At 06:31 PM 8/31/2005, Tom Rauch wrote:
><Funny you can't find evidence. It's widely reported in the
>scientific
><literature, for at least the last 100 years, and probably
>longer than that.
>
>So you say. What particular literature ties charged droplets
>to hissing or musical staic noise in receivers and how did
>they determine it?
I was referring to the mechanism of charging.
Musical notes (or, in reality, a periodic discharging) from something being
charged on a continuous basis has been noted by many researchers. This
sort of thing was actually used as a very, very fast strobe described by
Fruengel in one of the "Pulse Discharge" books. It was something like a
fraction of a picofarad capacitance, very low inductance, and charged from
a constant current HV source.
There's also the well known phenomenon of Trichel pulses: high rate (as in
sub microseconds) short pulses just before breakdown, but I don't recall if
they can be sustained. Whether Trichel pulses are "tuned" probably depends
on the Q of the electrode.
In any case, a constant current charging a capacitor with a spark gap forms
a nice relaxation oscillator. The steady impact of many small charged
particles forms a constant current source. The capacitance is essentially
constant, and determined by the geometry of the widget being charged. The
breakdown voltage is going to be relatively stable (in a 10% sense).
This is no different than the neon bulb oscillator, except at a higher
frequency.
Here's a question. Is the pitch of the musical note constant regardless of
where you are tuned within a band? That is, is the signal RF, or just AF
impulses that are broadband RF.
>If it is droplets, why do I (and many others) notice that
>the SAME mositure hitting a high antenna makes the noise
>while it doesn't make the "drop hitting the conductor" noise
>on a low antenna? People with stacks of similar antennas
>notice this all the time.
It's not the individual charged drops hitting that necessarily makes the
noise (I would think that's a more constant hiss.. the sum of many drops
per second hitting). It's the charging of the object and then periodic
bigger discharges from corona.
>My Beverages for example NEVER have precipt static even
>though bare wire. My antennas on top of towers do, while
>lower antennas are very quiet even though the same moisture
>hits them all.
The amount of charge on a particle will vary somewhat with height above the
ground. Furthermore, the relative voltage will also depend on the height:
you put some number of electrons on close to the ground, and add mechanical
energy by raising it against gravity (by the wind pushing it up) and the
stored energy has to increase (partly because C is smaller, but also V
increases). Same principal as charge transport in a Van deGraaff or
Pelletron. Spray the charge on at a low voltage and the motor's mechanical
work as the belt or chain moves up raises the voltage.
There are other mechanisms for drops falling from the sky. Suffice it to
say that the charge per drop (or snowflake) is hardly a constant. I know
someone who is in the process of building an instrument to try and measure
this (i.e. what's the charge on single particles in a cloud, smoke, salt
crystals formed from dried seawater droplets, a single virus or disease
spore, etc.). It's quite a challenge to measure picocolumbs and smaller.
>Why doesn't pitch track rate of moisture? Why doesn't the
>same moisture make the same noise level on similar antennas,
>instead of lower antennas being significantly quieter?
I would guess that you're seeing many different effects
superimposed. While the qualitative aspects of particle charging are
known, there's a lot of details that aren't. Understanding the details of
thunderstorm electrification, for instance, is a real challenge.
As a related example, the folks who build tesla coils find that they are
strong emitters of energy in the VHF range, even though their basic
resonant frequency is typically in the hundred kHz area. And it's not just
harmonics of the sawtooth envelope sinusoids that are the waveform in a
Tesla Coil. Some careful probing of operating tesla coils has revealed
that it's coming from the wires leading to the primary spark
gap. Essentially, when the gap fires, it puts a transient into a dipole
radiator that's resonant at VHF frequencies (the wires are usually a couple
feet long, at most). There's also (broader band) emissions at frequencies
related to the length of the sparks produced (They act as a distributed L
and C, a few uH and a few tens of pF, connected to a low inductance C of a
few more tens of pF). Amazing what you can do when you have high power
arbitrary waveform generators, fast digitizing oscilloscopes, and EM field
modeling codes available.
There's not a heck of a lot of scientific interest in understanding the
details of the effects you've noticed, so the literature tends to be 80+
years old, and is of the "I noticed this interesting effect" nature, along
with some rudimentary surmising of why it might be so. The analytical and
measurement techniques today could probably answer the question, if someone
were motivated enough to find out. But, not much commercial value in it,
nor does it have much scientific value, at least in terms of helping to
understand larger scale atmospheric processes. There's a limited number of
atmospheric electricity scientists in the world (probably a few dozen, at
most), and an even more limited amount of money to spend on answering
questions.
If the total world research budget for dust devil electrification were
$100K a year, I'd be surprised. And that's something that's actually of
some practical interest to those of us who have to build stuff to operate
on Mars.
>73 Tom
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