Near Vertical Incident Scattering Antenna [复制链接]

好资料，记下来慢慢欣赏

慢慢 欣赏

已经几年了，不知道大家对这天线有何改进？天线效果实践感到如何？上来聊聊。

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已经几年了，不知道大家对这天线有何改进？天线效果实践感到如何？上来聊聊。

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是有好几年了，大家都忙着生活，先贴些别人典型的贴子活跃一下，慢慢地研究吧，别急
引自：http://www.eham.net/articles/4141


n.v.i.s. portable antenna  
by wb6byu on november 18, 2002

low horizontal wires, either dipoles or quarter wave
wires such as this, provide high-angle radiation that
gives good coverage out to several hundred miles when
operating below the "critical frequency". this is
called "near vertical incident skywave" propagation
by the military, while hams have used "short skip" for
years.

however, remember that "low" is a relative term when
describing antenna height. a dipole 1/4 wave in the
air will give high-angle radiation and have a higher
efficiency than something just a few feet above the
ground. a good rule is that the maximum heigh for an
nvis antenna in feet is the band designator in meters,
so the maximum practical height for a 40m nvis antenna
is about 40'. (above that the high angle radiation
is reduced.)

so performance should be at least as good - and quite
likely improved - if the wire is installed higher off
the ground when suitable supports are available. that
would also keep it out of the way of people. getting
the end up 12 to 15' would be a good start.

the military often installs their nvis antennas at
low heights for a reason: it minimizes the ground wave
signals radiated from it. this is important when they
want to keep their location secret because the ground
wave is easy for the enemy to df. (some antennas are
even used laying on the ground for this reason.)
but this is rarely a problem in amateur use, and the
antenna efficiency drops sharply at heights below about
0.08 wavelengths. this corresponds to about 20' on
75m and 10' on 40m. although antennas will still work
at lower heights when supports are not available, a
more efficient antenna allows for the same coverage
with less power, thereby extending battery life.

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已经几年了，不知道大家对这天线有何改进？天线效果实践感到如何？上来聊聊。

'
n.v.i.s. portable antenna  
by ky6o on december 3, 2002

i built my first nvis this past weekend, for 40m. fun stuff! in order to get it to match without a tuner, i finally had to cut (wrap, actually) 10' off *each end*. thank goodness for a digital antenna analyzer!

but the performance (receive-wise) is amazing. you really need to try it to experience it. most of the "hash" you usually hear on 40m sails right over the top of this thing. just don't plan on cross-country qso's with it, but for 300 to 500 miles, i'm sold.

my advice, however (since this is the first one ive ever built) is build a nvis dipole, don't waste your money buying one, like i did.

for $34, here's what i got:
1. a 1:1 balun. these are < $11 at most radio stores.
2. 75 feet of copper wire, with instructions to "cut each leg to 34', and solder to the balun lugs"
3. two ceramic insulators (for the ends of the wire)
4. a hunk of cotton rope.

trust me, you probably have these components already, in your junk drawer!

warning! nvis voltages can get rather high. please keep people/pets well away from the wire when it is "hot".

rich de ky6o

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昨天又有位爱好从很远的地方打来电话，询问有关无盲区天线的问题。呵呵，再把这个老话题翻出来，希望能能看到这篇文章，有所收益。
其实部队实战中，一般用架设高度低于1/8波长的天线称之为“高射天线”，天线辐射仰角基本上是8、90度，因此近距离0-200km以上可以实现无盲区覆盖。当然白天，黑夜需要选用好最低和最高可用频率。日频7兆，也频3.8兆都没有什么问题。
以前推出的这片文章，其实就是美国海军路站队天线手册中的推举的无盲区nvis天线,但是它没有给出数据，查阅了很多资料，整理把它放在了网上。如果把它看成普通的 inverted v dipole（倒v）天线也是可以的。
感觉nvist天线设计的好除了了高仰角、宽频率覆盖，架设快捷之外，与国内我们一般的应用得所谓高射天线相比，最大的优点一是双振子、一长一短、十字交叉设计，因而不仅可以实现80-10米频率的覆盖，而且实现了360度无方向、无越距覆盖，对解决应急通信无盲区和通信保密具有现实意义。
这跟我们爱好者使用的高架天线要求不同，爱好者希望通信距离越远越好，而作战部队在调动集结的通信距离内，不仅要求无盲区覆盖，而且要求信号不要传播到不希望到达的敌占区、非通信区域，以最大限度的限制信号的传播距离，以利于通信保密。

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本地ham经过两次拉距离实验，一次a、b两组直线28公里。第二次直线距离58公里。使用这种天线达到非常好的效果。非常值得大家在nvis通联时使用。

先做记号，慢慢看！

学习了，这个天线可以有~

choke 巴仑如果再靠近自动天调，效果会更好些吧。。。。。

值得学习的文章，有机会想实践一下

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本地ham经过两次拉距离实验，一次a、b两组直线28公里。第二次直线距离58公里。使用这种天线达到非常好的效果。非常值得大家在nvis通联时使用。

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把chock 巴仑移到自动天调根部，自动天调放在最高点，6米以上高度的倒v架设是个效率较高且有效的nvis天线，振子每边15米至20米都行，关键是频率！60米段不让用，频率不解决，肯定有盲区，，，，，天线再高仰角，高仰角区增益再高，无法反射回地面还是通不上，因为muf每时每刻都在变化中。

这个自动天调放在杆顶 高多少

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这个自动天调放在杆顶 高多少

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结合本地多次试验。4米高最好。效率和高仰角。
我们这属于南方海边，全天40米和80米相结合，基本一架台就可以通上。

那是南方，北方不一样。

[quote=电离层]那是南方，北方不一样。[/quote]
嗯……干旱地区架设高度要上升。具体还是要结合本地特征多试验。

这个怎样接天调 一组是接那个输出端 一组是接外壳吗

wj8787:这个怎样接天调 一组是接那个输出端 一组是接外壳吗  (2012-04-29 22:29) 

对的。就是这样接。

mark一下,正在学习中,等有机会试验一下,到时候再上报告!