Solving the Mystery of a Shorter Antenna - End Effect & Velocity Factor
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- Опубликовано: 7 мар 2023
- Are you wondering why your antenna is shorter than it should be? In this video, we'll explore the concepts of end effect, velocity factor, and height above ground and how these affect the electrical length of an antenna.
First, we'll explain how end-effect shortens the electrical length of your antenna and how it can be compensated by adjusting the length of the radiator. We'll also discuss how velocity factor affects the propagation speed of electromagnetic waves and how it can vary depending on the type of coating or material.
Then, we'll dive into why height above ground affects the tune of an antenna.
Whether you're a beginner or an experienced ham radio operator, this video will provide valuable insights why adjustiung your antenna can be slightlly "weird" sometimes! Stay tuned and let's dive into the world of antennas!
Callum.
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Interesting, so when an antenna element is folded back on itself it has the effect of increasing the impedance in that section, why? Because the current flow in the folded back section is in the same direction and phase as the main dipole. Therefore as the current in both sections are in phase with each other the antenna radiation pattern is unaltered. But there is now is an impedance increase in this new folded section deduced from the fact that the power in the folded section has to remain the same, but as current flow is evenly shared between the two sections, the current in each conductor is now a half of the antenna current. Then because the power remains the same in the folded section the impedance has to be raised by a factor of four to retain a balance in the equation Power = I^2 x R
So, the end-effect reduces impedance at the end of the antenna and folding back a short section increases the impedance to redress the imbalance.
Wow. Perfect!
@@DXCommanderHQ should try an inverted egg beater antenna for 40&20 meter bands it should give a lower take off angle
Easily the most informative ham radio channel on RUclips offering the best critical bits nobody else covers.
Thanks!
That certainly helps explain why, with my homebrew fan dipole, I had to keep trimming & folding back the ends of my 80m wires WAY more than I thought just to get it resonant. I'm low to the ground - 10' in the center & 6' at the ends. Makes sense now. Thanks Callum & keep up the good work!
73 K5MWA
This is why I love your movies. Because you show great knowledge, great effort, and you are endlessly entertaining. And at the end ,you explain everything in such a way that after watching it everything is clear to me. You are not homosapiens but HAMosapiens. Thank you.
Wow, thank you!
I found this really interesting and useful...people tend to know roughly, bits and pieces but you put it all together in one understandable piece. Cheers Cal! 👍😃
Awesome, thank you!
All good stuff Callum....I can understand now why I don't sleep at night......I only get chance to watch your video in the late evenings because of my work and end up going to bed trying to design a good dipole and trying to remember your calculations, great stuff, Alan (G7WBB)
HAHA! That's the spirit! :)
"The end effect only happens once." THIS. When I set up my attic 20m long EFHW I was puzzled that the overtone resonances (20m, 15m, 10m) were all higher in frequency than the fundamental (40m). Now I understand why! Thanks! (Also, I love your antenna modelling videos!)
Yes, fascinating, isn't it!
Hi Cal, it makes a lot more sense after a few cans of Stella. It is always good to eventually find out the real reason why something works, years ago we all did stuff that we knew worked but didn't really know why, love it keep up the good work.
Regards
Dave. 😀
Yes, exactly - took me about 4-years to work this one out.
Great video, back to basic, no big mathematics, just one experience with antennas, this kind of self-made knowledge ( by trying things in the real world ) goes a long way.
Well said!
Fascinating video, thanks! I've often wondered why a 40 meter antenna is recommended to be anywhere between 61' and 66'. This likely explains it, and why I had to cut so much off my roof mounted 'stealth' antenna which was only about 15' off the ground.
Interesting!
Now I understand why SWR variations occurs when I use my EFHW using an avocado tree as natural tower at home of my in laws, thanks for the explanation Cal! 73s TI2GBB -Greg.
Interesting!
Excellent explanation! I love the illustrations!
Thank you! Cheers!
Nicely done as always Cal! Thanks for sharing!
Thanks again!
Thanks for the wisdom...I have learned more from you in such a short amount of time. It would have taken I don't even know a long time otherwise... Appreciate it❤️
Me too! LOL
Yet another cracking insight on how the wiggles behave. Cheers for this C and some good info in the comments too, to help us out.
Glad to help!
It is what it is, never worried abt it just adjusted for it
Thank you again for your explanation and experience
My pleasure!
You could have told me your antenna runs in PFM and I’d believe you. I’ve been using the classic exclusively for 8 months now. Absolutely amazing.
You do a great job with all your research and experimentation. Keep it up!
Thanks for sharing!
Some great information. Thanks!
My pleasure!
Good theory for the dipole that is the exception to hight
Fantastic explanation. Thank you!
Yeah, it only took me a few years to work that out!
Makes perfect sense. Thanks for this!
Very welcome!
interesting stuff Callum, explains some of the measuremnents etc that I have experienced over the years. so another great vid cheers...Also very generous of you to share your knowledge with us all... Dave KPZ.
Nice info to know!
Thanks for watching!
It still apears to be all smoke and mirrors... Good explanation though.
Excellent as always Callum. 73 de G2ML
Woo-Hoo!
very interesting video Cal
Much appreciated
A bit much before my coffee 😅. Appreciate these videos, Cal. They help me better understand what is going on with antennas 👍
Haha.. Yes - that one - and a coffee first thing - might be too much! :)
very interesting
Great stuff Callum thanks for all you do de W9US
My pleasure!
Genius you 💪🏻
Those interactions are a ‘dark art’ to me. I’m glad you’ve got a handle on them 🧐
You like to build crazy antennas. So can you turn an 80/40(30)20/15/12/10M endfed antenna, vertical without cutting the antenna in sections? Love to see that modeled.
Cool idea!
Fascinating Cal, really interesting that! Mark, 2E0MSR
Many thanks!
Hey Cal - Love your antenna enthusiasm! I notice the music equipment in your studio and wonder if you might also be into FM radio? If so, could you possible make some videos for us 75 ohm guys that want to listen to that station that's just out of reach for the average inside dipole? I've been watching your channel for a while now and been making my own FM antennas over the years and I bet you have some great ideas to try. PS: You 50 ohm guys have all the cool hardware. Everything for 75 ohms is crap and there is no Baluns to take a 100 ohm loop to 75.
I see.. Well I'm not into FM really however I did have a 3-element yagi up once. That worked well.
PS - I just play.. Here's last week's rehearsal.. ruclips.net/video/wXCYz4A1lnI/видео.html
Thank you very much for all the useful stuff you share at your channel, 73 Yannis SV1FJK.
Many thanks!
This is really interesting and some great stuff in the comments too. I watched a bunch of the next video about testing the short 40/20 and have to ask, would the short antennas work in a parasitic array with those loading coils?
Yes!
Simple hight is might! If you have a short antenna does not
Matter how powerful it is or we’ll built if it does not clear most obstacles. That is why hand helds get there antenna replaced from those little rubber duckies that are typically less then 10 inches. If your have an extended antenna say 51 inches and you stand in a semi clear area it give just enough hight to pass the curve of the earth and low obstacles to increase your range from less then a mile to maybe 2-3 miles. Simple or what he said it the ham exam way! Thank you
Good information for the newbie Ham! If this video would have been created last year I would have abandoned the idea of an OCF dipole from the start. Further explanation: My Yaesu doesn't have a tuner. OCF dipoles are affected by end effect more than any other antenna. At 40m, both high voltage ends of the waveform contact the ends of the wire, so needs to be 3 feet short for resonance. At 20m, the center of the waveform (at the center of the wire) is a high voltage point, but not a wire end, so end effect is 50%. At 10m, you have 4 current humps, but only two find the end of the wire, so it wants to be mostly full length. 10m resonance was about 30mhz. Switched to a fan dipole, at least until I get a tuner....
Ah!!
Everything effects everything in HF!
I would include the coax and fittings/adapters in that statement. Does the length of the coax make a difference? It doesn't seem to effect SWR so much as it effects the projection of your wavelength. Just as a ground plane gives a backing for the signal to push off of, doesn't the coax do the same?
Great video, I was wondering roughly how many meters is your equipment from your antennas? Is the length negligible in the performance of your equipment?
Hello Davic.. The run from the coax feed box to the field coax box (underground) is 42m (130 ft). I use EcoFlex 15 coax for that. The between the box in the shack to the gear is about 5m (20 ft) and between the field box and the main antenna is another 12m (40 ft). So I have to use very high-end coax.
@DXCommander so do you have an external tuner or is the transceiver tuner more than adequate?
(sorry for late reply on this) Although I have a tuner, I never use it. I like antennas that just work..
Hey Cal, have you tried an S fold in the middle of the antenna wire, I saw it some where in someones design, not sure if that would so similar?
OK, I have considered this and for LONG Z or S folds, we might be experiencing too much loss.. I really don't know.
Just to be sure. This folded wire is behaving as coil not capacitor? Generally your construction is brilliant and easy to build. Another great video. All the best. SP6MI
Well, it's supplying loading, so I have no idea to be honest.. I'm at the edge of my understanding.
@@DXCommanderHQ In theory coil should lengthen the antenna to expected 1/4 lambda, what makes resonance goes down. So yes probably you are right. Physical length is fixed to be resonant as 3rd harmonics on 15m band, and coil extends that element to be resonant on 40m band.
Thanks for another interesting and educational video. Jack K5FIT
Thanks again!
Same idea as coax velocity factor., slowing effect, interesting hard line coax has a similar vf as a wire antenne, air does not slow like a foam., the foamier the coax has more air less vf, incidentally vf in coax gets lossier at frequency
👍👍👍
Great video I have been fine tuning my DX Cammander Classic after replacing the pole. The 40M is one I was working with and this video explained exactly what is happening. I love my DX Cammander it will bust a pileup.Thank You for your content it has helped me more than you know. K5OTH
Thanks for sharing
Alot of guy ask the same question… why is my antenna shorter 😂
very interesting i used to work for a tv cable co. at first we used to skin rg6 up to 412 or 500 cable with utility knives so you would score the center pin which was copper coated the bigger stuff we had coring tools. after a while they supplied us a proper tool for rg 6 cable so it wouldn't score the copper coating on the center pin because the rf flows on the the outside of the center pin was interesting did this for a few years they were a cheap company more interested in raising the price per month than fixing picture quality finalley bought out by a bigger company who ran fiber every ware problem solved
This is really about an antenna 😂
I hope so else I'm in the wrong job!
@@DXCommanderHQ like a surgeon...👌
you lost me at “WHY”
Thank you. N0QFT