Understanding NVIS
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- Опубліковано 8 чер 2024
- This video explains the fundamental principles of near vertical incidence skywave (NVIS) propagation, including the importance of incidence angle, frequency, and common antenna types.
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Index:
0:36 Review of skywave propagation
1:30 Skip zones
2:14 NVIS overview
3:20 Practical advantages of NVIS
4:25 Operational advantages of NVIS
5:50 NVIS disadvantages
6:33 NVIS frequencies
7:52 NVIS antenna overview
8:55 Elevation and azimuth patterns
11:12 Common NVIS antenna types
15:03 Mobile NVIS antennas
16:46 Skywave vs. Groundwave
17:41 Summary - Наука та технологія
Anyone who is seriously interested in NVIS will benefit from this introduction to the concepts covered. The information is articulated and illustrated clearly.
Thanks!
Thank you for the clean and concise information
Thanks!
I really admired the detailed presentation . thank you so much for this video .
My pleasure - thanks for the feedback!
Thanks for the clear and concise explanation of NVIS Propagation theory. The minimal effects from getting jammed is great for the army and the consistent signal quality without fading is useful for digital modes. I have made a lot of contacts on NVIS. Just remember the antenna at 30 ft height brought down to 12 ft height will need shorting to get the swr down. Feel free to make a specific 60m NVIS antenna for example so you can rapidly deploy it without worry 73s VE3IPS
This is an excellent presentation on NVIS. Well done.
Thanks, appreciate the feedback!
Once again, a great presentation, this time featuring NVIS propagation and the elements behind the theory. It is only recently that I discovered your channel and have walked away wiser from the quality of your content.
This is going to go a long way in helping me construct DIY antennas that will facilitate regional HF communications with known contacts. Shouting out to @TheTechPrepper for illuminating my interest in NVIS, and thank you for the upload!
Thanks!
Excellent presentation! I am starting to experiment with NVIS and this has been one of the most well done and informative pieces I have found. Thanks for your time and effort! 73 de KC4YDY
Excellent presentation by obvious professionals that can be understood by amateurs.
Actually, quite a few of the "professionals" that work on this (such as myself, KO4LZ) are amateur radio operators as well :)
Nice introduction!! Thanks you !
Thanks - appreciate the feedback!
Spot on presentation.
Thank you!
Thank you Paul for this refresher. 7 3 de VK4SOE.
My pleasure - thanks and 73! Paul, KO4LZ
Excellent presentation...well presented! Thanks.
Very Interesting Tutorial of basics in Propagation
I have successfully deployed 2 of these in the field. The performance is truly amazing, I am using a 1:1 and 1:9 baluns and SWR is low on several bands. I highly recommend this in mountain terrain
"Amazing" is a pretty good description of NVIS performance in mountainous areas :)
Thank you that was great !
Thanks for the feedback!
Thank you for making such a well organized set of training videos! 73 de KLØT
Thanks!
It is so interesting
Best presentation sir , thanks
Really appreciate the feedback!
Wow, thank you for a very impressive presentation on NVIS ! Are those mobile antennas made by Rohde Schwarz ?
Very important information for me. Regards from UD6AQR
Very nice. Question: In long range comms, you show refraction but in NVIS you show reflection. I assume refraction is happening because of the ionization having a gradient with most being at lower levels (?) and the wave bending toward the higher density. True? At straight up NVIS there would be no refraction, but the plasma would reradiate (true?). Of course, the NVIS antenna would also be radiating somewhat off vertical, too. Maybe that's why it's called NEAR vertical incidence skywave 🙂
Good question. When it comes to the ionosphere, it's not easy to define the difference between refraction and reflection. Both cause a charge in direction due to changes in the propagation medium. For reflection to occur, this change has to be very large (air and a solid object), whereas in refraction it's a somewhat more gradual change. Reflection also requires a large (compared to wavelength) and ideally a flat/smooth object, and the change of direction is usually specular (incident angle = reflected angle). None of these apply to the ionosphere. That said, a lot of people imprecisely talk about signals "reflecting" off the ionosphere, and I'm sometimes guilty of this as well :)
Depending on the antenna pattern, height, etc. some of the transmitted signal can (does) travel straight up. NVIS is "near" vertical incidence because a purely vertical incident signal would simply come straight back down and not be useful for communication. Purely vertical incidence is useful when making measurements of maximum usable frequency (e.g. ionosondes) but not for much else :)
Good Presentation, thanks for the video.
regards from VK3,,
Tnx es 73, Paul, KO4LZ
UA-cam algorithm why are you always trying to teach me something i learned minimum 20 years ago.
Just because the azimuth and elevation don't change much doesn't mean the polarization is the same.
It's still a linear polarized signal and subject to polarization mismatch.
Not sure I buy the harder to jam part. From a distance yes from close the jamming party can illuminate the reflective part of the ionosphere with their jamming signal.
I'd bet you have to be a ways away before you couldn't be jammed.
Even from a good distance a determined jammer could construct a properly elevated dipole to take advantage of the directionality to illuminate the sky above your station even from a couple hundred miles away.
I hadn't considered the direction finding resistance but you're right direction finding an nvis ststion would take lots of effort.
Polarization is usually not preserved once the signal is refracted from the ionosphere, so the best way to deal with (potential) polarization mismatch would be to use a pair of cross-polarized antennas such as the "turnstile" vertical dipole pair shown in the presentation.
Jamming is all about efficiency, and it's a lot harder to jam if you can't concentrate power towards the receiving antenna. Yes, you could simply radiate skywards at a high angle but this would distribute the jamming power over a wide area and thus the J/S (jamming to signal) level would also be very low.
And NVIS stations can be DF'ed - I actually hold a patent on one methodology (US11550021B2) :)
Thanks!
Good presentation. Must be careful with an inverted L antenna - modelling will show that most of the current can flow in the vertical uplead, resulting in a top-loaded vertical, with attendant low-angle radiation. Making the total wire length => 1/2 wave can help this somewhat.
Thanks, Chris. I didn't appreciate that.
Could someone tell me if in an inverted V antenna, the ends of the antenna should be how many meters from the ground? Thanks.
I have limitation wired inverted V or horizontal dipole, pls suggest any vertical hf antenna design pls.
Best of best, though at some point,it was difficult to understand but overall it was informative .want to ask ," difference between angle of radiation/signal and incidence angle. And when it refers angle ,angle from horizon or angle? with vertical?"
Incidence angle from vertical (i.e. the angle at which the signal was refracted from the ionosphere)
I sense proffesionalism
Cloud warmer? You can make the rain hard to fall if the cloud is warm or u get warm water?
Good question. I think to warm up water vapor you need energy in the low GHz range, so most HF signals probably wouldn't be able to actually warm the clouds :)
both stations need to be runnin nvis for good results isnt really true. i run nvis on 75 and out to 300 miles my sig went from a 5 to 10 over from a sloper to a nvis flattop . none of the other stations were running nvis. all info is good tho... what isnt said much is... TRY IT ... GIVE IT A GO... dont take word from anyone on bad or good.. what works for one may not work for other and backwards . basic info is good tho
Thanks for the feedback - I guess it depends on how you define "good" :) I've personally worked non-NVIS stations with a NVIS antenna and vice-versa, so it can be done, but results are better with similar (vertical) radiation patterns. Thanks again - 73, Paul, KO4LZ
I like pronouncing it "EN" VIS hahahhaha nvis sounds weird, like how people would say NVGs
I've heard "en-vihs", "nih-vihs" and plain old "N -V -I -S" Most of the people I work with pronounce it "nih-vis" and that's why I used that pronunciation in this video.