Talk:Near vertical incidence skywave

message: — JIP | Talk 09:24, 16 October 2005 (UTC)

message: Yesterday I added this article to the "Radio frequency antenna types" category on the basis that NVIS antennas are not infrequently discussed as such in amateur contexts, but today it occurred to me that there is a distinction between the skywave itself and the antenna that makes use of it. Still, such antennas are discussed in the article, even if they are in many cases just a subset of dipoles and (aside from their distance from the groundplane) physically indistinguishable therefrom. Of course, NVIS could be employed by other types of antenna. I'm going to leave the category tag as I think NVIS might be a useful concept to have in a list of antenna types, but wanted to raise the discussion if anyone thought otherwise. --Ninly 01:56, 4 June 2007 (UTC)
thread_title: NVIS as antenna type?

message: In my opinion, it is not a new type of antenna. The significance comes from how the antenna is deployed, not built. The key is how far above the ground to deploy the dipole (7ft +/- 3 inches for the 40 meter version). Also, this article only discusses one reflector directly beneath the dipole, but other reference materials show 3 reflectors and 10db of gain, not the 6 shown here. Other articles place two more reflectors on the ground exactly parallel to the antenna but 6 feet to each side of the antenna.
I would also like to see this article referenced in the "40 meters" article as 40 meters is the highest band to benefit from NVIS and is apparently the most popular band for this propogation method.  —Preceding unsigned comment added by 68.42.4.138 (talk) 15:39, 10 October 2007 (UTC)
thread_title: Antenna configuration or propogation method, not necessarily antenna type

message: The difference between mere vertical skywave communication and NVIS is in the operational doctrine worked out to provide reliable regional communication during all ionospheric and solar conditions. Automatic Link Establishment and NVIS go together very well for tactical (and/or emergency) communication, although multiple defined calling frequencies across the usable spectrum are sufficient. Pre-arranged robust and efficient methods of accurately forwarding messages are also usually considered to be a necessity.
Remember, skywave communication (even straight-up) was used for a long time before the Germans demonstrated the value of the combined antenna/operator/messaging techniques that became known as NVIS.
For tactical communications (whether military or civilian-emergency), one of the advantages of NVIS methods is that they're very insensitive to antenna altitude.  Anything from 18 inches at 100 watts up to 20% of the operating wavelength at 20 watts is "very good", and excessive power creates a fringe-interference dead zone at the border between direct groundwave and skywave-only ranges. For most of the solar cycle, hams can operate 95% of the time by shifting between 80 meters and 40 meters as necessary. Military users will spread their chosen frequencies across the spectrum from 2 to 21 MHz or higher.
While hams often work with cut-to-resonance antennas, this is neither necessary nor necessarily a good idea for emergency NVIS systems. Professionals tend to use the same automatic antenna matching systems used for rapid ALE scanning (and indeed usually combine ALE and NVIS techniques). One reason for this is that changing ground effects (such as flooding rains) can rapidly shift the resonance point of a cut-to-length antenna. Another reason is to enable rapid redeployability. One solution available to ham budgets is to use a twinlead-fed twinlead-constructed folded dipole (either resonant or with an ATU). The maximum power useful for NVIS is 100 watts, so even TV twinlead may be used. For the tuned case, be sure that the antenna is *not* resonant on 80 meters or many tuners will have trouble matching on 40.
For the untuned case, switch between antennas resonant on 40 and on 80, or use a crossed-combined element.
Wikipedia is not a howto, and I'm stepping beyond useful background for the article itself, so I'll end it here.
75.140.243.0 (talk) 18:28, 12 November 2008 (UTC)
thread_title: NVIS refers more to a comprehensive communication paradigm, not merely antenna

message: As I have been performing field-experimentation of NVIS antennas since the early 1990's, I 
added two external links to related pages on my site at http://www.tactical-link.com .. 
The links are for "Field Deployment" and "Mobile NVIS" antennas. 
Note that the additional links include information on testing done on the amateur radio 40 meter
band (see the field-deployed NVIS external link in the article) 
Also, the reason for the low height above ground is to limit ground-wave generation so that 
received skywave signal does not suffer distortion at the receiving station which can occur
when receiving both a groundwave and skywave signal. 
Trish (talk) 07:28, 2 April 2008 (UTC)
thread_title: Additional external links added on April 2nd, 2008

message: * http://www.athensarc.org/nvis.asp is fairly detailed and fairly accurate. It is from the amateur radio perspective, so is mainly useful as background education before approaching the professional and military literature.
* http://www.gordon.army.mil/ocos/ac/articles/fiedler/dfNVIS.pdf covers history and mid-1980s problems in usage in the US Army.
* http://www.athensarc.org/fm2418m.asp is a copy of the US Army FM 24-18 Appendix M. This covers only the propagation part of NVIS.
* http://www.gordon.army.mil/ocos/ac/articles/fiedler/dfskip.pdf "Skip Zone" is a result of incorrect antenna choice and incorrect training/doctrine. 
* http://www.gordon.army.mil/ocos/ac/articles/fiedler/dfnjarng.pdf initial implementation of NVIS by the NJ ARNG.
2A4Fh56OSA (talk) 20:44, 29 December 2012 (UTC)
thread_title: More potentially useful external links

message: I have added references, more information and added some images, I've just drawn myself :)  — Preceding unsigned comment added by 2A4Fh56OSA (talk • contribs) 20:44, 29 December 2012 (UTC)
thread_title:  References and images 

message: This article fails to mention the use of NVIS in the 120, 90, 75, 60, and 49 meter bands for broadcasting regionally in the tropics. (75 and 49 meters worldwide).  This is a very common use of NIVS.  I hope to add information about this technology in the next few days. Broadcasters often use higher gain NVIS antennas than those mentioned, so I will include some info on those as well. JNRSTANLEY (talk) 20:11, 17 June 2013 (UTC)
thread_title:  Broadcast use of NVIS in the tropics 

message: I intend cleaning up the inconsistent referencing used in this article within a day or two - comments please. Roger (Dodger67) (talk) 15:59, 18 June 2013 (UTC)
thread_title:  Inconsistent referencing 

message: The section on antennas seems to imply that dipoles very close to the ground are about as good (or better) than those at .2 lambda or so. Some of the references (Hawker?) may say this, I can't access them. Yet the military sources clearly indicate that you loose up to 10 or even 15 dB when you go from about .1 down to .01. Also the statement that a single wire under the dipole can add 3-6 dB seems exaggerated, although it might be so for very low dipoles where the losses are already high. Is this also from Hawker? I found one internet article that stated that on 40 meters, 7 feet plus or minus 3 inches was optimum! Can it really be that critical? What happens when someone links to an online or printed article that is itself simply wrong? I suppose one would have to find a more authoritative article stating the opposite. I am pretty sure the vertical pattern is essentially the same from .2 lambda and down, only the losses increase, so there is no QRM or S/N ratio advantage in going lower, even though the noise and signal drop on receive. On transmit it is a dead loss. My concern is that hams might settle for a very low dipole not realizing what the extra loss was. Any comments?  JNRSTANLEY (talk) 18:08, 19 June 2013 (UTC)
thread_title:  Advantages? of using dipoles very close to the ground. 

message: The article cites 7 MHz as typical daytime and 3.5 MHz as typical nighttime NVIS frequencies. This is a somewhat misleading statement as NVIS frequencies depend strongly on the geographical location. The cited frequencies may be common for mid-latitude locations (e.g. much of the continental US), but usable frequencies are typically much lower at high latitudes (nighttime MUF may be below 2 MHz) and much higher towards the equator (nighttime MUF often above 7 MHz).  — Preceding unsigned comment added by 202.156.85.200 (talk) 15:46, 6 January 2014 (UTC)
thread_title:  NVIS frequencies depend strongly on latitude 

message: Hello fellow Wikipedians,
I have just added archive links to  on Near vertical incidence skywave. Please take a moment to review my edit. If necessary, add  after the link to keep me from modifying it. Alternatively, you can add  to keep me off the page altogether. I made the following changes:
*Added archive https://web.archive.org/20151031113702/http://www.emcomm.org/projects/nvis.htm/ to http://www.emcomm.org/projects/nvis.htm
When you have finished reviewing my changes, please set the checked parameter below to true to let others know.
Cheers.—cyberbot IITalk to my owner:Online 10:14, 14 February 2016 (UTC)
thread_title:  External links modified 

message: Full disclosure: I'm studying for US FCC Amateur Extra licensing and the topic of NVIS pointed me here.  However my high school background in physics somewhat alarms me with the picture described as how signals get "bounced" off the ionosphere - which in my books is reflection and not refraction.  Refraction requires a medium change; since the signal remains in the lower atmosphere, there is no refraction taking place, it's pure reflection from the ionosphere boundary.
I claim no expertise here but will point to http://www.qsl.net/wb5ude/nvis/ for reference to ensure accuracy of the topic at hand.  — Preceding unsigned comment added by 70.57.19.180 (talk) 06:24, 5 May 2018 (UTC)
thread_title:  Refract vs Reflect