That is so cool! I've never seen RF power measured at different positions along a transmission line like that. I guess it's no surprise that it works, but it's always nice to see theory shown with an oscilloscope probe and a steady hand.
***** If only there was a means by which you could collaborate and share data in real time over long distances. I long for the day when that becomes reality.
This video is the absolute gold standard for demonstrating standing waves. A wiki page is one thing, but seeing the RF power minima and maxima being measured on an actual transmission line is quite another. Fantastic work W2AEW! 73 de W6PGS.
Thanks Allen. I remember when we did this experiments when I was an undergrad during one of my courses in the lab, I had a "WOW!" moment which changed my perspective forever. :)
***** Can you make a video explaining type 1 through 3 op amp compensation networks used for switch mode power supplies? Also, what does the "s" mean in (s+1) term in control theory for compensators and what does the H(s) function stand for?
EETechs H(s) is the transfer function of the loop expressed using LaPlace transforms. This would be a more complicated topic and would likely have to encompass a few videos. I'll put it on the list though.
I'm starting to think that utube is much better form of education than the universities. They never explained it this good at my U. In my case it was like here take this bunch of formulas, plug in numbers, calculate, congrats here's your bachelor's.
Unfortunately, I wasn't a very good student (and that's my fault), but I do think Alan's videos are much more educational than any lectures I received in my EE baccalaureate degree program; my lab classes didn't even use real oscilloscope probes (and, I had no knowledge what additional influences a home-made probe would have introduced , when high frequencies were used in a circuit- besides, we didn't have the equipment to generate anything over 200 megahertz, anyway, if my memory serves me well). We just used coaxial cables, stripped to the conductor on one end, with a BNC connector on the other end. It's embarrassing for me to admit, how much basic electronic science I've learned from Alan's videos - that I should have already know from my formal education as a EE student. I sure hope my university does a better job today educating future engineers - but, I doubt they do, since I can't imagine the lab classes having expensive modern electronic test equipment in them (too expensive). It blows my mind to think of the money wasted in education, when they could just buy some decent test equipment, and pay the correct people to demonstrate how to properly use the test gear - and what the equipment is measuring, and why; And I do believe in the idea of public education, and consider myself to be very much a liberal. However, just today I was reading, in our local paper, about our local convention center receiving an education award for educating children middle school and high school children- not sure of the exact grades; this convention center puts on these very silly plays, which are supposed to be comical (I guess), for which they bus in thousands of kids to watch, during the school day, and call this science education. I started watching one of the plays concerning science, and it was a joke (truly a joke), IMHO.
That was a terrific visualisation of an effect I understand, but had never witnessed so clearly. I've watched many of your fabulous videos, Alan, but this one has somehow eluded me. Glad to see it today. Thank you.
Your organized thought, visual aids and practical application is spot-on to me. So many You Tubers want to race through a subject without coming up for air. Also, you don't seem to have the tendency of diving down rabbit holes to the point where I feel I've been through a spin cycle! I rarely have to pause your videos either. I revisited this vid because memory is always the first thing to go!
Fantastic presentation. Back in the day, we saw similar demos using "Letcher" wires. Nothing can be more informative than actually seeing the reality of the electric waves in their natural habitat, so to speak. Well done. In all of your videos, you have proven yourself to be a great teacher.
Excellent practical demonstration of SW. I used to have students experience wave additions in the floor with 'super' slinkies. Similar wave behavior in different wave mediums makes understanding wave behavior so interesting.
Wow, I've never been able to see the effects of impedance matching as directly as you measured it here. It's very cool that you were able to measure the nodes and antinodes. Time to break out some PCBs and give it a try!
Amazing demo on Standing waves. Actuall measurement of the standing wave pattern on the live transmission line is absolutely unique. Much appreciated W2AEW !
To be able to "see" practically what the text books teach, is just amazing. It really helps to take the information on board. Thanks. You have so much content, I'm working my way through. Watch one, think and absorb, watch another... I could be half educated by the end of this! LOL
Brilliant!! Never really understood this. Now I do !! You definitely have a gift for breaking apart the complex and showing us what is really going on.
Nice demo. I have a large slotted line and an HP 415E I use to demonstrate SWR. If the crowd is very large, I hook a small amp and speaker to the amp output of the 415E so the 1000Hz tone can be heard around the room. I usually get some comments about the archaic equipment. Then I like to point out that this is the type of network analyzer that was used to design the equipment that brought back TV signals from the moon walks.
Ohhh man! That was awesome to see. I am literally learning about standing waves in my electromagnetics class right now. My brain started hurting so I stopped to watch some youtube. I just happen to type in standing waves and got this video. So nice to see what they are talking about in my EM book. All the equations and derivations just make you blind. This really helps me understand what is going on.
Well I feel like an infant listening to their first words! OMG! Some cool stuff here! I understood about 50% of it, but I took what I could from your words of wisdom! Thanks!
I've had great trouble in the Electromagnetics course because while using Smith charts, we never went over what the transmission and reflection coefficients, nor the VSWR actually represented visually. Thanks so much for clearing this up.
Thanks for letting me see this phenomena. Although yuur previous video spoke of it, it was tough to believe it. This video gives the edge. Thank you so much.
I don't know how you do it. I could read for a week on all this voodoo magic, and you Sir, sum it all up in 10 minutes. Your channel is one of the best I have have subbed.
Excellent demonstration. This would have been good at my tech-college. It took me ages to understand this straight off a blackboard, in a class of semi-interested students.
Amazing video as always, I was having a discussion with a friend of mine as to why the normalized impedance would repeat itself on a transmission line every half wavelength. This proves it. Also that is true for any termination except matched termination aka 50 ohms in most cases. Sits really well with the smith chart also. Alan you are true genius.
In the '70s I saw a professor run a light bulb between two conductors energised with a WWII 10 cm radar unit and watched the bulb get brighter and dimmer as he traversed the length. Now I've seen the effect twice!! Cool!!
Thanks so much again Alan. I wish I had your vids and ideas for test fixtures when I was teaching Engg. Techs. Standing waves are one of the hardest ideas to grasp so I sent this link to my basic ham class. And so happy that the classic Similarities of Wave Behavior is on TH-cam too. Cheers
I wish we had videos like these when they taught waves & antennas in college. All the test equipment were costly, we did not have time, and the teacher wasn't really interested because we could not visualize it! but it looks so cool :)
Hello Alan. Thank you for your time spent making these videos. In your summary at 10:15, if we can relate that a mis-termination of a transmission line as being an antenna that does not have a reactive, capacitance property of 50 Ohm at the frequency of operation. As well as not having our transmission line from the antenna to our SWR meter at 1/2 wave increments to the Velocity Factor of the coax, would only mean that we would not be able to truly see what are VSWR actually is. For example, if our main run is a random length of coax and we tune an antenna to the coax with the swr meter in our shack, although the swr meter is showing a reasonable swr it doesn't mean our antenna is a 50 ohm termination. Effectively not radiating power from the antenna but the coax as well diminishing the Effective Radiated Power. On the other hand, if we were to have our main run from the antenna to our SWR meter in increments of a 1/2 wave length at the frequency of operation to the Velocity Factor of the coax. Only then would we be able to tune our antenna to the lowest VSWR possible (or as close to 50 ohms as possible). Maximizing our Effective Radiated Power. Make sense?
First point of clarification - there is a mis-termination if the antenna does not have a *RESISTIVE* impedance that is equal to the transmission line impedance (not a reactive or capacitive property). If the antenna presented a 50 ohm capacitive reactance, it would have a very high SWR. The "magic" of a half-wavelength transmission line is that the impedance looking into the line will be equal to the impedance looking into the load (antenna in this case). In other words, the load impedance is replicated when the line is a multiple of half wavelengths long. A longer or shorter transmission line will result in a change in the impedance looking into the line, but does NOT change the SWR on the line. This is a very important statement to grasp - changing the line length does NOT change the SWR, it just changes the complex impedance seen looking into the line. This is illustrated pretty well in one of my videos on the smith chart (th-cam.com/video/ImNRca5ecF0/w-d-xo.html). Of course, this is assuming negligible loss in the transmission line. So, having the transmission line be not equal to a multiple of half-wavelengths long *only* means that the input impedance does not match the antenna impedance - but the SWR is still unchanged! The SWR is a function of the antenna impedance and the transmission line's characteristic impedance, *NOT* the line length. Therefore, if you make adjustments to an antenna to minimize SWR, the result will work fine regardless of line length (as long as the transmission line is not electrically part of the antenna). Bottom line, it is NOT necessary to have the transmission line be a multiple of 1/2 wavelength in order to get maximum radiated power (maximum power transfer to the antenna).
@@w2aew Clarification noted! If I am reading this correctly (Cuz I aint lernt to good) The "magic" of a 1/2 wave length coax is, that it is no longer seen by the transmitter. Poof, It disappears (not taking into account losses in the coax) Ta-da! Magic! To my understanding, the transmitter now sees the antenna only, and if the antenna dos not have a 50 ohm impedance a Standing Wave will be educed on the line and seen by the swr meter. You have made it clear in other videos that a 1/4 wave transmission line looks like a short.(it is also mentioned in the MFJ analyzers manual) Which means the impedance value of our transmission line does change BASED ON length of line with respects to frequency applied. so using a random length of coax while making a 1/4 wave ground plane antenna affects the tuning of the antenna, while trying to make the antenna terminate our line at 50 ohms. Making the coax electrically part of our antenna. (an experiment that everyone can do) If I build a 70 cm 1/4 wave ground plane antenna with a random length of coax, which works perfectly fine with minimal SWR at my house and I give it to my friend for Christmas (cuz i'm such a nice guy) and he uses his own coax, which is a different length and Velocity Factor (then what I made and tuned the antenna with) his SWRs will be totally different than mine. Now, the stipulation to this (in my opinion) is if I give him the antenna WITH the coax (in which i'm really not that nice of a guy) that i made and tuned the antenna with originally and he needs to extend the length of the coax to get to his swr meter. He would need to make a coax jumper in increments of half wave lengths. That would mean that the coax I give him IS Electrically part of the antenna (which is now a 50 OHMs to the end of the coax not to the connection at the antenna) and the extension he needs to make will not be seen by the swr meter because it is in 1/2 wave multiples. Poof, Ta-Da, Magic !! If I would have originally used a length of coax that was multiples of 1/2 wave lengths to the frequency of operation and velocity factor of the coax, The home brew 1/4 wave ground plane antenna, would have an impedance of 50 ohms at the connector.
(End experiment) To to sum it up (in my opinion), 1/2 wave increments of coax is the only way to do things, when setting up a station. Unless an antenna tuner is used. Even then, the work done in the transformation of impedance by a tuner would be less if 1/2 wave increments were used to and from the tuner (the transmitter will not see the coax only the tuner and the tuner would not see the coax, just the impedance mis-match of/at the antenna) That could only be proven with a VNA in which I don't own. Alan, I would like to make something clear. I am not trying to negate, manipulate, argue, dispute anything you are saying or showing us in your video. I really do appreciate the work you have done and your time spent making your videos. The one thing that you have done is sparked further curiosity and ambition on working towards discovery and understanding. I thank you for that.
@@sevenoseven8494 I'm afraid you misunderstood me! The *only* thing that the 1/2 wavelength increment gives you is a replication of the antenna impedance at the coax input. There is NO REASON to restrict yourself to this!! You can use any length you need. If the antenna is matched to the coax, all is well with any length coax. If the antenna is not matched to the coax, the input impedance to the coax won't be 50 ohms, but can still be matched at the transmitter end with a tuner, regardless of coax length. The SWR on the line in this case will be the same - regardless of the coax length. Restricting to 1/2 wavelength increments does not make the tuner's job any easier. The complex impedance looking into the coax will vary with the coax length, but the SWR is the same.
@@w2aew I'm sure I do understand you, It seems we are standing a quarter wave apart on a smith chart looking towards the center, both trying to achieve a 50 Ohm Impedance. 1) you state, The only thing that the 1/2 wavelength increment gives you is a replication of the antenna impedance at the coax input. my response, that's my point! I want to make sure that my antenna has an impedance of 50 Ohms not my coax and antenna! 2) you state, There is NO REASON to restrict yourself to this!! My response, It's not a restriction, having the main run to the antenna in 1/2 wavelength increments, would not be adding the complex impedance of the random length coax to the miss-matched complex impedance of the antenna, further complicating the total complex impedance of the antenna and coax. Why make things more complex then what they should be. the antenna impedance would be the cause of the miss-match on the system creating the SWRs. 3) you state, If the antenna is matched to the coax, all is well with any length coax. My response, If that's the case, I can use RG6 75 Ohm coax trough out my shack. Adjust the angle and length of the ground plane of my antenna to compensate for the impedance and affect the angle of radiation of the antenna. Rendering the antenna useless. Achieving a flat SWR. 4) you state, If the antenna is not matched to the coax, the input impedance to the coax won't be 50 ohms, but can still be matched at the transmitter end with a tuner, regardless of coax length. My response, That's exactly what the purpose of doing things this way. Now I know that the antenna needs adjusting. That's it! Using a half-wave length of coax ensures that the transmitter/SWR meter see the antenna and not the coax and the antenna matches to the transmitter. 5) you state, The SWR on the line in this case will be the same - regardless of the coax length. Restricting to 1/2 wavelength increments does not make the tuner's job any easier. The complex impedance looking into the coax will vary with the coax length, but the SWR is the same. My response, I quote "The only thing that the 1/2 wavelength increment gives you is a replication of the antenna impedance at the coax input." any SWRs will be caused by the impedance miss-match of the antenna. It will show a similar complex impedance miss-match value (of the antenna) on a MFJ analyzer, as if the analyzer was plugged into the bottom of the antenna with no coax or separated by one 1/2 wavelength of coax or separated by multiples of a half-wave length of coax. Intern, showing me how close the antenna is to a 50 ohm impedance. Because the coax becomes less of a factor, aside for the losses of the coax. in which we have no control of.
My point is that you’re not adding any complexity when using non 1/2 wavelength increments. When using 50 ohm coax, minimum SWR occurs when the antenna is adjusted to 50 ohms, regardless of coax length. You don’t have to use 1/2 wavelength increments to know when you’ve adjusted the antenna to 50 ohms.
Outstanding demonstration of standing waves!
That is so cool! I've never seen RF power measured at different positions along a transmission line like that. I guess it's no surprise that it works, but it's always nice to see theory shown with an oscilloscope probe and a steady hand.
Brilliant demo and explanation. Thanks for sharing!
Applied Science Ben and Alan, you guys should meet up and do a video.
Frédéric Dutrey I would *LOVE* that - too bad we're at opposite sides of the country!
***** If only there was a means by which you could collaborate and share data in real time over long distances. I long for the day when that becomes reality.
Yeah, maybe when someone figures out this inter web thingy ;-)
Greetings from India, Alan you are my greatest RF guru
This video is the absolute gold standard for demonstrating standing waves. A wiki page is one thing, but seeing the RF power minima and maxima being measured on an actual transmission line is quite another. Fantastic work W2AEW! 73 de W6PGS.
one more animated visualization from me (made in HFSS) for coax line
ypylypenko.livejournal.com/42947.html
Thanks Allen. I remember when we did this experiments when I was an undergrad during one of my courses in the lab, I had a "WOW!" moment which changed my perspective forever. :)
The Signal Path Blog Yes, there's nothing like "seeing" things like this - really makes it "click!" Thanks for the comment!
***** Can you make a video explaining type 1 through 3 op amp compensation networks used for switch mode power supplies? Also, what does the "s" mean in (s+1) term in control theory for compensators and what does the H(s) function stand for?
EETechs H(s) is the transfer function of the loop expressed using LaPlace transforms. This would be a more complicated topic and would likely have to encompass a few videos. I'll put it on the list though.
Definitely booking marking this
This was fascinating. As a newish ham I never really got SWR until watching this. Thanks!!
Wow, I never thought that I'll ever witness RF Standing wave so practically.
I'm starting to think that utube is much better form of education than the universities. They never explained it this good at my U. In my case it was like here take this bunch of formulas, plug in numbers, calculate, congrats here's your bachelor's.
You just have to find youtube instructors that explain things in a way that works for YOU! I'm glad that my videos do that for you.
Unfortunately, I wasn't a very good student (and that's my fault), but I do think Alan's videos are much more educational than any lectures I received in my EE baccalaureate degree program; my lab classes didn't even use real oscilloscope probes (and, I had no knowledge what additional influences a home-made probe would have introduced , when high frequencies were used in a circuit- besides, we didn't have the equipment to generate anything over 200 megahertz, anyway, if my memory serves me well). We just used coaxial cables, stripped to the conductor on one end, with a BNC connector on the other end. It's embarrassing for me to admit, how much basic electronic science I've learned from Alan's videos - that I should have already know from my formal education as a EE student. I sure hope my university does a better job today educating future engineers - but, I doubt they do, since I can't imagine the lab classes having expensive modern electronic test equipment in them (too expensive). It blows my mind to think of the money wasted in education, when they could just buy some decent test equipment, and pay the correct people to demonstrate how to properly use the test gear - and what the equipment is measuring, and why; And I do believe in the idea of public education, and consider myself to be very much a liberal. However, just today I was reading, in our local paper, about our local convention center receiving an education award for educating children middle school and high school children- not sure of the exact grades; this convention center puts on these very silly plays, which are supposed to be comical (I guess), for which they bus in thousands of kids to watch, during the school day, and call this science education. I started watching one of the plays concerning science, and it was a joke (truly a joke), IMHO.
@@WECB640 I think Walter did a great job with the pendulum explanation.
You are very good at explaining somewhat hard to understand "things" in a way that makes them understandable. Thank you.
Michael Lloyd I agree. I've never saw anyone else do it as good as he does.
Amazing to actually see it in action! TY
That was a terrific visualisation of an effect I understand, but had never witnessed so clearly. I've watched many of your fabulous videos, Alan, but this one has somehow eluded me. Glad to see it today.
Thank you.
So great to see someone who knows the material explaining it well!
Your organized thought, visual aids and practical application is spot-on to me. So many You Tubers want to race through a subject without coming up for air. Also, you don't seem to have the tendency of diving down rabbit holes to the point where I feel I've been through a spin cycle! I rarely have to pause your videos either. I revisited this vid because memory is always the first thing to go!
This an excellent demonstration of VSWR. Thank you!
Best demonstration of standing waves so far, and a useful function of persistence on a digital scope. Thank you.
Fantastic presentation. Back in the day, we saw similar demos using "Letcher" wires. Nothing can be more informative than actually seeing the reality of the electric waves in their natural habitat, so to speak. Well done. In all of your videos, you have proven yourself to be a great teacher.
Excellent practical demonstration of SW. I used to have students experience wave additions in the floor with 'super' slinkies. Similar wave behavior in different wave mediums makes understanding wave behavior so interesting.
Great video! Really helped me in understanding transmission lines for a project I'm completing for my PhD. Much appreciated!
I dont think any body can explain this any better and any clearer than you have Alain. You've nailed it.
You make it so much easier to understand transmission line theory. It's pretty hard to visualise it just by reading about it.
Great video! SWR explained without getting drowned in formulas and theory etc. Loved every moment of it. Thanks!
Wow, your visualization methods help a lot to understand. Thank you!
Wow, I've never been able to see the effects of impedance matching as directly as you measured it here. It's very cool that you were able to measure the nodes and antinodes. Time to break out some PCBs and give it a try!
Amazing demo on Standing waves. Actuall measurement of the standing wave pattern on the live transmission line is absolutely unique. Much appreciated W2AEW !
I can't stop watching that video over and over again. you are the master of desk experiment.
In 10 minutes you've completely demystified standing waves for me. Thank you!
Thanks man. This does not only made me understand standing wave, but i now visualize the concept of transmission
You are a teacher that can do magic. Thank you for the effort you put in these teachings. Have you considered a teaching career?
Maybe I'll teach after I retire...
I like this practical literal demonstration of SWR stuff.
This is such a great intuitive explanation of things. Thanks so much!
To be able to "see" practically what the text books teach, is just amazing. It really helps to take the information on board. Thanks. You have so much content, I'm working my way through. Watch one, think and absorb, watch another... I could be half educated by the end of this! LOL
Brilliant!! Never really understood this. Now I do !! You definitely have a gift for breaking apart the complex and showing us what is really going on.
Genius again.
The best video i saw about stand waves.
Clear, direct and simple.
Sorry about my rusty english.
Huge 59 S9+40
73 DE pu2srz
Nice demo. I have a large slotted line and an HP 415E I use to demonstrate SWR. If the crowd is very large, I hook a small amp and speaker to the amp output of the 415E so the 1000Hz tone can be heard around the room. I usually get some comments about the archaic equipment. Then I like to point out that this is the type of network analyzer that was used to design the equipment that brought back TV signals from the moon walks.
Thank you for taking the time to demonstrate standing waves. Great work!
Ohhh man! That was awesome to see. I am literally learning about standing waves in my electromagnetics class right now. My brain started hurting so I stopped to watch some youtube. I just happen to type in standing waves and got this video. So nice to see what they are talking about in my EM book. All the equations and derivations just make you blind. This really helps me understand what is going on.
Thanks for sharing! I watched this video with my 9 year old and it got him excited to break out his littlebits.
Awesome visualization of standing waves as well as a description of constructive/destructive wave interference.
Best RF teacher on the planet!
That is the coolest thing i have ever seen. Illustrating standing waves with this trick was just amazing. Great thinking! Bravo!
Well I feel like an infant listening to their first words! OMG! Some cool stuff here! I understood about 50% of it, but I took what I could from your words of wisdom! Thanks!
I've had great trouble in the Electromagnetics course because while using Smith charts, we never went over what the transmission and reflection coefficients, nor the VSWR actually represented visually. Thanks so much for clearing this up.
Simply the best, this should be the supplementary video material for any transmission / Power related EE course
Thumbs up! Great video to visualize standing waves on TML. The first time that I have seen such a kind of visualization.
As usual you make a complex topic so much easier to visualize in real life! 73 - Dino KL0S
I like your video, thank you so much for this video😊
Thanks for letting me see this phenomena. Although yuur previous video spoke of it, it was tough to believe it. This video gives the edge. Thank you so much.
So awesome!! I'm studying about Transmission Lines right now and it's so cool to actually see all the theory presented in the books!
really great way to explain SWR.
I don't know how you do it. I could read for a week on all this voodoo magic, and you Sir, sum it all up in 10 minutes.
Your channel is one of the best I have have subbed.
Yes, yes exactly!
Excellent demonstration. This would have been good at my tech-college. It took me ages to understand this straight off a blackboard, in a class of semi-interested students.
Another awesome demonstration, Alan. - Thank you! - Jim
Amazing video as always, I was having a discussion with a friend of mine as to why the normalized impedance would repeat itself on a transmission line every half wavelength. This proves it. Also that is true for any termination except matched termination aka 50 ohms in most cases. Sits really well with the smith chart also. Alan you are true genius.
Best explanation and practical demonstration ever! 4 thumbs up.....
Fantastic video. so much knowledge compressed in only 10 mins.
In the '70s I saw a professor run a light bulb between two conductors energised with a WWII 10 cm radar unit and watched the bulb get brighter and dimmer as he traversed the length. Now I've seen the effect twice!!
Cool!!
Thanks Alan, every time I watch one of your vids I know more about RF theory, I really like your practical illustrations of this sort of thing.
Thank you Gerry!
Perfect demo, 5 stars (cannot be explained better).
Beautifully and perfectly illustrated.
Thanks so much again Alan. I wish I had your vids and ideas for test fixtures when I was teaching Engg. Techs. Standing waves are one of the hardest ideas to grasp so I sent this link to my basic ham class. And so happy that the classic Similarities of Wave Behavior is on TH-cam too. Cheers
Awesome video. The visualization really helped me understand SWR
That is an excellent video on standing waves.
Great video! It's so nice to see things come together in reality after studying this stuff on paper.
Very nice and clear to see how it behaves
Incredible! I've been struggling to understand SWR and this helped me a lot!
I wish we had videos like these when they taught waves & antennas in college. All the test equipment were costly, we did not have time, and the teacher wasn't really interested because we could not visualize it! but it looks so cool :)
Nice Video. I clicked like and shared with some coworkers who are learning about this for FM Broadcast (Low power).
Fantastic video. Please continue making these informative videos on RF!
amazing, really helped me understand standing waves
I've been following whenever; your way and material of explaining things is it. Thank you Sir. ae.
Just saw saw this excellent video. I hope you are compensated in some way for all of your vauable videos! I have learned so much from you.
This is really awesome. Really appreciate the demo.
Well done indeed- reminds me of the old HP slotted lines we used at Solitron Microwave. 73
Great job on bringing my Emag class to life. Thank you.
A very clever demonstration
Your videos are always great. I'll be waiting for the next one !
RF black magic, utterly fascinating.
It was a shame I discovered this video today. I would have save a lot of questions.
It´s great.
Thanks
Really good demonstration!
thank you so much for these videos
you make understanding electricity sooo much easier..
you're doing amazing work
Brilliant demo!
Clever way to show VSWR, many thanks, from M3KQW. 73s
Magic explanation and demo!
Another fantastic and informative video. Keep them coming. Karl
This is a fantastic video.
Hello Alan. Thank you for your time spent making these videos.
In your summary at 10:15, if we can relate that a mis-termination of a transmission line as being an antenna that does not have a reactive, capacitance property of 50 Ohm at the frequency of operation. As well as not having our transmission line from the antenna to our SWR meter at 1/2 wave increments to the Velocity Factor of the coax, would only mean that we would not be able to truly see what are VSWR actually is.
For example, if our main run is a random length of coax and we tune an antenna to the coax with the swr meter in our shack, although the swr meter is showing a reasonable swr it doesn't mean our antenna is a 50 ohm termination. Effectively not radiating power from the antenna but the coax as well diminishing the Effective Radiated Power.
On the other hand, if we were to have our main run from the antenna to our SWR meter in increments of a 1/2 wave length at the frequency of operation to the Velocity Factor of the coax. Only then would we be able to tune our antenna to the lowest VSWR possible (or as close to 50 ohms as possible). Maximizing our Effective Radiated Power.
Make sense?
First point of clarification - there is a mis-termination if the antenna does not have a *RESISTIVE* impedance that is equal to the transmission line impedance (not a reactive or capacitive property). If the antenna presented a 50 ohm capacitive reactance, it would have a very high SWR.
The "magic" of a half-wavelength transmission line is that the impedance looking into the line will be equal to the impedance looking into the load (antenna in this case). In other words, the load impedance is replicated when the line is a multiple of half wavelengths long. A longer or shorter transmission line will result in a change in the impedance looking into the line, but does NOT change the SWR on the line. This is a very important statement to grasp - changing the line length does NOT change the SWR, it just changes the complex impedance seen looking into the line. This is illustrated pretty well in one of my videos on the smith chart (th-cam.com/video/ImNRca5ecF0/w-d-xo.html). Of course, this is assuming negligible loss in the transmission line.
So, having the transmission line be not equal to a multiple of half-wavelengths long *only* means that the input impedance does not match the antenna impedance - but the SWR is still unchanged! The SWR is a function of the antenna impedance and the transmission line's characteristic impedance, *NOT* the line length. Therefore, if you make adjustments to an antenna to minimize SWR, the result will work fine regardless of line length (as long as the transmission line is not electrically part of the antenna).
Bottom line, it is NOT necessary to have the transmission line be a multiple of 1/2 wavelength in order to get maximum radiated power (maximum power transfer to the antenna).
@@w2aew
Clarification noted!
If I am reading this correctly (Cuz I aint lernt to good) The "magic" of a 1/2 wave length coax is, that it is no longer seen by the transmitter. Poof, It disappears (not taking into account losses in the coax) Ta-da! Magic!
To my understanding, the transmitter now sees the antenna only, and if the antenna dos not have a 50 ohm impedance a Standing Wave will be educed on the line and seen by the swr meter.
You have made it clear in other videos that a 1/4 wave transmission line looks like a short.(it is also mentioned in the MFJ analyzers manual) Which means the impedance value of our transmission line does change BASED ON length of line with respects to frequency applied. so using a random length of coax while making a 1/4 wave ground plane antenna affects the tuning of the antenna, while trying to make the antenna terminate our line at 50 ohms. Making the coax electrically part of our antenna.
(an experiment that everyone can do)
If I build a 70 cm 1/4 wave ground plane antenna with a random length of coax, which works perfectly fine with minimal SWR at my house and I give it to my friend for Christmas (cuz i'm such a nice guy) and he uses his own coax, which is a different length and Velocity Factor (then what I made and tuned the antenna with) his SWRs will be totally different than mine.
Now, the stipulation to this (in my opinion) is if I give him the antenna WITH the coax (in which i'm really not that nice of a guy) that i made and tuned the antenna with originally and he needs to extend the length of the coax to get to his swr meter. He would need to make a coax jumper in increments of half wave lengths. That would mean that the coax I give him IS Electrically part of the antenna (which is now a 50 OHMs to the end of the coax not to the connection at the antenna) and the extension he needs to make will not be seen by the swr meter because it is in 1/2 wave multiples. Poof, Ta-Da, Magic !!
If I would have originally used a length of coax that was multiples of 1/2 wave lengths to the frequency of operation and velocity factor of the coax, The home brew 1/4 wave ground plane antenna, would have an impedance of 50 ohms at the connector.
(End experiment)
To to sum it up (in my opinion), 1/2 wave increments of coax is the only way to do things, when setting up a station. Unless an antenna tuner is used. Even then, the work done in the transformation of impedance by a tuner would be less if 1/2 wave increments were used to and from the tuner (the transmitter will not see the coax only the tuner and the tuner would not see the coax, just the impedance mis-match of/at the antenna) That could only be proven with a VNA in which I don't own.
Alan, I would like to make something clear. I am not trying to negate, manipulate, argue, dispute anything you are saying or showing us in your video.
I really do appreciate the work you have done and your time spent making your videos. The one thing that you have done is sparked further curiosity and ambition on working towards discovery and understanding.
I thank you for that.
@@sevenoseven8494 I'm afraid you misunderstood me! The *only* thing that the 1/2 wavelength increment gives you is a replication of the antenna impedance at the coax input. There is NO REASON to restrict yourself to this!! You can use any length you need. If the antenna is matched to the coax, all is well with any length coax. If the antenna is not matched to the coax, the input impedance to the coax won't be 50 ohms, but can still be matched at the transmitter end with a tuner, regardless of coax length. The SWR on the line in this case will be the same - regardless of the coax length. Restricting to 1/2 wavelength increments does not make the tuner's job any easier. The complex impedance looking into the coax will vary with the coax length, but the SWR is the same.
@@w2aew
I'm sure I do understand you, It seems we are standing a quarter wave apart on a smith chart looking towards the center, both trying to achieve a 50 Ohm Impedance.
1) you state,
The only thing that the 1/2 wavelength increment gives you is a replication of the antenna impedance at the coax input.
my response,
that's my point! I want to make sure that my antenna has an impedance of 50 Ohms not my coax and antenna!
2) you state,
There is NO REASON to restrict yourself to this!!
My response,
It's not a restriction, having the main run to the antenna in 1/2 wavelength increments, would not be adding the complex impedance of the random length coax to the miss-matched complex impedance of the antenna, further complicating the total complex impedance of the antenna and coax. Why make things more complex then what they should be. the antenna impedance would be the cause of the miss-match on the system creating the SWRs.
3) you state,
If the antenna is matched to the coax, all is well with any length coax.
My response,
If that's the case, I can use RG6 75 Ohm coax trough out my shack. Adjust the angle and length of the ground plane of my antenna to compensate for the impedance and affect the angle of radiation of the antenna. Rendering the antenna useless. Achieving a flat SWR.
4) you state,
If the antenna is not matched to the coax, the input impedance to the coax won't be 50 ohms, but can still be matched at the transmitter end with a tuner, regardless of coax length.
My response,
That's exactly what the purpose of doing things this way. Now I know that the antenna needs adjusting. That's it! Using a half-wave length of coax ensures that the transmitter/SWR meter see the antenna and not the coax and the antenna matches to the transmitter.
5) you state,
The SWR on the line in this case will be the same - regardless of the coax length. Restricting to 1/2 wavelength increments does not make the tuner's job any easier. The complex impedance looking into the coax will vary with the coax length, but the SWR is the same.
My response,
I quote "The only thing that the 1/2 wavelength increment gives you is a replication of the antenna impedance at the coax input." any SWRs will be caused by the impedance miss-match of the antenna. It will show a similar complex impedance miss-match value (of the antenna) on a MFJ analyzer, as if the analyzer was plugged into the bottom of the antenna with no coax or separated by one 1/2 wavelength of coax or separated by multiples of a half-wave length of coax. Intern, showing me how close the antenna is to a 50 ohm impedance. Because the coax becomes less of a factor, aside for the losses of the coax. in which we have no control of.
My point is that you’re not adding any complexity when using non 1/2 wavelength increments. When using 50 ohm coax, minimum SWR occurs when the antenna is adjusted to 50 ohms, regardless of coax length. You don’t have to use 1/2 wavelength increments to know when you’ve adjusted the antenna to 50 ohms.
Thanks Alan. Another great lesson.
I am not worthy to be given these pearls of knowledge!! Lol. Great video sir. Thanks for taking time out of your day to teach a man to fish.
Thanks for sharing your knowledge
Extremely good demo
Absolutely great!
Another very interesting video Alan. Thank you.
Brilliant video
Great demostration!
Phenomenal video, thank you so much.
Very very very very nice video. Thank you so much.
So enjoyable and clean
excellent .
great way of explanation.
Excelente video, gracias por tu conocimiento