Lock In Amplifier for Expierment

Using Arduino Project Guidance
1

Hello all,

I new at all of this, so if I sound like I don't know much, well, that is correct. But I want to know more, and I would appreciate your assistance.

I've been working on a physics experiment at home that is similar to the Michelson-Morley experiment but uses radio waves instead of light. In my experiment, I am creating a standing radio wave on a Letcher Line and looking for very small changes in electrical output on the line as there is a change in vector.

I had a brief conversation with a physicist on a chance encounter and he suggested I use a lock in amplifier to look for these vary small changes in electrical output (in volts). I took a few notes and I have been trying to figure out how to do this. My career is medicine, not physics, but I really want to do this experiment.

I purchased the "Taidacent Lock-in Amplifier AD630 Module Minimum System Phase Sensitive Detection Weak Signal Conditioning Balanced Modulation" on Amazon.

Unfortunately, I don't really know what to do with it. In my experiment, I'm sending a RF signal down the Letcher line with an RF generator. I am not certain how to connect the RF generator and letcher line to the Lock in Amplifier. I am also not certain how to obtain the readings from the lock in amplifier.

As I said, I'm new at this and I'm interested in learning. It keeps my brain sharp. Any assistance would be greatly appreciated.

Rene Steinhauer

2

Where does an Arduino figure in this project ?

3

I don't know the answer to your question and this isn't the right place for it anyway, However....

I am fascinated by your experiment. As Michelson and Morley used light over a long distance, which seems highly necessary, and LIGO also uses a similar set up, also to detect tiny changes in flight time of the measurement signal, I would have thought a short wavelength and a very long path length would be per-requisites to this kind of experiment, but what do I know?

As this is not Arduino related but as there might be people here who can help then maybe 'bar sport' might be a better location for this discussion, not sure.

Bob?

4

You wrote: "I am creating a standing radio wave on a Letcher Line and looking for very small changes in electrical output on the line as there is a change in vector.". In understand the Letcher Line from reading pre-WWII books when I was a child. I under stand standing radio wave, which are the product of applied RF power and the power reflected from the end of the Letcher Line.

But I have no idea what you mean by "a change in vector". Please enlighten me.

Paul

5

“ Expierment “... I like spearmint too.

6

Hello,

I guess I missed the more important aspect of this forum. I plan to connect the lock in amplifier to the Arduino UNO board. I see someone else is doing something similar. That's why I have started on this forum. I'm certain I will need help figuring out how to do that and code as well.

The Michelson-Morley experiment used a system that looked for changes in light speed when moved into two different directions (or vector). My experiment is similar but using standing radio waves and a change in direction. It's not likely that the results will be different, but it is a new idea on how to examine the same concepts with a different experiment. I hope to publish my data in a journal, but I need data. My prior attempts were not technically sufficient to obtain reliable data.

As I mentioned previously, I'm new to this. My output will need to go to the Arduino board were I will need to obtain voltage readings. Additionally, I have thought about having my lecher line on a spinning platform (Rotational stage) that will also be connected to the Arduino for control of the rotation. I would like to graph the readings and look for a "blip" showing an change that occurs on a specific vector. To keep wires from becoming a problem on a rotating stage, I will need to connect blue tooth to transmit the data to my laptop.

Any chance this now is appropriate for this forum? I can see how my first post was not obvious about that. Sorry, my mind was wrapped around the lock in amplifier.

Any assistance is greatly appreciated.

7

Any chance this now is appropriate for this forum?

I guess it is!

I'm very interested in what you find with your experiment, please do keep us updated.

8

Remember the Michelson and Morley experiment famously found nothing. I can’t see how your experiment can possibly produce anything else. Remember if you do see something and you can can trace it to what Michelson and Morle we’re looking for then you will be proving Einstein wrong, so let’s be realistic about this. It ain’t going to happen. From a physics point of view it means that the behaviour of EM waves depend on their frequency, of which Clark Maxwell will have something to say about it.

I used to use a Letcher Line to demonstrate the the authorities my ham transmitter was in the right frequency, I don’t think hams in the UK are inspected like this any more. It was in the days before frequency meters could measure UHF.

Remember that although the standing waves are on the line, they are still going up and down at the transmitter frequency. Will your lock in amplifier cope with that sort of frequency?

To couple the signal into the amplifier use a single turn pick up coil placed at a point along the line where you get a maximum reading.

9

The classic definition of a "vector" has magnitude and direction. I guess you are using the word geographically. Need to use a different term.

Paul

Also: Look at the December 2019 and January 2020 issues of QST magazine for articles on "visualizing microwaves". Might be you can find something of interest there.

10

I used to tell my students that a vector is an action with a direction. So fuck off is a vector.

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Remember if you do see something and you can can trace it to what Michelson and Morley we're looking for then you will be proving Einstein wrong, so let's be realistic about this. It ain't going to happen.

However, in the extremely unlikely event that you do find something, and it's verified and accepted by the wider physics community then you can look forward to a Nobel prise for physics...

12

Well no not automatically, it has to be duplicated by others, that is it has to be repeatable. Then it has to be explained, what is going on here. Then it has to be worked into general relativity and proved to be useful. That will take decades, you don’t get one for any discovery of an anomaly or something new with no application. See how long it took from the discovery of laser action before a Nobel prize followed.

13

Mike, that's kind of that I meant when I said:

...it's verified and accepted by the wider physics community.

You just spelled out the details of what that means.

14

Thanks for the input. Will I prove Einstein wrong? Probably not, but it's fun to try. This experiment is a culmination of years of study (as a hobby) on the subject. It was not that the Michelson-Morley experiment did not find anything. They were looking for the aether. I'm not looking for the aether; I'm just looking to understand the physics of all of this. I suspect my results will not lead to a Nobel, however, if I can obtain reliable and reproducible data, than the work would be reasonable for publication. I would be satisfied with that.

So for those who tell me, "It's been done," I know that. But at some point, you want to see theory in practice. I can, and have, reproduced the original experiment. I want my own experiment. I'm learning so much about the process, electronics and personal patience. It's not the outcome, it's the journey.

I'm on a journey. Who wants to join me?

Rene Steinhauer

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I want my own experiment. I'm learning so much about the process, electronics and personal patience. It's not the outcome, it's the journey.

++Karma;

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I'm on a journey. Who wants to join me?

Sorry but I live at the destination.

17

Couldn't help but be curious, so had a quick skim read, in no way do I really understand the experiment, but possibly have gained a feel for some of the parameters. I've also taken note that wiser heads than mine are sceptical (as I am), but also taken note of the desire to pursue the experiment further.

I'm pretty sure a scientist/engineer would crunch some numbers on the theory/hypothesis, (and it's actual possibility!), develop a performance spec for the equipment, and then analyse error and uncertainty for each possible solution/technique to see if meeting the spec for detectability is possible.

For a start, one would think if you have a possible phenomenom to observe, you would need to calculate/estimate the expected signal level change to measure (a small change in signal amplitude caused by a minute change in arrival time on a lecher line used as part of a phase detector?), and see if it is indeed observable, extractable, and can be isolated from all other sources of system error and uncertainty, of which there are many. Including electrical, mechanical, thermal etc. Even the RF source will have variation that may need to be accounted for.

So for one example of mechanical stability, we have a vhf lecher line at work - it's made from two tightly tensioned 1/8" brass rods about 5' long, but they twang like guitar strings which would surely be a huge source of error in a system where minute changes in arrival time are trying to be detected. so such errors need to be minimised by design, and accounted for as much as possible.

The purpose of a classic lecher line is different from what I think I understand you are trying to achieve, so an immediate problem for detecting changes in arrival times with standing waves (and perhaps pulse/radar transmission techiques in stead of CW), would be how to implement the most stable transmission line possible that has an injection port and sniffing port.

That's starting to sound like a rugged microwave wave-guide with a mismatch at one end and a circulator/duplexor, downmixer/synchronous detector and your data acq at the other. Its possible this could be implemented with stripline and modern solid state/miniature devices rather than the classic microwave "piping" one automatically thinks of. I could also be completely off base :slight_smile: . , one would think if there was an observable phenomenom like you are looking for caused by rapid movement and vectoring of waveguides and/or aerial systems, it would be well-known and accounted for in radar systems.>

18

Thanks for the reply. In your first part, you mentioned,

"For a start, one would think if you have a possible phenomenon to observe, you would need to calculate/estimate the expected signal level change to measure (a small change in signal amplitude caused by a minute change in arrival time on a lecher line used as part of a phase detector?), and see if it is indeed observable, extractable, and can be isolated from all other sources of system error and uncertainty, of which there are many. Including electrical, mechanical, thermal etc. Even the RF source will have variation that may need to be accounted for"

I agree that it should be possible to know how much change will occur. I've been asking myself that question and trying to learn more about the mathematics of the Sine Wave. My career is in medicine, not in physics. As such, my math ability is simply below what is needed. I've been unable to find anyone who may be able to work out the math with me. I know the expected change will be very small, and I am concerned that if there is a difference, it may be too small to be obtained with my equipment. Regardless, I want to do the experiment and figure out the mechanics of it all.

As for the lecher line. It does not have to be high tension or moving. I've made them with parallel thick copper wire and with copper tubing. Fortunately, it is simple enough to determine if the system is working by taking simple measurements along the line.

Step 1, for me is getting the Arduino Uno to manage the rotation of the stage. I have parts arriving today, and I will get started on it tonight. Wish me luck.

Rene Steinhauer

19

I agree that it should be possible to know how much change will occur.

Therein lies a problem: I can tell you how much change to expect with no maths whatever; Exactly the same amount as the damage the bulldozer would have suffered if Mr. Prosser had allowed it to roll over Arthur Dent.

You're looking for something that's not there. Well, if it is there then either your experiment is flawed or you've made the greatest discovery in physics, ever. I'd go for the first option.

Regardless, I want to do the experiment and figure out the mechanics of it all.

I utterly agree and support that aim. You will learn lots from doing this, and, I hope, have an enjoyable experience.

20

Precisely. You are looking for a change in the propagation speed of an electromagnetic depending on the orientation of a transmitter in space. The change is zero.

However it is quite easy to see what sort of change you could detect from your equipment by simply looking at the smallest signal change you can measure then see what length that corresponds to and dividing that by the wavelength of your transmitter. That ratio is the same ratio the speed of light will need to change over 90 degrees of orientation.