Why Half Wavelenght? Why Quarter Wavelength? (
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- เผยแพร่เมื่อ 30 ธ.ค. 2021
- Sam, is working on his licenses and wants to know about Wavelenghts. Do they relax over distance, do smaller wavelenghts eventually morph into full wavelengths? Watch to find out.
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This explanation made more sense to me than any of the books I have read so far. Naturally, that leads me to ask... how does the 5/8-wave antennas work?
Very informative Dave, Thanks and Happy New Year.
Thank you for the wonderful content, Dave!
Very helpful-thanks for posting.
Thank You that is the best discussion I have heard on radio waves in 45 years in the hobby. 73
THE best explanation ever. Thank you so much!
Great explanation!
Subscribed! Great knowledge
Thank you, Dave. Happy New Year. NOQFT
Nope. I could have used 10 minutes more. Happy New Year Dave. Thanks for all you do.
It's hard to convey this theory.
That's probably the best explanation I've seen on this subject.
Thanks Dave and Happy New Year to you.
David. THANKS! Dan
You explain these subjects well! Happy New Year!
@ 1:33 (initial answer) "...actually no, none of that." - epic!
Thanks Dave !
73 XE1RME
Happy New Year!
Excellent that was. Mark, 2E0MSR.
Makes good sense until I wonder how my 5/8 and 7/8 2m or triple-5/8 440 antennas work. HAHA! Good stuff, Dave!
off topic question: is analog still a thing? I recently got a SDR and everything I seem to pick up is digital. do the new radios have decoders built in or something?
Dave:
HAPPY NEW YEAR & Don't cha just love that electromagnetic propagation, behavior and principles are defined in general or in part by: Maxwell's equations, Heinrich Hertz effect, Amperes Law, Kirchhoff's law, Poynting Vectors, Abraham Lorentz force, Faraday's Law, Gauss's Law, Fresnel's equations, Babinet's equations, Planck's constants, Lienard/Wiechert's potential, Kerr effect, Einstein photoelectric effect, Summerfield / Norton propagation, Brownian motion; on and on, ad infinitum....
LOL!
73' de K4WRF
Wow, Dave is certainly out of the game, I am sure... 😀
De VU2RZA
Another great video! Thanks Dave. I have been reading that while the magnetic field is a most useful concept, it really isn't a separate field but rather a component of the electric field that comes from relativistic effects of moving charge. It also suggests that what propagates isn't a wave per se, but rather a changing wave front induced by static and moving charges in a transmitting antenna. Looked at over time as the disturbance goes past a distant antenna at the speed of light, the changing value of the electric field induces a similar shaped force in the receiving antenna. If you send a sine wave (rf), you get back a sine wave. Pretty much the only shape disturbance we can easily send and receive are sine waves since they come from and can be captured by resonant circuits.
There is an electromagnetic field; the two work as one. Waves do propagate, but they are also particles (photons at RF are enormous and this isn't a useful way to discuss the ham bands). All waves are made of sine waves combined in different ways (multiple frequencies).
Well that's a new theory you have here 🙄
De VU2RZA
Cut to the chase is a half wave antenna better than a quarter wave antenna as far as transmitting and receiving?
Vey clear and technical explanation, now, please allow me to make a question, why does a 2.4ghz wifi antenna's wave lenth active element is 50mm, since 1/2 wave lenth of this kind of antenna is about 60mm?
Following up, what is special about the 5/8WL antenna ?
About the full wave antenna, as a kid in the 80ies (remember no internet to google stuff) we know he wave length was +/- 11 meters, we (me and friends) did not have the money to buy a antenna so we used old fence wire at the fields back of out houses. The antenna was horizontal, two wires 11 meters long, so the total length 22METERS!!! I remember after tuning it a bit (shorten or stretch the antenna wire a view cm) we had nice SWR. Also our signal would go for miles whit only 0.5 Watt (our radio`s where 0.5 watt by design and FM modulated).
So the full wave dipole can work, or...? please tell me..
Dipoles are good if you have height (radiation pattern.) Vertices are good if you have width (radials)
I think about this IN CHURCH as a kid. Frequencies are like the pipe organ notes. Low frequencies are made by the big pipes in the church organ. The high frequencies are made by the little pipes. I would guess if you had pipes the exact same size sitting in the back of the church, they would vibrate when the same size pipes are played by the organ in front. And they would at half and quarter sizes, too. But the complete "full wave" pipe would work the best? 73 DE W8LV BILL
Happy New Year to everyone & ask Dave. 73 de Your Friend Uncle Guenter
does this apply to a loop antenna?
that drawing of wire fields violates the laws of Physics.
Yes its based on tglhe oscillating " dipole charges" but that only applies with*** free space*** between the charges.
.It does not happen with a conductor in between.
Dave, you always have great information. Thank you.
Is that accelerated AC current the osolation, Of the radiator, Amplified?
Still confused. 80 meter half wave is resonant on 40, 20, and 10. Those equate to full wave, double wave, and quad wave respectively. Seems like they shouldn't work, yet they work great on my EFHW, 260ft dipole. And my Diamond X700 vertical that not only works, but has incredible gain.
which is better 1/4, 1/2, or 5/8 ?
Konstantin Meyl says the waves in the near field are actually longitudinal/compressional waves. Then they collapse Into transverse about 1/6th wave length away.
What about 5/8 wave, how does that work?
Howdy.
If I understood You correctly You do not recommend full wave dipoles. Why ?
My understanding is that the radiation pattern of a full wave is like 4-leaf clover whereas that of a half wave is a 2-leaf clover. I see no practical difference.
I believe feeding a full wave is different though. If low impedance is desired feeding should be done a quarter from either end. If centre feeding is desired one needs to use a balun to step up the impedance since the centre impedance is high.
Regards.
This is very informative thanks.... Question, If I am building an antenna strictly for listening and not broadcasting. What if any advantage does a full wavelength antenna have over 1/4 and 1/2 wavelength antennas?
Mark, a full wavelength antenna would have gain over a half or quarter wavelength antenna. The problem is the feed point impedance would be very high (too high to be practical). Your 50 ohm coax would act like a resister of sorts. The big advantage with using half wave length antennas is they match perfectly with 50 ohm coax. They also don't need radials or a ground plane 9like the quarter wave) to radiate properly. They are complete antennas and a reasonable size to fit most situations. Hope this helps.
@@Mikheno I was thinking of a full length wire for shortwave listening only
@@markhadley1545 Mark, you'll have the same problem with matching the antenna to the feed line. Again, 50ohm coax would be the same as adding a resister to your full wave antenna. You could match it by attaching the coax somewhere other than the center of the wire but I don't know where that point is. You're still better off working with 1/2 wave antennas and 50 or 75 ohm coax.
@@Mikheno Interesting
@@markhadley1545 Mark, let me add that you can use a full length antenna if you feed it into a tuner first. Since your talking about SW listening you would need a manual tuner. Companies like MFJ have fairly inexpensive small tuners just for the SW crowd. The tuner would correct for any feed point impedance issues. I've used inverted "L" antennas with great results using a tuner at the feed point. Good luck.
Dave can you explain why high swr damages a radio? What is the physics behind that?
Not Dave, but I may be of help. SWR, Standing Wave Ratio, is a measure of the radio wave that was not radiated by the antenna system, returning to the transmitter. The antenna system dissipates the energy by radiating the energy into the ether or converting it to heat. What is left over reflects back to the transmitter. This in turn causes the final amplifiers to heat up, as they try and push the power they were designed to push, against not only the transmission line, but the reflected energy which is returning, as well. (excessive heat beyond the design specifications and component capabilities.) Designers account for some of this, which is why you don't have to get a perfect match. Exceeding their design limits results in damage by the amplifier 'pushing too hard', and eventually failing.
Analogy, stand in the ocean with no storm. The waves coming against you are not a problem. The energy in the waves is of little consequence. (proper swr tuning.)
Stand in the same place in the ocean, with a hurricane bearing down. The waves push you around, knock you over, etc. The energy in the waves are too much to handle. (energy return from improper swr tuning.)
Hope that helps.
Maybe a stupid question. Is quarter wavelength antenna balanced?
Generally not
So the signal doesn't just originate at the tip but the whole length of the antenna?
Yes, absolutely. The whole length radiates.
💡
😃
...FOR THE HELL OF IT-(?)
Using terms like "...things speed out..." make it difficult to understand for a beginner. "A nice point". Why is it a nice point? You explain without showing how the impedances are distributed. This would show how you can overlap the schemes and show electrically in similar manner keeping high voltages at the ends rather than confusing the issue with radiation theory rather than answering the question. You confuse me and I've been a ham for almost as long as you.
Hi, ha..ha..ha.. that's Dave.. 🙄
De VU2RZA
Daer Dave, I watch your videos over many years now and found them always very informative and educative. I have subscribed to your channel. Unfortunately, I feel that this video is one of your worst. I wouldn´t post this here but I experience that many of your recent videos show increasingly deteriorating presentation skills. You my have all the excellent engineering knowledge in your head but I wish you would prepare more on the topics. Referring to the headline this video was loaded with unneccessary and partly misleading information. F.e., you discussed the induction of a magnetic field on a piece of wire which is correct but not sufficient when talking about antennas. Here we are dealing with electromagnetic fields. I was puzzeled about your explaination of near and far fields. What has this to do regarding the question of the viewer? I´d rather you discussed the differences in propagation angles and when or why one could use these antenna designs for different deployments (DX, local comms, NVIS). Mayby additionally answering the question why antenna gain is not so crucial. And finally what about a 5/8 lambda design. How does a 5/8 come into play in comparison to 1/2 and 1/4 lamda vertical antennas? Dave, please don´t get me wrong. I don´t want to bash around but to convey a constructive feedback. Many thanks for yor work. Stay safe and healthy in 2022, Chris.
Hi, yes. You have said what I wanted to say here.
He is trying to answer but without any preparation and hence it turns out to be full of absurdity. Especially when the question is raised by an swl he should have been very careful. The way he makes use of the drawing board is pathetic and is evident that he is fully confused. Drawing the current wave pattern and the voltage wave pattern on a half wave long center fed dipole itself is hard for him. He never makes the symbol of lambda correctly. He brings in Faraday inappropriately.
Probably he wants to make more videos in a short time but without any valid content.
And as usual he fails to acknowledge the positive criticism with open mind.
In a previous comment hiis back response is really funny.
De VU2RZA.
Spelling is incorrect wavelength not waveleght