope probe in my hand.
Well... since it's a holiday weekend, it's time to break out the Beagles
and Teensys and do some experiments. It's just that I don't like E field
sensors (if for no other reason than High Z amplifiers get destroyed by
ESD)..
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