Quote:
Originally Posted by Aurificus
S/N ratios are The Issue with any detection system.
By your standards we shouldn't, couldn't, wouldn't, detect the Rx signal from a Pi MD on a Sunny day:
say 100mV in a 5 Ohm coil = 0.002W
Combined solar EM radiations/mxm = 750 W
S/N Ratio = 2.667 x e-6 = 0.000002667
Did I just hear... a pin drop? 
I say, "Be Discriminating, Focus attention on the signals...they are not the same as the noises."
LRL - If it was Easy...everyone would be doing it! 
Cheers,
Aurificus |
Hi,
is not like that.
The PI md send a magnetic pulse... at collapse of magnetic field there's a reversed voltage spike where rx take place after say 10-15us or the like.
The absolute height of the collapsing voltage is a function of force balancing e.g. energy stored in the inductor vs joule dissipation at resistor etc including the eddy currents effect: the collapse of primary field is braked a little by the opposing magnetic field due to eddy-curent in the target.
Now...
The sun relationship is not really strict... with that happens at the MD coil.
The sun radiated energy (you said 750W) is mostly due to extremely high frequency components EM waves, such as IR, visible light and a portion of UV rays (part are filtered very well by ozone layer... if still there is!
). Visible light has frequency in the order of 10^15 Hz (under 1000 TERAHERTZ!)
The PI md runs , instead, at say 100Hz or 400Hz , so 10^2 or 4*10^2 Hz ...depends on models... brands... and design (some up to 3-4Khz). At those frequencies the sun rays don't influence much (at all).
So... even a very strong solar activity , strong sunny day, don't change much for your PI... unless you have other troubles like heath generated on a black painted control box... that could make electronics to experience some thermal drift.
But if design is good, and you haven't problems with thermal stuff your PI md will work exactly the same at night than at sunny day.
You'll not hear the pin drops... cause when the pin will hit the floor it will resonate like a diapason at an audible frequency of some Khz ... but your ears are already full of strong hi volume (amplitude) notes and drums hits by the musicists there... and you're far from the pin.
The pin you'll not hear cause the impact of noise is very great cause the pin resonance happens at audible frequency, the same audible frequency of notes from concert.
But reversing the idea... what if the concert hall is in low light and the pin will generate an enormous flash light when hit the floor instead of sound ???
Suppose you coat the pin with pure metallic magnesium powder say 1gram, then add above it a thin layer of mylar 0.05mm, then you add another coat with mercury fulminate... say 5 grams...
and a final coat , thin layer of acrylic enamel.
I'm sure that even at very hi volume of the music you'll see the pin's flashlight in the low light of the hall even from 50meters back! Or even 100meters!
The fact is... you'll see the light (signal) cause the signal frequency is very different from the sound frequencies... and then the signal can travel undisturbed all the space to you without interferences... if not someone that light a cigar.
But flash is big... do you see the exit signs in concert halls ? Usually they are green glowing stuff... not much light but you'll see them too right ?
Same stuff... hall is in low light....(few noise of same "frequency") and even if AC/DC are playing 2 minutes to midnight there... (strong "noise" BUT very different frequency) you'll always see the exit signs , right ?
That's all... your S/N at md cannot be disturbed by sunlight or UV or IR that much...and directly.
Instead you'll get lowered S/N when e.g. another , same model/frequency, PI is running near yours... or your near powerlines... the noise IS in the frequency spectrum of interest and you'll get much affected S/N.
That's why e.g. Eric Foster made many units with tunable frequency... you shift a bit the frequency then cancel the noise from e.g. some powerlines harmonic or a near to yours running detector.
But that's fairly obvious... I never heard of people triggering e.g. their PI md by light! Unless you mean switching inside home the lights and then generating low frequency noise by the switch contacts.
That seems another activity LRL-guys like...
PS: maybe it's tricky stuff for some...so I explain that... I forget to say that sound is not EM... but the interference path could be supported by e.g. electronic amplifiers , coils of speakers etc... that carry actually currents modulated at such audible frequencies. Of course, sound as compression/decompression waves in a medium (air) usually don't interact directly with an electronic device... that rely on EM signals/waves unless some microphonic effects related... like the coil that vibrates due to sound waves or vibrations... and could trigger microphonic noise at receiver like happens with outdoor antennas subject to e.g. wind.
Kind regards,
Max