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Talk:Near vertical incidence skywave

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This is an old revision of this page, as edited by 75.140.243.0 (talk) at 18:55, 12 November 2008 (→‎Additional external links added on April 2nd, 2008). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

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— JIP | Talk 09:24, 16 October 2005 (UTC)[reply]

The two articles recently deleted from this entry were not spam. I checked them quite thoroughly and found useful HF NVIS antenna design and construction information, historical info regarding use of mobile NVIS antennas during wartime, and no mention of anything commercial whatsoever. The publication mentioned is a non-commercial ham radio magazine, as far as I can tell.

The articles should be restored. Scott Johnson 13:23, 24 April 2007 (UTC)[reply]

NVIS as antenna type?

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)[reply]

Antenna configuration or propogation method, not necessarily antenna type

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)[reply]

NVIS refers more to a comprehensive communication paradigm, not merely antenna

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)[reply]


Additional external links added on April 2nd, 2008

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)Patricia Gibbons wa6ube@arrl.net 66.245.150.200 (talk) 06:55, 2 April 2008 (UTC)Patricia Gibbons wa6ube@arrl.net66.245.150.200 (talk) 06:55, 2 April 2008 (UTC)[reply]

More potentially useful external links

75.140.243.0 (talk) 18:55, 12 November 2008 (UTC)[reply]

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