At 4:30, static fields travel at c also; you simply don't notice because they are exactly the same after the wave passes. It is only after the field changes (due to charge motion) that you can watch how that change propagates. At 5:15, the reason you need an antenna is to match free space's impedance to the transmission line's impedance; otherwise, you get reflections and resonance energy buildup in the transmission line instead of efficient radiation. Also, not all transmission lines have 50 Ohm impedance. At 6:00, radiation patterns result from wave interference (diffraction) from different parts of the antenna. Antennae are fed from discrete points with distinct phases. These phases are delayed by the time it takes to reach another part of the antenna, If many of these waves are in phase at a distant point, you get strong radiation; you get weaker radiation as these phases vary more.
Yes but it seems that the antenna properly matched would be a load and the wave would heat the antenna and just sit there. does a resistor radiate? There is some very complex equations that would explain why the field lines cannot cross (boundary condition in one or two Maxwell equations) and then are forced to merge then move away. the diagram is very simplistic as this all happens at a tiny space. the EZNEC breaks up the wire into many segments to model this. I guess it looks about the same at a small distance. near field and far field will be very different. I probably learned this 40 years ago but I probably knew enough to pass the test and still did not fully understand.
@@IMSAIGuy A large part of matching is the resonance in the antenna. Resonance amplifies the voltage (and charge separation) by Q. This separated charge generates a dipole electric field. Similarly, the resonance amplifies the current needed to exchange the dipole polarity by Q and generates a magnetic field. Each of these fields propagate at light speed. Since each of these fields store energy, the energy is radiated away instead of dissipated as heat. (This is the classical picture; the QM picture is approached a bit differently.)
The answer why the antenna radiates energy is due to the fact that the speed of light (electromagnetic radiation) is finite rather than infinite, coupled with the fact that the charges in the wire are undergoing acceleration. See, for instance, the video, “Understanding Electromagnetic Radiation! | ICT #5”, beginning at one minute into the video. This shows a nice animation of the Figure 3.10 in the book, along with a verbal explanation. The field out in space can’t instantaneously adjust to the changes in field being produced by the antenna, and the field out in space can’t instantaneously collapse. Impedance matching and resonance are completely secondary to the cause of the radiation. Any unshielded conductor experiencing a changing current (acceleration of charges) will radiate energy to some extent. In fact, the output circuit of a transmitter is rarely conjugately matched to the impedance presented by the antenna and transmission line. We don’t want maximum power transfer. If we try for maximum power transfer, we are likely to burn up or vastly shorten the life of the transmitter. Instead, we want to get out the rated power, or less, from the transmitter while achieving maximum power conversion efficiency in the transmitter to it doesn’t overheat. 🙂
This is some more great stuff........love it!!!!! Next, can we do more on grounding, ground loops. and such. just an idea!!! Keep up the great vids.......each and every one is educational!!!
Used to be connect an old fashioned 6V light bulb in series with the transmitter antenna for RC model and tune up for max brightness - magical sight of light bulb illuminating without a closed circuit.
@IMSAI Guy. - I think the answer to the question as to why the em waves 'depart' from the aerial is resonance itself. In the same way it will be 'excited' by energy at its resonant frequency, it will also 'make a noise' if excited by energy at its resonant frequency, just like the good olde glass & choir singer experiment/demo... 73 de m1daz.
Agree … I was a ham for 35 years and never understood “electromagnet radiation” till I read the explanation in this book. Quite the lightbulb moment for me.
This might be completely wrong, please correct me if so: Any change in the electric field creates a wave, a disturbance that propagate. It’s the same as if you move a string on a violin. When you move the string in one point the neighbouring points will also have to move, and their neighbouring points, and so on, and a wave forms. An antenna is just a structure that resonates at a certain frequency so that you get a standing wave where the electric (and magnetic) field changes back and forth. And therefore it creates a continuous wave at some specific frequency.
I’ve used many antennas that, on paper, shouldn’t work. One in particular, for 160m, works incredibly good. I’ve contacted all 50 states and over 80 countries. I firmly believe that it’s all about capture area, the larger the better, combined with some simple impedance matching.
@@spicemasterii6775 180 ft of wire, end fed running horizontal, vertical and diagonal. Use it with an antenna tuner and I’m able tune all bands through 160m. Average height is about 20ft. I put it up as an experiment and it’s been up for 5 years.
As a retired engineer I have always regretted not fully understanding Maxwell's equations. I was good at math, but for some reason the way Maxwell was presented it did not stick. There was only the chalk board at the time - no real simulation nor ECAD programs to see the resulting fields etc. At this time my math is rusty as hell. I suppose it could be resurrected with some effort. My career never required EM - so mostly it got lost in the way unused brain cells shrivel up. Maybe you can motivate ? LOL, maybe not.
Really interesting to hear you muse on the same things that I find confusing. Why is free space 377Ω? And why do I want my antenna to be 50Ω? I get your point that math is not as essential to playing with electronics (or even designing electronics) as universities suggest. But I really enjoy seeing how advanced math can relate to real world observations. I had no idea there was an application of Poincare spheres to antennas. Now I have a reason to learn about that! I think where universities fail is by not connecting the theory to the application. I've talked with EE's who somehow don't think to apply Ohm's law to real life circuits. Somehow their education just fails to connect those dots
Is this the Bob Zavrel book? I worked with Bob for a few years making EEG acquisition equipment work in the MRI environment. He wrote a book about antennas.
I like your honest talk. You say lot of things you know but you say what you really dont and seem very good questions. I study Nikola Tesla work and compare with things like you mention in your videos and others and also books. Its fascinating how character and everything changes with higher electrical potential. Lot of people dont observe that they just consider only certain very limited conditions when they talk about radio and antennas. For example Tesla was mostly considering surface of conductor in his patents prefering exposed and oval surface and polished conductors and he used transformers as antennas as obviouslly he was working on wireless energy transmition. Which is interesting to observe transformers as antennas. I learned basics from Tesla patent on Radio. He sent energy to rc boat over radio waves and store it in condesers. Toise are all basics that taught me how oscillators work and how matching resonance of circuit are produced and how local oscilator works. Those are all basic that I ever failed to learn from others today. Most coveralage of those subjects today beat you with abstract mathematics and does not teach you clearly about it. Its mystified. I recreated some simple Tesla power meter where he used a tube with two conductors with coils aranged in wheatstone bridge as very precise measuing curent. I connected all my instruments over LXI and made program to collect data and in some cases it has shown to be more detailed in measurement then Rigol PSU. I learned so much from that experiment. I rembered your video on RF bridges that are basically Wheatstone bridge.
Beer bet: Why is the number 377 important to both power engineers and antenna engineers? 377 ohms is Z0, impedance of free space. 377 radians per second is 60 hz.
Nice review IMSAI Guy. Another book I like is Joe Carr's antenna handbook. I miss Carr, he was a legend. One of my other favorites is William Orr's Radio Handbook. Years ago I read a book that described the radiation from an antenna similar to blowing a soap bubble. The ring is necessary to generate the bubble , but it propagates through the air independently. Not quite accurate but as a kid I thought interesting. BTW any chance of you doing more optics and especially optoelectronics tutorials.
@@IMSAIGuy I have been doing photoelectric experiments using laser diodes and high power leds . Both visible and IR. With your physics background, it would be interesting to get your thoughts on using optics to maximize the optical path and minimize light attenuation. Here is a short video of an earlier experiment. th-cam.com/video/QlbgWLQ-XYQ/w-d-xo.html
Yes, why DO those photons jump off the antenna? It has always tormented me. I'm in the middle of the VHF contest now and they seem to be staying in my wire! 73
An antenna is impedance transformer from the transmission line Z to 377 Ohms.
"I know enough to be a little bit dangerous" is my new motto :-)
I love your videos, never stop sharing those golden nuggets
At 4:30, static fields travel at c also; you simply don't notice because they are exactly the same after the wave passes. It is only after the field changes (due to charge motion) that you can watch how that change propagates. At 5:15, the reason you need an antenna is to match free space's impedance to the transmission line's impedance; otherwise, you get reflections and resonance energy buildup in the transmission line instead of efficient radiation. Also, not all transmission lines have 50 Ohm impedance. At 6:00, radiation patterns result from wave interference (diffraction) from different parts of the antenna. Antennae are fed from discrete points with distinct phases. These phases are delayed by the time it takes to reach another part of the antenna, If many of these waves are in phase at a distant point, you get strong radiation; you get weaker radiation as these phases vary more.
Yes but it seems that the antenna properly matched would be a load and the wave would heat the antenna and just sit there. does a resistor radiate? There is some very complex equations that would explain why the field lines cannot cross (boundary condition in one or two Maxwell equations) and then are forced to merge then move away. the diagram is very simplistic as this all happens at a tiny space. the EZNEC breaks up the wire into many segments to model this. I guess it looks about the same at a small distance. near field and far field will be very different. I probably learned this 40 years ago but I probably knew enough to pass the test and still did not fully understand.
@@IMSAIGuy A large part of matching is the resonance in the antenna. Resonance amplifies the voltage (and charge separation) by Q. This separated charge generates a dipole electric field. Similarly, the resonance amplifies the current needed to exchange the dipole polarity by Q and generates a magnetic field. Each of these fields propagate at light speed. Since each of these fields store energy, the energy is radiated away instead of dissipated as heat. (This is the classical picture; the QM picture is approached a bit differently.)
The answer why the antenna radiates energy is due to the fact that the speed of light (electromagnetic radiation) is finite rather than infinite, coupled with the fact that the charges in the wire are undergoing acceleration. See, for instance, the video, “Understanding Electromagnetic Radiation! | ICT #5”, beginning at one minute into the video. This shows a nice animation of the Figure 3.10 in the book, along with a verbal explanation. The field out in space can’t instantaneously adjust to the changes in field being produced by the antenna, and the field out in space can’t instantaneously collapse.
Impedance matching and resonance are completely secondary to the cause of the radiation. Any unshielded conductor experiencing a changing current (acceleration of charges) will radiate energy to some extent. In fact, the output circuit of a transmitter is rarely conjugately matched to the impedance presented by the antenna and transmission line. We don’t want maximum power transfer. If we try for maximum power transfer, we are likely to burn up or vastly shorten the life of the transmitter. Instead, we want to get out the rated power, or less, from the transmitter while achieving maximum power conversion efficiency in the transmitter to it doesn’t overheat. 🙂
This is some more great stuff........love it!!!!! Next, can we do more on grounding, ground loops. and such. just an idea!!! Keep up the great vids.......each and every one is educational!!!
Used to be connect an old fashioned 6V light bulb in series with the transmitter antenna for RC model and tune up for max brightness - magical sight of light bulb illuminating without a closed circuit.
@IMSAI Guy. - I think the answer to the question as to why the em waves 'depart' from the aerial is resonance itself.
In the same way it will be 'excited' by energy at its resonant frequency, it will also 'make a noise' if excited by energy at its resonant frequency, just like the good olde glass & choir singer experiment/demo...
73 de m1daz.
Agree … I was a ham for 35 years and never understood “electromagnet radiation” till I read the explanation in this book. Quite the lightbulb moment for me.
This might be completely wrong, please correct me if so:
Any change in the electric field creates a wave, a disturbance that propagate. It’s the same as if you move a string on a violin. When you move the string in one point the neighbouring points will also have to move, and their neighbouring points, and so on, and a wave forms.
An antenna is just a structure that resonates at a certain frequency so that you get a standing wave where the electric (and magnetic) field changes back and forth. And therefore it creates a continuous wave at some specific frequency.
there are some similarities but they end pretty quickly.
I’ve used many antennas that, on paper, shouldn’t work. One in particular, for 160m, works incredibly good. I’ve contacted all 50 states and over 80 countries. I firmly believe that it’s all about capture area, the larger the better, combined with some simple impedance matching.
What antenna is that? If you don't mind sharing
@@spicemasterii6775 180 ft of wire, end fed running horizontal, vertical and diagonal. Use it with an antenna tuner and I’m able tune all bands through 160m. Average height is about 20ft. I put it up as an experiment and it’s been up for 5 years.
I've got a copy of that exact ARRL antenna book , refer to it all the time !
As a retired engineer I have always regretted not fully understanding Maxwell's equations.
I was good at math, but for some reason the way Maxwell was presented it did not stick. There was only the chalk board at the time - no real simulation nor ECAD programs to see the resulting fields etc. At this time my math is rusty as hell. I suppose it could be resurrected with some effort. My career never required EM - so mostly it got lost in the way unused brain cells shrivel up. Maybe you can motivate ? LOL, maybe not.
90% math/physics 10% Blackmagic as I was taught in tech school.
The standard ratio is 20% / 80% 😉
When in reality is the other way around...
80% magic is my number
Really interesting to hear you muse on the same things that I find confusing. Why is free space 377Ω? And why do I want my antenna to be 50Ω?
I get your point that math is not as essential to playing with electronics (or even designing electronics) as universities suggest. But I really enjoy seeing how advanced math can relate to real world observations. I had no idea there was an application of Poincare spheres to antennas. Now I have a reason to learn about that! I think where universities fail is by not connecting the theory to the application. I've talked with EE's who somehow don't think to apply Ohm's law to real life circuits. Somehow their education just fails to connect those dots
Hi! You are really touching the interesting points! I think I know from you how the 50 Ohm has been chosen (75 for receiving and 25 for transmit)
Never knew such book existed without "real" math perquisites needed for antennas...
Is this the Bob Zavrel book? I worked with Bob for a few years making EEG acquisition equipment work in the MRI environment. He wrote a book about antennas.
yes
I like your honest talk. You say lot of things you know but you say what you really dont and seem very good questions. I study Nikola Tesla work and compare with things like you mention in your videos and others and also books. Its fascinating how character and everything changes with higher electrical potential. Lot of people dont observe that they just consider only certain very limited conditions when they talk about radio and antennas. For example Tesla was mostly considering surface of conductor in his patents prefering exposed and oval surface and polished conductors and he used transformers as antennas as obviouslly he was working on wireless energy transmition. Which is interesting to observe transformers as antennas.
I learned basics from Tesla patent on Radio. He sent energy to rc boat over radio waves and store it in condesers. Toise are all basics that taught me how oscillators work and how matching resonance of circuit are produced and how local oscilator works. Those are all basic that I ever failed to learn from others today. Most coveralage of those subjects today beat you with abstract mathematics and does not teach you clearly about it. Its mystified.
I recreated some simple Tesla power meter where he used a tube with two conductors with coils aranged in wheatstone bridge as very precise measuing curent. I connected all my instruments over LXI and made program to collect data and in some cases it has shown to be more detailed in measurement then Rigol PSU. I learned so much from that experiment. I rembered your video on RF bridges that are basically Wheatstone bridge.
Would you discuss Jacksons Classical Electrodynamics as a follow on?
That would be no
I like how you missed those finite element analysis equations.
That is my same first antenna book, 1977 edition as I recall. {edited to add first}
Antennas are black magic! I was given an ARRL Antenna book, it looks scary!🤯
Beer bet: Why is the number 377 important to both power engineers and antenna engineers?
377 ohms is Z0, impedance of free space.
377 radians per second is 60 hz.
You can get the 3rd edition in Kindle format......
Nice review IMSAI Guy. Another book I like is Joe Carr's antenna handbook. I miss Carr, he was a legend. One of my other favorites is William Orr's Radio Handbook. Years ago I read a book that described the radiation from an antenna similar to blowing a soap bubble. The ring is necessary to generate the bubble , but it propagates through the air independently. Not quite accurate but as a kid I thought interesting. BTW any chance of you doing more optics and especially optoelectronics tutorials.
I've done some stuff. what optics/electro tutorials are you interested in?
@@IMSAIGuy I have been doing photoelectric experiments using laser diodes and high power leds . Both visible and IR. With your physics background, it would be interesting to get your thoughts on using optics to maximize the optical path and minimize light attenuation. Here is a short video of an earlier experiment.
th-cam.com/video/QlbgWLQ-XYQ/w-d-xo.html
I've created a playlist 'optics' that should interest you
I've checked on Amazon, some idiot wants like $11,000 for the first edition paperback )))
Yes, why DO those photons jump off the antenna? It has always tormented me. I'm in the middle of the VHF contest now and they seem to be staying in my wire! 73
Am I safe in assuming that this is an ARRL publication ?
yes
SWEET BABY GANESHA! $326 US on Amazon!!!
home.arrl.org/action/Store/Product-Details/productId/132743
$35
@@IMSAIGuy Thank you. I'll buy ten and cut you in on the Amazon profits!
The A R R L Antenna Book is written by whom can please replay on, thanks
here is the latest version: home.arrl.org/action/Store/Product-Details/productId/114288
I am one of the pro-Math/Physics people
Hand Wavy :)
tnx ur good explanation for all issues 73 de ta1bj
Very unusual for a computer guy to ACTUALLY KNOW ANYTHING TRULY TECHNICAL! WONDERFUL!