300mV of what? I thought you were measuring some distance or something. Can you please label what each axis actually is and how it relates to the circuit?P.S. The graph shows real measures. A "300 Km." swing translates into roughly 300mV. I didn't bother to change the units, sorry.
that would negate what the OP seems to be trying to do, he's using the output amplitude to measure the proximity to an external capacitance.AFAIK, usually oscillators are tied by some non-linear impedance such as the famous H&P's light bulb, so that the amplitude relies less on power supply rails and clipping and is more predictable.
actually a chemical process such as that in a battery is a noise source. the noise is generated by the random nature of the recombination of individual ions and electrons at the battery electrodes. the voltage of this noise is lower than what you would get with a zener, but it is still there nonetheless.The real circuit shows this noise even when powered by a battery, which has the lowest noise figure of any power source.
actually a chemical process such as that in a battery is a noise source.
that would negate what the OP seems to be trying to do, he's using the output amplitude to measure the proximity to an external capacitance.
you might not be able to use it beyond a certain distance. the electromagnetic field around L1 is governed by the inverse square law, so there's going to be a finite distance from L1 where an object won't have an effect on L1.Not a capacitance, but an inductive coupling. Look at the object to be detected as the secondary of a transformer. The circuit does its job at short range very well, the problem being the high noise level that greatly reduces its usefulness at medium range and beyond.
you might not be able to use it beyond a certain distance. the electromagnetic field around L1 is governed by the inverse square law, so there's going to be a finite distance from L1 where an object won't have an effect on L1.
Correct, but I happen to hold the record at R.M.I.S.C. (Rock Mountain Information Security Conference) for correctly reading a passive RFID tag at a distance of 25 feet. You just have to know where to look in the noise floor. Over sampling techniques are a way to increase the signal to noise ratio by a process known as Ensemble averaging. Basically your SN ratio is equal to the square root of the number of samples you acquire.the electromagnetic field around L1 is governed by the inverse square law, so there's going to be a finite distance from L1 where an object won't have an effect on L1
Would someone be kind enough to post an actual schematic please?
L1 and C2 are essentially tuned to about 577kHz ... There is plenty of noise there. What your circuit may be doing is something of an Active Antenna effect. Even though your driving the LC you wouldn't think it can act as a receiver, but that's exactly what some Active Antenna's do. Any wires leading into or out of the LC will exaggerate the effect.
Believe it or not, in your oscillator circuit I see a path that could act like a decent receiver..... I use a similar one transistor version in some of my receiver designs. What you have effectively is a symmetry of my receiver on each rail. See attachment for similarities, I believe the Base follower receiver is what you essentially have.
I can see a couple of problems with the circuit.
1. By subtracting a fixed 37 volts, the relative noise voltage increases significantly. If the noise voltage is x then x/3 is much greater than x/40.
2. Using a current source and a resistor as a means to subtract the fixed voltage is a potential noise source. Have you considered using a 37V zener? Yes, zeners are noisy too, but it would be interesting to see a comparison.
What you are doing strikes me as a strange way to detect the effect of nearby metal. There are a number of proven methods.
Over sampling techniques are a way to increase the signal to noise ratio by a process known as Ensemble averaging. Basically your SN ratio is equal to the square root of the number of samples you acquire.
Correct, but I happen to hold the record at R.M.I.S.C. (Rock Mountain Information Security Conference) for correctly reading a passive RFID tag at a distance of 25 feet. You just have to know where to look in the noise floor. Over sampling techniques are a way to increase the signal to noise ratio by a process known as Ensemble averaging. Basically your SN ratio is equal to the square root of the number of samples you acquire.
All that aside, I suspect much of the "noise" is simply from external RF interference making its way into the coil.
Perhaps I missed it, but I was not able to find a schematic that the OP is using. That might help my assessment of what might be going on.
EDIT: Ahh I see... it's in a SPICE file. Would someone be kind enough to post an actual schematic please?
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