# Measuring Radio Wave Frequencies and Signal Strength

#### Nugheblord

Joined May 1, 2020
1
Hi, I am new here and excited to find this place with so many like-minded people. Cheers.

I have found a new interest in wireless electronics and so many questions are coming to mind. Lately, I've been trying to imagine what radio waves look like. I have a good image in my head but i would like to see what is going on around me if only with measuring devices.

Is it possible for a device to tell me what signals and frequencies are being conducted around me? For instance, my wireless keyboard keeps getting disconnected. It would be awesome to see what frequency it is using and be able to turn it off and see if that frequency is still being used by something else.

I would also love to be able to see the (probably) hundreds of radio transmitters sending out signals around me from every phone, computer, cell tower, etc.

Is there a device that will do all this?

#### MrChips

Joined Oct 2, 2009
21,400
Welcome to AAC!

You can buy an RF spectrum analyzer for under US$200 on ebay. A good used unit can run US$3000 and more.

Joined Jan 15, 2015
5,513
Spectrum Analyzer as mentioned with a wide bandwidth (covers a wide range of frequencies). Really neat instruments and also even used a good one is expensive but like I said swept spectrum analysis is really cool.

Start simple and cheap with nsaspook's suggestions.

Ron

#### sparky 1

Joined Nov 3, 2018
265
The closed circuit only engineers will disagree with those who study both open and closed systems. The frindge science are yet another set. In all I have found most have a mixture of views sometimes leaning toward what works for them and prefer not to explore what has not been accepted by lower level academia. I read a student from India being severely told he was wrong because he described waves in a semiconductor as a liquid flow. The various media types can have different terminology to convey a physical description. In the real world the boundary condition can include waves so fast that most instruments do not sense. The challenge to explore electrical waves in space has been slow. That avenue called "The electric universe" has made some progress to find answers that go beyond the engineers level. So the challenge to educate EE has this Pandora's box.

#### be80be

Joined Jul 5, 2008
2,047
SDR set simple and cheap with nsaspook's suggestions.
Thats why I got one about 3 years ago I have a lot of little transmitters
From 300 mhz to 900 something that I wanted to see them talk LOL
I figured a SDR be the way to go I got mine for 10 bucks on bang good.

It works really good to see where there at in mhz and there decoding software too thats next on my list of things to do.
Right now i'm working on a antenna that I seen on the net

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#### HughJazscheens

Joined Dec 29, 2019
4
Imagine a vertical pole that is an antenna. Imagine a vertically-polarized wave whose height matches that of the antenna, and is created by electrical waves being exposed to the antenna. Imagine also a horizontally-polarized wave that is magnetic, and it's width is the same as the antenna's height. When the electrical wave and magnetic wave are combined, you're looking at a radio wave. An electromagnetic wave whose wavelength is ideally matched precisely to the length of the antenna. If you need to use the same antenna for a slight range of frequencies (say, 88 to 108 mHz for a hobby FM transmitter), you tune the length to the middle of the range to do as well as you can. Or tune it to the exact frequency you'll be using. Anything less is a compromise and generates wasted signal as heat and may be responsible for unwanted interference.
The frequency of the waves is the channel on your receiver. A receiver simply excludes all unwanted channels and then amplifies whatever's left -- the one you want. There are a couple of ways to discriminate unwanted signals.
The antenna will work better if you also have an effective ground to "bounce" the signal off of. This can be the Earth or metal lengths called radials. The electromagnetic wave only exists if there is a ground reference to compare it to. Imaging charging your body to 15,000 volts of static electricity to play a prank on a friend. If he has also charged his body to 15KV, there is no discharge because there is no reference. This is how a bird can sit on a 110,000 volt wire with no effect. There's nothing to reference it to.
Your antenna will work best if it is oriented the same as the receiver's antenna. Your router's wifi antenna works this way, so if you have two antennas, set one vertical and one horizontal.
If the antenna is only half as long as the radio waves, you have a half-wave antenna. If it's one-fourth the length, it's a quarter-wave antenna. These will work better than a length that is not a simple fraction, but not as well as a full-wave antenna. (CB radios used 5/8-wave antennas around 18' tall because they could not legally be higher than 20 feet above their mount.) So, an AM radio transmitter full-wave antenna at 1 mHz (or 1,000 kHz, the middle of the band) is too long to be practical (300 meters, or 1,000 feet). A wifi or Bluetooth antenna (at 2.4 gHz, or 2,400 mHz) is full-wave at just under 5 inches (120mm).
Sometimes you can have perfectly acceptable results with a random length of wire, and there are tools for "tuning" that to work better by artificially modifying the electrical length. For a transmitter, full-wave is best.
Portable AM radios use a special "loopstick" antenna that cannot be modified to increase it's ability. However, a trick known as "inductive coupling" can be used. Simply wrap some wire around the entire radio and extend it in a perpendicular orientation to the transmitter (form a T-shape between the signal and the wire). Cars have special circuits so the AM and FM radios can share the same antenna length.
Hams sometimes use a "trap" antenna. It has multiple coils of wire stacked along the length of one antenna. Each radio band requires a radically different antenna length, so the signal finds a compatible length of antenna using each coil. If they want to use a band that can be bounced off of a layer in the atmosphere, they orient the elements to be horizontal instead of vertical. This lets them "skip" their wave past the horizon. Once it reaches the Earth, it can bounce again, repeating around the globe. This only works after dark, when the sun no longer alters the E-layer in the stratosphere. This is why you can pick up distant AM radio stations after dark, but FM (frequency is 100 times higher) doesn't work over 50 miles. This is also why police and emergency services use UHF (even higher yet) so they don't get interference from a police car in another state. High frequencies punch right through the E-layer and go into space.
I'm unaware of any instrument that will "display" these events. YouTube has a lot of videos for you.
However, your smartphone can install an app named WiFiAnalyzer that will give you clever graphics showing the strength and channels on local wifi signals. Your keyboard may be Bluetooth. If you find a neighbor is on the same wifi channel as you, switch to another channel (Google it).
You can find a great deal of info in the annual ARRL Handbook (Amateur Radio Relay League). This is the bible for ham radio operators.
AM signals (above and below the AM radio band) transmit a powerful signal (carrier wave) and then add a weaker second wave that carries the actual sound (amplitude modulation). Signals above 50 mHz (old broadcast TV channel 2) are usually FM (except for aircraft, who use a band above the FM broadcast band, but for legacy purposes, still have an AM signal). FM works by altering the frequency of the signal to match the frequency of the sound (frequency modulation). This is why FM has no static. IF you want to know about FM stereo (multiplexing) and color TV signals, there's plenty to learn.

#### SamR

Joined Mar 19, 2019
2,261
A fun little exercise is to place a short (5-10") piece of wire in your oscilloscope probe and start waving it around your desk/bench. You will be surprised at the signals you will find. One of the noisiest items on my bench is an LED lamp?!?! LEDs don't make noise! True, but LED PWM dimmers do. Surprise! Keyboards can also be noisy, switch mode power supply in your computer is noisy but has a Faraday cage around it plus the grounded computer case to stop the noise. WIFI, AM, FM, UHF, VHF, you name it. We live in an electromagnetic swamp on a planet constantly being bombarded with noise from "space". Such is nature...

#### sparky 1

Joined Nov 3, 2018
265
Amplify and move a lower band to a higher band.
If you build a wide band amplifier and include it on a probe with a coax cable you can sniff out most anything.
By amplifying you will find there are many more that hidden weaker signals. If you want to see a representation of those signals, The SDR will work. If the frequency is too low you can mix it with a higher frequency for example a 100 Mhz oscillator mixed with a very low or an extra low frequency VLF or ELF then the product will appear at an offset from 100 Mhz plus or minus. This is called frequency translation. If you let 100 Mhz represent zero then a 1Mhz signal would appear at 101 Mhz or 1 unit from zero.
The IC known as NE602 possibly obsolete now but still around, the NE612 would work also this is a mixer it likes about 100mV or less so again the sniffer probe amplifys the signal the NE602 mixes it and your SDR is now capable of very incredible inventory scaled signals formatted correctly with relative strength scaled up so you can see the hidden world of signals around you.
Another example of frequency translation is listening to sounds beyond human hearing (using a microphone) to what dogs can hear and even the sonic sounds of bats. I can listen to the atmosphere before a storm there are plenty of unusual sounds and one sdr does it all.

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#### SamR

Joined Mar 19, 2019
2,261
The NE602 and NE612 are now also SMD as SA602 and SA612

#### MrAl

Joined Jun 17, 2014
7,673
Hi, I am new here and excited to find this place with so many like-minded people. Cheers.

I have found a new interest in wireless electronics and so many questions are coming to mind. Lately, I've been trying to imagine what radio waves look like. I have a good image in my head but i would like to see what is going on around me if only with measuring devices.

Is it possible for a device to tell me what signals and frequencies are being conducted around me? For instance, my wireless keyboard keeps getting disconnected. It would be awesome to see what frequency it is using and be able to turn it off and see if that frequency is still being used by something else.

I would also love to be able to see the (probably) hundreds of radio transmitters sending out signals around me from every phone, computer, cell tower, etc.

Is there a device that will do all this?
Well these days it may require more than just knowing the frequency you will also have to know the twist orientation because there could be something like 55 channels being transmitted on a single frequency with a technology called OAM radio.
I guess it is the answer to finding more air space for radio transmissions as the bands get used up.

#### nsaspook

Joined Aug 27, 2009
7,356
Multiplexing an OAM wave is possible because the spiral shape like a drill bit has empty space between the 2 flutes.
The filtering has become more compact and lower cost because of meta material. Test were made public in 2013 so it can be discussed to some degree.
OAM “Twisted Light” is IMO snake-oil. It's never been demonstrated to have far-field bandwidth beyond the classical electromagnetic context modulation like input-multiple-output (MIMO) transmission used today.

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0056086
In this paper we address a fundamental physics question: Can modes with non-zero angular momenta representing extra, beyond N = 2, independent communication channels be radiated to the far field and selectively picked up by a proper antenna, which is insensitive to standard plane wave modes? If the polarization is circular–a common situation in wireless technology–one has N = 2 with plane waves in the two polarization modes phase-shifted by 90°. Thus it is clear that up to N = 2 orthogonal plane wave polarization modes can exist in the far field and the circularly polarized mode carries angular momentum. Yet to date whether a greater number of angular momentum modes can exist at the same frequency and carrying independent signals in the far field has not been shown to violate fundamental physical principles.
...
Rather than analyzing the theoretical treatments for errors, we use another approach to prove that the hypothesis that independent communication channels based on orbital modes can be selectively picked up by a proper antenna that is insensitive to standard plane wave modes violates the Second Law of Thermodynamics, which states that it is impossible to construct a perpetual motion machine of the second kind. First let us specify the necessary conditions that are essential for the utilization of the M-th orbital mode as a parallel independent information channel:
https://spectrum.ieee.org/telecom/wireless/twisted-light-could-dramatically-boost-data-rates

https://en.wikipedia.org/wiki/Orbital_angular_momentum_multiplexing
As of 2013, although OAM multiplexing promises very significant improvements in bandwidth when used in concert with other existing modulation and multiplexing schemes, it is still an experimental technique, and has so far only been demonstrated in the laboratory. Following the early claim that OAM exploits a new quantum mode of information propagation, the technique has become controversial, with numerous studies suggesting it can be modelled as a purely classical phenomenon by regarding it as a particular form of tightly modulated MIMO multiplexing strategy, obeying classical information theoretic bounds.

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#### sparky 1

Joined Nov 3, 2018
265
Comment is extreme to gut a small company \$3.9 billion on a public forum. All research can offer something.
There are many other carrier arrangements. The reply to the point made was that SDR has limitations, that is correct.
First, What is OAM? geez! forum comments like that can cause big problems. The merit was not expressed.
I really feel for the scientist studying it and reading that rant.

My friend was doing circular polarizing had to listen to negative view points He still had fun and learned what he could.
Some laughed at the funny looking antenna and made ignorant comments, later developed funny antenna syndrome. His wife told him so.

For SDR at extremely high frequencies the amount of front end detection or band translation modifications would be ludicrous at the present time. Most of the communications R&D have a niche and are viable in those applications. I feel that if it works don't fix it but tracking the bad guys is a challenge. Also the variety of different spread spectrum technologies also can be used for crime, they should be used to fight crime.

SDR has downside. getting into others property or being hacked.
A hacker RF can use SDR to record an automobile's key fob signal he can then open the car door, grabs belongings and be gone before anyone suspects. But it is the man that decided to use it for crime and not the SDR itself it will continue and a few will ruin it for everyone else.
At this time you can still own an SDR but like scanners taken off the market. It is technology crime that lowers our personal freedom ..

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#### nsaspook

Joined Aug 27, 2009
7,356
That changes nothing. OAM is a perfectly valid technology like classical EM polarization (spin angular momentum SAM) that must also obey basic laws of physics in that #1 you don't get something for nothing in symbol expression per Quantum of EM energy as effective degrees of freedom (EDOF)
Orbital angular momentum (OAM) multiplexing technique has recently emerged and generated
widespread interests since the OAM was discovered as a property of electromagnetic wave and acoustic
wave. It was widely acknowledged that OAM multiplexing can achieve very high effective degrees of
freedom (EDOF) and improve the spectral efficiency in optical, radio and acoustic communications.
However, in the field of free-space optical (FSO) communications, it was demonstrated that OAM
multiplexing is not the optimal multiplexing technique and the spatial bandwidth product (SBP) limits
the EDOF. Is there any EDOF limits of OAM multiplexing in radio and acoustic communications? Could
OAM multiplexing be safely scaled to far field? Here, we discover that the azimuthal resolution of
OAM mode generator in OAM multiplexing limits its EDOF. Furthermore, we also verify that the OAM
multiplexing in radio and acoustic communication fails to enable a long distance transmission and high
EDOF simultaneously incurred by the inherently imperfect OAM mode generator.
Conclusion Thus far, we discuss the physical resources of UCAs and the EDOF of OAM multiplexing in radio and acoustic communications. We discover that the physical resources of UCAs, used both as OAM mode generator and detector, comprise of the the azimuthal resolution and radial resolution. Te former limits the number of effective OAM modes and the later limits the radial intensity variation. Since the mutual orthogonality of OAM modes derives from the transverse helical phase pattern exp(−ilφ) which only depends on the azimuthal phase variation, the maximum of EDOF of OAM multiplexed communications is equal to the azimuthal resolution of UCA. If multi-ring UCAs are implemented as transceivers, the maximum EDOF of OAM multiplexed communications is less than conventional MIMO’s. In practical OAM multiplexed communications, due to the inevitable flaws of real UCAs, the near-field negligible faw will induce a significant EDOF decay in far field. More generally, even the UCA is perfectly arranged, the OAM modes will always be disturbed by ambient noises, such as turbulent medium, refraction and refection, all of which cause the OAM modes imperfect. Therefore, the performance of far-field OAM multiplexing is unsecured. As far as we can perceive, one method to mitigate such effect is to use the lower order OAM modes as data carrier, but this will lead to the loss of its advantages in performance. Given that, the OAM multiplexing might be improper in far-field radio and acoustic communications.
https://arxiv.org/pdf/1808.02462.pdf
A. Towards a Complete Mode Set
Very recently, it was pointed out that OAM multiplexing is not an optimal technique for free-space information encoding and that OAM itself does not increase the bandwidth of optical communication systems [256], [257]. Miller in [258] demonstrated through calculations, based on the singular value decomposition (SVD) of the coupling operator between transmitting and receiving sources [259], that there are better optimal choices than using different OAMs to increase the capacity of optical communication. The main output of the study is that OAMs could be outperformed by any complete modal basis to scale the capacity of a communication system.
https://iopscience.iop.org/article/10.1088/1367-2630/17/4/043040
The conclusion is that the use of modes with angular momentum will not 'open' any previously unexploited degree of freedom. LG modes or other modes with angular momentum are simply orthonormal mode sets among others. The use of modes carrying OAM will not increase the channel capacity, neither in waveguided nor in free-space communication links. The OAM modes performs no worse, but also no better than any other set of orthogonal modes. In certain applications OAM mode multiplexing is already starting to be exploited [79], although broadcasting is neither a typical nor a suitable one for reasons that will become evident below.
...
5. Conclusions
On the basis of Weyl's law it is clear that the mode density of modes carrying OAM has the same scaling with frequency, angular frequency or wave vector as, for example, a plane wave set of modes has. From this we conclude that the angular momentum carried by electro-magnetic waves does not increase the channel capacity compared to a mode set void of OAM. (Such a mode set can be constructed from equally weighted sums and differences of angular momentum modes with opposite chiralities). Using one set of eigenmodes one codes the information in another degree of freedom than with the other set, but the number of power-orthogonal modes (or 'channels') per unit frequency bandwidth remains the same. This argument is also supported by thermodynamical considerations.

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#### sparky 1

Joined Nov 3, 2018
265
I don't want to argue with you any more NSA Spook I don't care. I have better things to do then argue good bad polarized here polarizing there. It is offensive to push a narrative that is off subject The merits are not being stated by me (the thread is about monitoring waves)I really want to end. It is obnoxious to continue to push your strong opinion. I believe you must have a history of making people uncomfortable and think you fooling yourself that it is justified. First someone comments about OAM then the subject is diverted by strong continuous assertions by NSA SPOOK on discrediting a company and causing ruckus.

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#### nsaspook

Joined Aug 27, 2009
7,356
I don't want to argue with you any more NSA Spook I don't care. I have better things to do then argue good bad polarized here polarizing there. It is offensive to push a narrative that is off subject The merits are not being stated by me (the thread is about monitoring waves)I really want to end. It is obnoxious to continue to push your strong opinion. I believe you must have a history of making people uncomfortable and think you fooling yourself that it is justified. First someone comments about OAM then the subject is diverted by strong continuous assertions by NSA SPOOK on discrediting a company and causing ruckus.
Man, mello out dude. You posted "Test were made public in 2013 so it can be discussed to some degree", so I did.
and now, because enough time has passed to validate some of the original questions about the technology.

Sorry if I upset your apple-cart.

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#### Janis59

Joined Aug 21, 2017
1,187
Spectrum analyser functionality is also inside the EMI measurer GQ-390 from zero to 2,4 GHz. However it have few blindspots inside the frequencies where no regular transmitters may have no rights to transmit. Other method is SDR where the cheap stick is option between 1 MHz and 1,7 GHz and other much expensive named HackRF1 between 50 kHz and 2,7 GHz. However any SDR have a problem it`s sensitivity is relative thing being not calibrated. Of course any may provide own calibration by means of GQ-390 but then probably all the job may be done by it. Actually, in the range much below of shortwaves just the frame with few hundreds of turns may be used in complect with standard RF spectrometer.
RE: ""Is it possible for a device to tell me what signals and frequencies are being conducted around me? For instance, my wireless keyboard""
Ultimatively GQ-390