How Can We Improve Wireless Radio Modulation?
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- čas přidán 17. 05. 2020
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In this video, we will continue with where we left off discussing wave modulation in Part 1, “How does Wireless Radio Communication work?”, where we also discussed electromagnetism and how radio waves are transmitted and received. (realpars.com/wireless-communi...)
In this video, we will discuss radio modulation, what is pathloss and how to decrease it, line of sight propagation, path profiles, and path profile engineering.
Modulation is a technique of converting and mixing data into radio waves by adding this information to a carrier or base signal.
This is accomplished by a modulator in which, mixes the data signal with a carrier signal. A carrier wave is a wave of constant frequency, like a sine wave.
The now modulated and amplified signal which emanates from the antenna propagates through the air towards the receiving station antenna where the modulated signal is demodulated, separating the data from the carrier signal.
So, in other words, modulation alters the shape of a carrier wave to encode the speech or sound and data information we want to be transported by hopping on a normal signal wave.
A wave can be identified by its frequency, measured in oscillation per second, its wavelength measured in units of lengths, and its amplitude or power measured in “dB” or “m”.
This means the wavelength is inversely proportional to frequency, in that, the longer the wavelength, will result in a lower frequency. Or, the shorter the wavelength, will result in a higher frequency.
There are essentially three basic types of modulation.
The difference between these modulation methods is how the carrier wave is modulated, hence altered.
Amplitude (or AM) modulation is where the amplitude of the carrier signal is modulated or changed in proportion to the data signal.
And with Frequency (or FM) modulation, the frequency, or the number of times per second the wave changes direction determines how the carrier signal is modulated or altered.
Ok, now let’s discuss how far a radio wave will travel or propagate, and what are the elements interfering, or attenuates, the signal, with a brief introduction to pathloss.
The transmitter radiates a signal having a specific power based on the size and type of an antenna. The signal as it travels begins to weaken or attenuate based on the environment and landscape the signal travels. The phenomenon known for how the electromagnetic wave weakens is known as pathloss.
The receiver only captures a certain portion of the signal based on the power used at transmission and depending on the different obstructive factors, such as distance or free space, obstacles such as buildings and mountains for example.
As electromagnetic waves propagate and travel further and further away, the initial power at which the transmitted signals spreads out over a large area. In the beginning, the entire transmitted power is confined to a small spherical area or bubble.
To illustrate the degradation of the signal, if the receiver is close to the transmitter it will capture more power and if the receiver is further away from the transmitter the receiving antenna can only capture a smaller fraction of the transmitted power.
There are several parameters involved with attenuation, they are distance, wavelength, and the transmit power.
Pathloss (or L) depends on distance and wavelength.
Power loss is the weakening of the signal no matter how much power is transmitted.
How can we overcome path loss? One way is to use an RF Line-of-Sight tool.
Check out this free online tool from SCADACORE at:
(bit.ly/Line-of-Sight)
The RF Line-of-Sight tool is very helpful in mapping long-distance radio communications for remote SCADA monitoring remote sites and data acquisition applications.
The online tool considers antenna height and the topographical patterns of the earth to calculate the line-of-sight of a radio path.
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Other things to consider are:
Antenna selection: Picking the wrong antenna is just about as bad a leaving it off in the first place. You would be better off with a coat hanger. There's a ton of stuff to consider, so find yourself a good antenna guy. And pick one that is familiar with your specific application, A WiFi guy might be a poor choice for example. Depends on what you are doing.
Coax cable: Losses don't start at the antenna, any coax that you use, ranges from pretty good to fairly lossy. Choose wisely.
Application: A point-to-point connection doesn't have to worry about where the receiving radio is going to be located tomorrow (except in the event of roving bands of pillaging Ham Radio operators). For these applications, a high gain directional antenna (e.g. Yagi, Cantenna) would be a great choice since it directs most of the transmission in one direction. Think of the difference between a light bulb and the focused beam of a flashlight.
Applications where you are trying to communicate with mobile equipment wouldn't be able to take advantage of this. For these applications, look into radios that can do MIMO.
Frequency: For applications where you will be communicating with equipment in a building with lots of metal, the higher frequencies are a very poor choice. However, 900 Mhz or 433 Mhz (depending on which country that you plan on placing the installation) are great choices for excellent propagation. A 1 watt 900 Mhz radio for example can hit 30 Km easily, a 433 Mhz radio, more so.
Do your homework: Here in the states, 900 Mhz is legal for non-licensed use. 433 Mhz is not (depending on the power). Do a site survey to see if the site is already using the spectrum that you wish to use. Just because the frequency is non-licensed doesn't mean that you get to step on each other.
Great observations and comments. In control system applications, a site survey is always completed, since most of the applications are within the boundaries of a plant or inside production facilities, and beyond signal interference, the site study can be used to determine if internal structures, equipment, or other potential obstructions will be probematic.
@@realpars Thanks! And thanks for the great videos!
As for the site surveys, yeah we both know it has to be done. But the toobnoobs might not. :) They certainly will on their second installation...
BTW, there are cheap spectrum analyzers that can be used to do a site survey, for the RF spectrum usage in any case. For Traffic, collisions, overlap, etc, analysis you would want to have a formal survey. I've got a SDRPlay that I will try out the next time I go down to the plant. It's a really nice SDR, fairly cheap, and there is a spectrum analyzer package for it.
As for squeezing in another radio system at a site that already is using that spectrum, switching the polarity of the antennas from what the site is using would certainly help out in keeping unwanted signals at bay.
And I would be remiss if I didn't mention that while the range of the lower frequency radios is superb, the data rate isn't. So don't expect live HiDef video from your AdaFruit LoRa 900Mhz. LOL!
Excellent!
Thank you, Bob!
Good information
thanks for all your great work!!!
in context to the topic
can explain emi ( communication cable shielding ) how its used and what its importance?
Thanks for the topic suggestion, I will definitely go ahead and forward this to our creator team. Happy learning!
Informative
Awesomely simple & short 👍🏻
Glad to hear that! Happy learning.
@@realpars In process...😁👍
Hi RealPars, I love your channel. It's the best I've seen in automation and instrumentation.
I have a question regarding wireless data transfer technology. What module can be used to carry a wired instrumentation and transfer that data to control room; ie, to bring the signals from the 4-20 mA transmitters to the module and the module is able to transfer via wireless that information to control room. Thanks!
Siemens SCALENCE W products can be used to transmit wired I/O rack information wirelessly. Many other manufacturers (MOXA, Acromag, Omron, Advantech) provide suitable hardware as well. Typically the local wired I/O is transmitted using a wireless bridge to a wireless gateway that is connected to the main control system, with data transmitted wirelessly between those two devices.
I enjoy your videos guys
Happy to hear that, Derin!
Explain how signal wave and carrier wave are added/modulated/transformed inside the modulator, how is that done specifically? And how is the carrier wave removed by the demodulator? What exactly happens in there and by what?
Hey!
Thanks for your comment and your suggestion. I will pass this on to our course developers!
Thanks for sharing and happy learning!