Naked Science Forum
On the Lighter Side => Science Experiments => Topic started by: hamdani yusuf on 23/11/2020 07:37:57
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Continuing my effort to understand the behavior of microwave in another thread, here I'd like to share experiments showing how radio wave behaves. I've prepared some experimental equipment, but didn't have enough time to execute the experiments yet, so for now I'll put this well made video from Harvard Natural Sciences Lecture Demonstrations first.
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Here is another demonstration from a documentary movie.
Credits: Artifax Production for Channel 4 - 1990
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My plan is to repeat those experiments with various shapes and materials of antennae. I hope it can complete our understanding of how radio waves work. In my previous experiments using microwave, we investigated its interactions with various combination of materials and shapes, but the transmitter and reciever antennae have fixed materials and shapes.
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I was about to start the experiment using these generic 433 MHz radio transmitter and receiver,
(https://www.componentsinfo.com/wp-content/uploads/2020/02/fs1000a-XY-MK-5V-433mhz-module-pinout.png)
and the circuit diagram (transmitter on the right)
(https://i.stack.imgur.com/fwySK.gif)
when I realized that their antenna feeds are unbalanced, which are not well suited for dipole antennae. Using monopole antennae is simple and convenient for practical use, but they introduce unwanted complexities which are against the purpose of the experiments. After searching for a while I finally found this source which I think is the best solution for the problem.
http://vk5ajl.com/projects/baluns.php#current
CORE TYPE CURRENT BALUN
Highly recommended. This is a very low loss balun and ideal for use with a tuner.
This balun works by controlling currents. THERE IS NO TRANSFORMER ACTION. The two windings must be in the same sense (dots at the same end). The magnetic fields of opposing balanced working currents will cancel each other out and so present very little impedance (other than the resistance of the wires) to these currents. On the other hand, common mode currents will produce a mutually inductive magnetic field and face a high impedance.
This means the more turns the better, up to a point. In this case, the windings are a transmission line that has losses but these are much lower than the losses transfering energy from one winding to another through a core.
Design considerations are really very minimal. Since the losses of balanced lines are low compared to coax, you aren't losing much except for the resistance of the wires which is very low compared to radiating resistance anyway.
The current balun shown here, wound around a steel bolt, is probably a little crude but why not? Steel or iron is not normally used for RF because there are too many eddys making it too inefficient for transformers. In this application, since there is no magnetic effect for the desired currents, it doesn't matter. For common mode currents on the other hand, inefficiency is an advantage. Not only is a high impedance presented to common mode currents, the energy from them is absorbed by the bolt.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fvk5ajl.com%2Fprojects%2Fimg%2Fbaluncurrent.jpg&hash=16c45fd1879c937ac5e005e0e27514de)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fvk5ajl.com%2Fprojects%2Fimg%2Fbalcur.jpg&hash=925370e17330b815fafca72eff314eca)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fvk5ajl.com%2Fprojects%2Fimg%2Fbalbolt.jpg&hash=f7ad38a8e0108abaedb6355b42c53ddb)
I'd like to hear if someone here has a second opinion.
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I was about to start the experiment using these generic 433 MHz radio transmitter and receiver,
Since I only need continuous radio signal, just like in microwave experiment, I simply connected the data pin of the transmitter to vcc 5V, which is supplied by a USB charger. The data pin of the receiver was measured by a Voltmeter. The reading shows only a few milli-Volts. Connecting or disconnecting power supply of the transmitter doesn't change the result.
So, I measured the Voltage of each pin of the transmitter.
I found something strange happened. The vcc, which was connected to USB charger measured above 200V. I checked the voltmeter using other power sources and it was fine. The vcc still read 200V for a few minutes, and then suddenly it went back to normal 5V.
The data pin of the receiver never shown any difference in voltage whether or not the transmitter was powered up. So I think I'll just replace them with another model.
Unfortunately I didn't recorded it in a video. Does anyone have any idea what happened? Maybe I should not directly connected the data pin with Vcc?
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I'd like to hear if someone here has a second opinion.
The bolt will be a very poor core for a radio frequency signal.
The eddy current losses will be huge.
But using a bolt to form the two coils is a neat idea.
If you cover the outside of the coils with tape to hold them in place and then "unscrew" the bolt from them, leaving an air cored transformer, that will work better
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The data pin of the receiver never shown any difference in voltage whether or not the transmitter was powered up. So I think I'll just replace them with another model.
So I just bought another package, which includes :
1pcs STX882 433MHz ASK Wireless RF Transmitter Module
1pcs SRX882 433MHz ASK Wireless RF Receiver Module)
2pcs SW433-TH32DN (433MHz Nickel Plated Spring Antenna)
STX882 is a ASK transmitter module with small size, ultra high power, low harmonics. With high stability, it can be achieved at 50mW power when the voltage is 3.6V, it is the maximum
ransmitter power module under the the same voltage in the market. Data port of the module can be connected to the microcontroller directly, make wireless product development and production more convenient.
Features:
- Frequency Range: 433/315 MHZ
- ASK modulation mode
- Small volume low self radiation
- High-power long-range
- Frequency stability
- Various international testing standards
SRX882 ASK Wireless Remote Control
----------------------------------------------------
Superheterodyne Receiver Module
SRX882 is a superheterodyne receiver with micro power and strong driving force, is supplementary STX882 / STX888 module. Data port of the module can be connected to the microcontroller directly, make wireless product development and production more convenient.
Features:
- Frequency Range: 433/315 MHZ
- ASK /OOK modulation mode
- Super anti-power interference
- Low-power sleep less than 1uA
- Low self radiation
- Small size
- Frequency stability and reliability
- Various international testing standards
(https://ecs7.tokopedia.net/img/product-1/2018/9/30/374410/374410_68ee5542-d370-478f-84fd-ef335dcf79c6_800_800.jpg)
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I connected the power supplies, a USB power bank for transmitter and a USB charger for receiver. Both are around 5.1 Volts DC. The data pin of the transmitter is connected to Vcc through 1kOhm resistor. The data pin of the receiver is measured using a Voltmeter relative to ground.
No significant voltage was measured, either in DC nor AC mode. The Voltmeter only shows significant value when the transmitter was turned on or off, but then fell back to near 0. This is not what I'm looking for.
So I checked the datasheet of the receiver chip.
https://html.alldatasheet.com/html-pdf/1161402/PTC/PT4303/61/1/PT4303.html
(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=80985.0;attach=32140;image)
(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=80985.0;attach=32142;image)
It looks like I can exclude the OOK/ASK demodulator by measuring output of buffer amplifier at pin #5 instead of data pin #11. What I want to measure is the raw radio signal amplitude.
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My initial test shows that the Voltmeter showed voltage of 1.7 VDC on pin #5 when only the receiver was turned on. When the transmitter was also turned on, the voltage increased to around 1.9 VDC.
The transmitter was moved away from receiver, and the voltage decreased accordingly. I knew I was going in the right direction.
I want the voltmeter shows 0 when the transmitter is off. This can be done by changing the voltage reference from ground to 1.7V, which can be achieved using a potentiometer as voltage divider. The measurement would then have a range from 0 to around 200 mV.
I measured the received radio signal with various transmitter position and distance from receiver. I also tried to block the transmission using aluminum plate I used in microwave experiment. I'll upload the video when I'm done.
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For initial tests, I used as much original components as possible, just to see if the devices are working as intended. I used spring antennae provided in the package for both transmitter and receiver. The signal was measured for various position and distances between transmitter and receiver. It was also measured when an aluminum plate was introduced as additional obstruction. I finished taking the video clips, and now moving on to editing phase.
Unlike my previous experiments using laser and microwave which have directed transmission, the radio transmitter and receiver used omnidirectional antennae. They make it susceptible to interference from reflection by surrounding environment. The spring antennae add more complexities in making prediction of the results.
In the next video I'll use dipole antenna to simplify the radio transmission pattern, and try to control the reflective environment.
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I want the voltmeter shows 0 when the transmitter is off. This can be done by changing the voltage reference from ground to 1.7V, which can be achieved using a potentiometer as voltage divider. The measurement would then have a range from 0 to around 200 mV.
It turns out that it's hard to stabilize the voltage divider using potentiometer alone. A slight movement can change the voltage significantly. So I put additional resistors to reduce the slope of V/R curve around the desired value.
(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=80985.0;attach=32160;image)
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The latest tests I've done using spring antennae are exploring the effect of waveguide using aluminum pipe. Compared to waveguide in microwave, this time it seems more leaky. Perhaps it's because the size of the pipe is much smaller than the wavelength of the radio wave.
I also tested the transmission of radio wave when the transmitter and the antenna are wrapped by several layers of aluminum foil. Of course, the circuitry including antenna has been wrapped first using clear tape to prevent short circuit. It greatly reduces the wave transmission at long distances, but when the transmitter and receiver antennae are very close (a few cm away), the transmission can still be pretty strong. It looks like the aluminum foil wrap can't act as a good Faraday cage for this frequency.
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Did you wrap the power supply / battery in aluminium?
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Did you wrap the power supply / battery in aluminium?
No. There was USB cable coming in from a power bank to the transmitter.
(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=80985.0;attach=32174;image)
The reciever can be seen on top right corner.
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My latest update on this matter. I covered the whole parts of the transmitter, including power cable and battery. The cable was folded, stuck to the battery. No signal was detected by the receiver.
Some part of the battery was exposed, and still no detection.
It seems like the cable acted as antenna. As long as it's covered, the radio can't propagate properly.
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Here is my first video investigating behavior of radio wave. It shows the preparation phase by constructing radio transmitter and receiver, also the obstacles I met and how to overcome them.
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I hope I can investigate the difference between near field and far field EM wave soon.
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Here is the functional test of the transmitter and receiver pair.
Before going for more sophisticated setup, I want to make sure that the system works as intended. So I'll go first with the original package, besides those modifications I mentioned previously.
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Here is the test using an aluminum plate as obstruction. The size of the plate is less than the wavelength of the radiowave. With frequency or 433 MHz, the wavelength is almost 70 cm, while the side of the plate is just around 20 cm. So, it's expected that the blockage is only partial.
The result looks normal as expected until 1:00.
But if we compare to what happened in previous experiments using partial reflector in microwave transmission, the result is still consistent.
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It's been so long since the last time I experimented with radio frequency. I have one that hasn't been edited and narrated. There I measured the signal strength around a long antenna, which is more than one wavelength. I hope to finish it soon so I can share it here.
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Using monopole antennae is simple and convenient for practical use, but they introduce unwanted complexities which are against the purpose of the experiments. After searching for a while I finally found this source which I think is the best solution for the problem.
http://vk5ajl.com/projects/baluns.php#current
CORE TYPE CURRENT BALUN
Highly recommended. This is a very low loss balun and ideal for use with a tuner.
This balun works by controlling currents. THERE IS NO TRANSFORMER ACTION. The two windings must be in the same sense (dots at the same end). The magnetic fields of opposing balanced working currents will cancel each other out and so present very little impedance (other than the resistance of the wires) to these currents. On the other hand, common mode currents will produce a mutually inductive magnetic field and face a high impedance.
This means the more turns the better, up to a point. In this case, the windings are a transmission line that has losses but these are much lower than the losses transfering energy from one winding to another through a core.
Design considerations are really very minimal. Since the losses of balanced lines are low compared to coax, you aren't losing much except for the resistance of the wires which is very low compared to radiating resistance anyway.
The current balun shown here, wound around a steel bolt, is probably a little crude but why not? Steel or iron is not normally used for RF because there are too many eddys making it too inefficient for transformers. In this application, since there is no magnetic effect for the desired currents, it doesn't matter. For common mode currents on the other hand, inefficiency is an advantage. Not only is a high impedance presented to common mode currents, the energy from them is absorbed by the bolt.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fvk5ajl.com%2Fprojects%2Fimg%2Fbaluncurrent.jpg&hash=16c45fd1879c937ac5e005e0e27514de)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fvk5ajl.com%2Fprojects%2Fimg%2Fbalcur.jpg&hash=925370e17330b815fafca72eff314eca)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fvk5ajl.com%2Fprojects%2Fimg%2Fbalbolt.jpg&hash=f7ad38a8e0108abaedb6355b42c53ddb)
I'd like to hear if someone here has a second opinion.
I found another model of balun for dipole antenna.
(https://yc3lsb.files.wordpress.com/2009/10/hfdipol.png)
I'd like to know how it will perform compared to previous model.
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Meanwhile, I've just finished editing my old recorded video. It's a short one, demonstrating the effect of wave guide in radio transmission.
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Did you wrap the power supply / battery in aluminium?
You can find out here.
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There's one more experiment I've recorded before the receiver was dismantled because I needed the multimeter and power bank. It shows the transmission profile of a long transmitter antenna, which is more than one wavelength. I've finished editing the video. I'll share it with you soon.
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This video demonstrates transmission profile of long transmitter antenna in radio frequency.
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I've recorded some videos experimenting on radio wave using dipole antenna. I think it will give us access to explore further on polarization, wave direction by phase shifting, and some other phenomena which are harder to demonstrate using spring antenna.
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The outcomes of your experiments will be in accordance with Maxwell's equations.
What are the experiments/ videos for?
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The outcomes of your experiments will be in accordance with Maxwell's equations.
What are the experiments/ videos for?
To understand the factors need to consider in applying the theories, identify the practical difficulties in using them, and the limits of applicability. How else would you get those information?
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How else would you get those information?
Look at all the experiments that have been done in the past.
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How else would you get those information?
Look at all the experiments that have been done in the past.
I haven't found the experiments that I'm going to do.
“It's impossible for a man to learn what he thinks he already knows.”
― Epictetus
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I've recorded some videos experimenting on radio wave using dipole antenna. I think it will give us access to explore further on polarization, wave direction by phase shifting, and some other phenomena which are harder to demonstrate using spring antenna.
Here's the first video using a dipole antenna. More videos will follow.
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Why don't Submarines use Radio or GPS?
This video contains many interesting technical information which are usually discarded in the movies.
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When several different phenomena occurred at once in an experiment, the results may seem like magic.
It takes ingenuity to untangle them and identify the phenomena causing effects there.
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Why don't Submarines use Radio or GPS?
Submarine use both radio and GPS. It is true they go rather long periods of time without being able to have radio or GPS contact.
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As BC has already pointed out radio waves behave exactly as Maxwell's equations predict, no more, no less. Any experiment one can think of will already have been done, countless times. Radio is one particular of physics that has received a colossal amount of experimentation.
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As BC has already pointed out radio waves behave exactly as Maxwell's equations predict, no more, no less. Any experiment one can think of will already have been done, countless times. Radio is one particular of physics that has received a colossal amount of experimentation.
Lorentz' force can't be derived from Maxwell's equations.
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True, but I think the outcome will be consistent with Maxwell's eqns.
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True, but I think the outcome will be consistent with Maxwell's eqns.
This assertion is where my concern lies.
Maxwell's equations predict, no more, no less.
Lorentz' force and Coulomb's force describe how matters behave under influence of electromagnetic radiations, which Maxwell's equations alone don't predict.
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This assertion is where my concern lies.
Feel free to do experiments though, as Alan pointed out, the experiments were probably done a hundred years ago.
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It would be interesting to do experiments mentioned in the articles below.
https://en.wikipedia.org/wiki/Faraday_paradox
The Faraday paradox or Faraday's paradox is any experiment in which Michael Faraday's law of electromagnetic induction appears to predict an incorrect result. The paradoxes fall into two classes:
Faraday's law appears to predict that there will be zero electromotive force (EMF) but there is a non-zero EMF.
Faraday's law appears to predict that there will be a non-zero EMF but there is zero EMF.
Faraday deduced his law of induction in 1831, after inventing the first electromagnetic generator or dynamo, but was never satisfied with his own explanation of the paradox.
https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction#Exceptions
It is tempting to generalize Faraday's law to state: If ∂Σ is any arbitrary closed loop in space whatsoever, then the total time derivative of magnetic flux through Σ equals the emf around ∂Σ. This statement, however, is not always true and the reason is not just from the obvious reason that emf is undefined in empty space when no conductor is present. As noted in the previous section, Faraday's law is not guaranteed to work unless the velocity of the abstract curve ∂Σ matches the actual velocity of the material conducting the electricity.[30] The two examples illustrated below show that one often obtains incorrect results when the motion of ∂Σ is divorced from the motion of the material.
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It would be interesting to do experiments mentioned in the articles below.
The experiments were interesting- so people did them.
Here's the first video that Google found for me.(I don't know if it's any good- it just shows that the experiments have been done).
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It would be interesting to do experiments mentioned in the articles below.
The experiments were interesting- so people did them.
Here's the first video that Google found for me.(I don't know if it's any good- it just shows that the experiments have been done).
I've seen this video not long after it was uploaded.
What's interesting is the conclusions of the video from 5:28 onward aren't widely accepted, refuted, nor even discussed.
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This is an interesting experiment you can do to demonstrate the radio wave generated by high tension lines. You can also measure the polarization angle of the radio wave.
High Tension Line Radiation Detector!
Ok, here is a simple device that you can build, with a 3D printer, to measure the radiation coming off the high voltage, high tension lines.. that are running though your local neighborhood... just a couple of dipole antenna and a neon light bulb.. and you can be drawing in power from the air! Yes I am calling this radiation.. some might consider this near field coupling... but lets not spit hairs! The fields are intense... and definitely penetrating you body! Fun science project! See my thingiverse page, for the free STL file.. to print your very own High Tension Line Radiation Detector!!
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I just found another use of radio wave.
Strong Perseid Meteor Echo
A good quality echo, registered at the end of the Perseid meteor stream, in the Summer, showing an intense trail that remained almost uninterrupted for 45 seconds.
http://hebweather.net/meteor-echoes/
What you can hear and see in this continuous waterfall display (the technical term) are meteor echoes, caused by the reflection of radio waves on the hot ionised air that a meteor leaves behind after it disintegrates while entering Earth?s atmosphere.
The most active daily period is the one that precedes sunrise (GMT time zone), but echoes can be seen and heard at any time of the day, more of them during the meteor showers. As long as the waterfall continues scrolling, there is a possibility of registering a meteor echo. Sometimes, satellites are also detected, and the International Space Station is almost regularly observed.
The signals will appear in the area between 1040 and 1100Hz, marked on the top white band by the big horizontal square bracket. The constant background sound is simply noise, while the meteor echoes will have a more high pitched tone, different from the base one. Furthermore, the longer and more complex an echo is, the longer and more intricate its sound will be.
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Detection of radio wave can be very simple.
Tuned Antennas Lighting Up LEDs
In this video, I demonstrate how resonant antennas which are cut to specific lengths, are able to light up LEDs, if you transmit on their resonant frequencies. For those who want an expanded description on how to build one of these antennas, please watch this video.