Radio Power

[adept]

For the science fair this year, I wanted to do something politically correct because THOSE are the projects that always win. (Last year, the winning project was COLD FUSION from some dorks in California. (btw, it didn't work....)) So I tried to hook up a speaker with a full bridge rectifier to capture sound waves from busy intersections. Needless to say, it sucked at getting usable power and 99% of the power was RF anyway. (from the coils in the speaker). So then I started making these radio power modules.

Now that the recap is caught up with the present, I want to introduce everyone to the problem. I have measured the power a million different ways, and they all point to an exponential power curve. It's like taking a AA battery and putting it in series with another AA battery and getting 4 AA batteries worth of power. This is WRONG, but I can't prove WHY it's wrong. I simulated the circuit in LTSpice, and after 18 hours of simulating the high frequency circuit so I could have high resolution, I got a curve as seen in this screenie. (Also, the circuit is there at the bottom! )

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So, to outline the other methods I measured it with: I charged a capacitor and used J=FV^2 to calculate the Joules produced, and divided that by the 5000s to get the watts. I got the same exponential curve with a correlation factor of .998. (sorry, quadratic... easily confused!) Also, I wired up an opamp with 1,000,000x gain and measured the voltage across a megohm resistor and simultaneusly measured the voltage. got the same curve. (R^2 = .97) I have not tried a scope yet though, because I live in a tiny town where nobody has one.

So I have only one theory: I think maybe GND is oscillating when I add them in series. I have all of the series circuits with common analog ground, but GND is not connected to the negative terminal of the modules. I think that the AC is passing straight through all of my caps and going out my rectifier's negative terminal and is oscillating. But, I don't know for certain. The simulation suggests it doesn't and all my measurements say it doesn't, but it is the one thing I can think of that it might be. I do not know a way to measure that without a scope though, and there is NOBODY here in Cruces with a scope.

Please please please help me! (I have tried using my computer as a scope through the audio ports, but it doesn't work because the frequency is too high and the voltage too low...)

Stephen Jenkins

[Zad]

I'm not totally sure what the question is...

But you are modelling a theoretically perfect voltage source (i.e. capable of producing infinite current) and driving a Cockroft-Walton multiplier with it. Yes, it would produce power proportional to the square of the voltage. Each one of those diodes will need 0.6V or so before it conducts. Possibly not what you are after when you are scavenging a few mV.

[adept]

Alright Zad, I have some clarifications on the question. I want to KNOW what the power I am getting is. (It is NOT exponential because of the 2nd law of thermo.) The idea behind using the voltage multiplier is that the AC should pass through the capacitors without a wasteful diode voltage drop and should hopefully switch the diodes on without as much loss. (If you want, I can show with real world measurements why I'm convinced a x8 multiplier is best. That was about 20 revisions ago! ) I am unaware of the voltage source supplying infinite current, so that may be a solution to my problem. After inserting a current limiting resistor, I should find out in about 18 hours! But I seriously doubt that is the problem because of all the real world measurements I've taken. But it still is to be seen what the result is. In the time since I posted about 4 hrs or so ago, I've placed the results of the simulated experiment into a spreadsheet. (which I most regretfully do not know how to upload and link to... If you want I'll email to anyone interested in seeing it!) On the simulation, notice that the voltage source is set to one volt. I couldn't find a nominal figure to work with when considering noise (which is what I'd like to harness. It's no fun just stealing from AM stations. I made sure my antenna length was in the IF, where there shouldn't be transmissions.) I just settled with 1V to see if I still get an exponential curve.

Here are the results of the real world measurements I took (forgive me, not enough time to use the table command, it's REALLY time consuming to use...):
# in Series         Max Voltage    Avg Current    Watts
1                          5*10^-3            1.1*10^-6         5.5*10^-9
2                          10.6*10^-3       .6*10^-6          1.2*10^-8
3                          104*10^-3        1.3*10^-6        1.4*10^-7
4                          200.1*10^-3     1.7*10^-6        3.4*10^-7

Excluding the anomolous 2nd current data point, the fit is perfectly quadratic. The regression yields:
4.97E-8x^2 - 1.36E-7X + 8.97E-8
with an R^2 of .999

This was the results from my opamp amplified current (because I can't measure uA with my meter. Dave's uA was the inspiration for my design, so I think it's pretty solid... if not, the systematic error should have canceled as I built confidence in my measurements. just something to think about...)

Then, this afternoon, I measured using dBm (thanks Dave for showing me that too!) and I got:

-44.7dBm
-44.4dBm
-39.7dBm
-36.2dBm

and converting that to milliwatts, you get an equation very similar to the last with an R^2 of .990. And to try and get rid of meter flucuations, I measured the noise. I had zero noise as I added more wire between the probes.

That's another good installment of information. I assure you that this has been MOST frustrating to me. I've spent weeks reading the Art of Electronics and watching Dave's videos, and other forms of reference trying to figure it out. I've asked numerous forums and engineers, so it's down to you guys! Thank you for responding quickly as well! I REALLY appreciate it because my deadline is March 29th.

edit:
I thought I should share my graphs, so you guys don't have to sit and look at numbers....

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From that, I plotted the return of power versus cost and determined that x8 was the best because it cost the least per measured watt.

Because OpenOffice refuses to plot TINY numbers, I can't show the spreadsheet plots as more are added in series. But they all look very similar to the screenie of the last post except the amplitude...

Double EDIT:
I stopped the simulation in the middle of the run because the pattern was clear. (BTW, I am SO glad I know about RC time constants and didn't waste my time in the uS anymore!) So here it is:

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The power was SIGNIFICANTLY reduced... but the numbers do not even begin to explain why my real measurements are what they are. I was measuring millivolts at microamps, not millivolts at picoamps. Clearly my current limiting resistor is off. Anyway though, it isn't working right still on account that my voltage is set way high on purpose, but I'm getting less out than I would expect based on real measurements. So if I DID do the simulation correctly, can anybody explain my REAL results because they don't add up and they consistently don't add up?

p.s. Sorry about the mega long post and the double edit. Plz plz plz reply!

[Rerouter]

small point, most voltage doubler designs i see have the negative leg tied to then end of your C8, and the positive on the negative terminal of your voltage source,

would post a digram, but my simulator just crashed, so currently remaking it, also i was also noticing the slightly logramatic increase of wattate as the capacitor charged, but feel that might just relate back into time constants, as for where to measure the current, perhaps give your capacitve load your charging a 10u ohm resistor infront of one of its legs and measure on that, as that is a true reference of what current is entereing it,

[adept]

I am following the classical voltage multiplier design, but will try your idea tomorrow. (It's 12:50 am here...) I don't see why that shouldn't work... And there is indeed a logarithmic rise on the capacitors because of the time constant. Only 1 milliamp is flowing because of the current limiting resistor and I didn't start the simulator late enough to avoid the ramp up at the beginning. But trial and error will fix that! (but error takes a really long time.... ) And why even put in a microohm resistor? I agree with putting capacitance on (all except having to run the simulator until it charges, which will take an ETERNITY) but the resistor has a negligible drop in power. Especially at the low currents I'm using. Wouldn't a large value like a gigohm work better because then I would know that the current is measured in nanoamps... Anyway, my brain isn't working right, and I just read over what I wrote. Hope it sorta makes sense, because I think I'm rambling. Good night!

[Rerouter]

through my own simulations, could the exponential increase possibly be from more easily overcoming the diodes voltage drop?
it seems to me as each stage is added on the greater the voltage appearing to the next one, and as such is able to more effectivly convey its energy,

[adept]

I've thought of that, but have not setup a simulation with enough of them in series to observe that. It takes longer and longer to simulate as I add more parts (duh). But yes, that is very plausible because each added circuit in series is entering into the others rectifier as well, so that might be the cause. Someone get out a differential equation and let's solve this puppy using slope fields and lots of brute force computing in LTSpice to see what the answer is! (It should look like a population problem if you are right Rerouter) Anyway, I think I'll reduce my step value, and run some really quickies to get an idea of it all!

[Rerouter]

Here is how i am used to applying voltage doublers,
http://desmond.imageshack.us/Himg684/scaled.php?server=684&filename=quadrupler.png&res=medium

it takes quite some time to wind up, about 20-60us but should simulate rather quickly,

the 10u ohm resistor is acting like the esr of the capacitor,  and the 100 ohms on the input, can be adjusted as you see fit,

only small point to raise, by slightly lowering your capacitance values, your capacitor appears to charge faster for the first half second, i tried 1n, it not only started after 3 wavelengths, but also accellerated at a higher rate,

though i have no idea how that would effect its saturation current, or how it would respond as the capacitor exceeds 1V

[adept]

After changing my circuit to match what you suggested, I got this from the sim. (Also, it didn't take that long at all because I also used your 60us suggestion instead of waiting for 1 second!)

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Thanks for showing me how to do this, but how do I interpret this result? I have a sporadic current for a while, but it settles down after about 60us. The power is still in pW, and I was expecting to have uW. That is 6 powers of 10 off from what I'm measuring. I found someone with a scope and will get to use that Monday, so I will reply with the results of that! But yeah, I'm also going to try and set up an equation from the simulations to get the expected power output of a certain number of modules in series.

[Rerouter]

you changed the diagram slightly, still i also did not see 0.5uW until 5ms in, with such a large capacitance, it seems to take a considerable amount of time to wind up to saturation,

[vk6zgo]

I'm not quite sure what you are trying to do,but it looks like you are trying to use off air power from Radio Broadcast Transmitters.

You also seem to be using voltage multipliers to increase the voltage obtained,assuming this will also increase the power.

If so,I'm sorry to have to tell you that,whatever power you have at the input to the multiplier is all you will ever have.
The losses in the voltage multipliers are such, that you will have less power at the output.
The signal levels you will pick up will,in fact not be able to turn the first diodes on!

If I have the wrong slant on this,I apologise!

[adept]

I'm not quite sure what you are trying to do,but it looks like you are trying to use off air power from Radio Broadcast Transmitters.

You also seem to be using voltage multipliers to increase the voltage obtained,assuming this will also increase the power.

If so,I'm sorry to have to tell you that,whatever power you have at the input to the multiplier is all you will ever have.
The losses in the voltage multipliers are such, that you will have less power at the output.
The signal levels you will pick up will,in fact not be able to turn the first diodes on!

If I have the wrong slant on this,I apologise!

I genuinely hope that the energy I'm collecting is not from Broadcast Stations. When I selected the antenna, I chose 1 meter because that wavelength is well below (as in too long) for most radio broadcasts. I'm convinced that the vast majority of it is NOT broadcast stations, although I have not gone into depth with the harmonics of my antenna, and some longer (and shorter) waves ARE being collected. But most of it should theoretically be coming from the 1m wavelength waves. Anything else is horribly inefficient and won't contribute significantly. I would love to try this out in a radio silenced area. (I am going to Socorro Friday night, the largest radio silenced region in the US. I'll see if I can test it there as well! )
About the power increase, I am very aware that a voltage multiplier will not increase the original signals power. But the multiplier IS greatly increasing the efficiency in capturing the original wave. The diode switches on in a particular curve. At the voltages we're talking about, the diode is FAR from being turned on. It's resistance is probably still in the megohm's. But the thing is that the resistance through the diode IS decreased when it is turned on more. When a radio diode detector captures a wave, most of the signal strength is destroyed by the diode and must be recovered with amplification and signal processing.
So, everything that you are saying makes sense to my intuition, but it doesn't match the data I have collected. All the above conclusions I've made because they DO match my data and they make sense logically. I'm looking for anyone that can provide DATA that proves I'm wrong or more data that proves I'm right. Hopefully through this community of ingenious engineers, I'll have a kickbutt project that blows everyone's socks off!
Also, I will post up the results from my scope measurements when my dad gets back from work today. He promised to measure them out at WSMR today, so we'll see more shortly!

[Rerouter]

well just as a side point, when your down in the uA to low mA range, you can get diodes rated as low as 160mV i believe, yes, its not a common item, or even through-hole, but it would allow you to ring out some more energy if you are seeing voltages above that level, which i believe can be accomplished with a high ohm resistor between the legs of the antenna, (can be quite high voltage, but piffle all current once its loaded down, which your design works off,

still hook your antenna up to your oscilloscope and see what kind of voltages it gives with a 1M load,

[adept]

Okay, I have the scope readings. The scope revealed some interesting things. Using the scope on DC coupling (on the output of my circuit) with a x10 probe and a megohm load, just for reference. I got a noisy sinusoid at 500KHz. (almost exactly.... I was expecting MHz....). Also, just remembered, it's a digital Textronix scope... I'm not sure of the model though... Okay, so, as the modules were added, the power increased accordingly. The scope shows that the power is closer to linear than exponential though. (But it still shows slight exponentiality... (new word. learn it )) But the funny thing is that it is 500KHz. I would have predicted so much higher. That is in the IF. That's good because it's not broadcast stations. My dad thought it could be coupled from the system bus of nearby 486 PCs, but that doesn't make sense because that is encased in metal and any signal produced is so weak. Also, system buses of 486's would have been 100KHz, not 500KHz. Any ideas out there on why it happens to be such a peculiar frequency?
And Rerouter, I want to ask about these special diodes. I have never heard of such a diode. I thought the forward drop was set by the quantum mechanical "turn on" necessary to saturate the Boron atoms of the N substrate with e-'s to get everything flowing... Can you please explain what is happening that makes their drop so low? I actually tested the drop of diodes in parallel, and it appeared to drop, but I thought it a quirk of Ohm's law (because the diodes were sharing the current and so the voltage drop appeared to lessen.) That would be EXTREMELY awesome if I could get some of these diodes. I do not care if they are SMD because I know how to solder SMD well. Thanks for being such a cool guy to me!

[vk6zgo]

I genuinely hope that the energy I'm collecting is not from Broadcast Stations. When I selected the antenna, I chose 1 meter because that wavelength is well below (as in too long) for most radio broadcasts.

I hope this is a typo,as a wavelength of 1 metre corresponds to a frequency of  300MHz!
AM Broadcast stations are in the range 530 kHz(566metres) to 1.6MHz(187metres).
FM Broadcast stations are in the range 88MHz (3.4m) to 108MHz (2.78m)

The formula involved is: wavelength in metres=300/frequency in MHz.

 I'm convinced that the vast majority of it is NOT broadcast stations, although I have not gone into depth with the harmonics of my antenna, and some longer (and shorter) waves ARE being collected. But most of it should theoretically be coming from the 1m wavelength waves. Anything else is horribly inefficient and won't contribute significantly.
An antenna 1m long is a resonant length on 300MHz,150MHz,& 75MHz,as well as some others!
Apart from these harmonically related frequencies,antenna resonance discriminates very poorly against signals on very different frequencies.
It is possible to receive AM Broadcast frequencies at good strength on comparatively tiny antennas.
Radio Pioneers soon found that antenna resonance was inadequate to discriminate against interfering signals,& introduced LC resonant circuits,which were far more selective.


When a radio diode detector captures a wave, most of the signal strength is destroyed by the diode and must be recovered with amplification and signal processing.
Not so! Ever heard of a "Crystal Radio"?
These devices make use of LC resonance to cause sufficient signal "magnification" to enable them to drive a pair of headphones at useable level.
"Voltage doubling" Crystal Radios were designed,but any improvement was outweighed by the greater complexity.


Germanium point-contact diodes,which were used in the later generations of "Crystal Radios" have a forward voltage drop of around 0.2 volts.


PS: sorry for the half completed posting that appeared earlier!---Dunno how  that happened!

[Rerouter]

they are called schottky diodes, they work off a similar but different principle, this one for exampe is 160mV about as low as you can get,

http://au.element14.com/vishay-general-semiconductor/mss1p3u-m3-89a/diode/dp/1863334

as for your 500Khz signal, i would not be suprised if that wasnt some switchmode plugpack in the room you where in. it would be the only thing noisy enough to stand out above most of your other signals,

as for 2 diodes in parrellel, dont do that... it never really works out, it simply turns on the diode with the lowest drop first.

[adept]

I do make no claims to be an expert! But yes, everything you said I have heard of and considered. Also, the 30MHz is supposed to be 300. I dropped a decimal somewhere, but you seem to have found it! And the generalisation that most power is lost by a diode from radio waves stands strong. You can see that what I'm getting is NOTHING and any crystal set receives nothing also. Anyway, thanks for posting up and keeping me straight man! It makes sure that I don't slip up Friday when talking to a judge.
At Rerouter now, I want to say that I thought Schottky diodes were fast response time, not low forward drop. And putting diodes in parallel is wrong for way more reasons than that. They never share with eachother, they just steal their sustenance from everyone around them, if you know what I mean. Anyway, that is one awesome diode you showed me, but due to time constraints, I won't be experimenting with them this time. But I commend you for finding such a diode and thank you for showing me something I've never seen before.

And now I've addressed my commentators....
This is my rough conclusion as it stands. It is subject to change, but this is what I'm discerning from the results I've gotten. (Also, the excessively high vocabulary is necessary to astound my PhD see's-right-through-me judges. I've been rehearsing my presentation to make it as professional as possible.) And this is especially for you vk6zgo, because you always find my misunderstandings and correct them! (j/k, in case you didn't pick up that's a joke! )

Based on the data collected from a formidable number of sources, it can be deduced that the effectiveness of the modules increases as more are added in series. Physically speaking, the power output follows a Sigmoid curve: as more are added in series, the effectiveness increases until a maximum capacity is attained, and then the efficiency reaches its limit. A possible explanation for this occurrence lies with the diode bridge rectifier. Because the rectifier is full wave, some of the energy from the adjacent module can enter into its loop. This constant flow of electrons keeps the boron in the N-substrate saturated with electrons. Diodes have an inherent “switch-on” saturation; this follows a fundamental curve unique to the diode. As the substrate is filled with more electrons, the diodes resistance becomes less. The capacity of the Sigmoid curve is the saturation voltage of the particular diodes used in the circuit.

Also, I will be measuring with the scope again tonight and will report my findings back here again!

[vk6zgo]

" You can see that what I'm getting is NOTHING and any crystal set receives nothing also."

The headphones require electrical power to operate,which they convert to mechanical vibration (mechanical power),in order to make sounds which we can hear.

All this power comes from the RF signal received at the antenna of the crystal set.
Can your device do anything like that?

[amyk]

Okay, I have the scope readings. The scope revealed some interesting things. Using the scope on DC coupling (on the output of my circuit) with a x10 probe and a megohm load, just for reference. I got a noisy sinusoid at 500KHz. (almost exactly.... I was expecting MHz....). Also, just remembered, it's a digital Textronix scope... I'm not sure of the model though... Okay, so, as the modules were added, the power increased accordingly. The scope shows that the power is closer to linear than exponential though. (But it still shows slight exponentiality... (new word. learn it )) But the funny thing is that it is 500KHz. I would have predicted so much higher. That is in the IF. That's good because it's not broadcast stations. My dad thought it could be coupled from the system bus of nearby 486 PCs, but that doesn't make sense because that is encased in metal and any signal produced is so weak. Also, system buses of 486's would have been 100KHz, not 500KHz. Any ideas out there on why it happens to be such a peculiar frequency?
And Rerouter, I want to ask about these special diodes. I have never heard of such a diode. I thought the forward drop was set by the quantum mechanical "turn on" necessary to saturate the Boron atoms of the N substrate with e-'s to get everything flowing... Can you please explain what is happening that makes their drop so low? I actually tested the drop of diodes in parallel, and it appeared to drop, but I thought it a quirk of Ohm's law (because the diodes were sharing the current and so the voltage drop appeared to lessen.) That would be EXTREMELY awesome if I could get some of these diodes. I do not care if they are SMD because I know how to solder SMD well. Thanks for being such a cool guy to me!

Computer system busses are going to be in the MHz range. I agree that 500KHz might be an SMPS, or even a CCFL inverter in a monitor.

[adept]

I have some more data that gives me a few reasons why I don't think it is a computer bus or a lamp or anything like that any more. I think it's my scope or probes. I took the scope home yesterday and tested it again. The wave had the same amplitude and frequency. There is another theory I have though. When I got home and tested the scope probes against the 5V 1.00 KHz wave that the scope has for testing, there was something up. I was using HP x10 probes on my Tektronix scope (blasphemy, I know! ) And I was measuring 200 uV, not the 500000 uV I expected. Then I switched to channel two and got no signal at all. Also, the scope has its own internal clocking to measure the time, and it should be somewhere around this and be going into a PLL. But, at work there are only some 486's and a florescent lamp in the room, but at home, we have modern computers and incandescents. (ironic shift there, huh?) So, the environment is entirely different, and the test sites are separated by huge mountains.
And vk5zgo, it's not designed to capture anything audible so I don't think it can. Though if you insist, I have an earphone for crystal sets and could try. But you most certainly cannot TUNE my circuit as it is, so I really don't think I would get anything. And also, it still is nothing because the earphone has an exceptionally high impedance. It doesn't draw much current to put out the sound it does, like a speaker would. Everything about a crystal set is designed to be run off nothing, and I'm pretty sure the diode doesn't amplify anything, it just clips out the stuff you don't want in the earphone... Thanks for the correction, as always!