孤城浪子的地盘

Wi-Fi 2.4G 15DBi全向天线图纸

来源：http://info.awmn.net/users/images/stories/Library/Handmade/helical-helix%20antenna%202_4%20GHz%20HOWTO.htm

有空再翻译

Abstract  
The helix antenna, invented in the late fourties by John Kraus (W8JK), can  be considered as the genious ultimate simplicity as far as antenna design is  concerned. Especially for frequencies in the range 2 - 5 GHz this design is very  easy, practical, and, non critical. This contribution describes how to produce a  helix antenna for frequencies around 2.4 GHz which can be used for e.g. high  speed packet radio (S5-PSK, 1.288 Mbit/s), 2.4 GHz wavelans, and, amateur  satellite (AO40). Developments in wavelan equipment result in easy possibilities  for high speed wireless internet access using the 802.11b (aka WiFi) standard.  
  

Theory in a birds eye  view
The helix antenna can be considered as a spring with  N turns with a reflector. The circumference (C) of a  turn is approximately one wavelength (l), and, the distance  (d) between the turns is approx. 0.25C. The size of the  reflector (R) is equal to C or l, and can be a  circle or a square. The design yields circular polarization (CP), which can be  either 'right hand' or 'left hand' (RHCP or LHCP respectively), depending upon  how the helix is wound. To have maximum transfer of energy, both ends of the  link must use the same polarization, unless you use a (passive) reflector in the  radio path.
The gain (G) of the antenna, relative to an  isotrope (dBi), can be estimated by:  

G = 11.8 + 10 * log {(C/l)^2 * N *  d}  dBi                (1)  

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一般人都误以为：在线播放的音乐不占用硬盘空间
其实并不是这样

通过IE或者其他浏览器打开网页在线听的，音乐文件会被缓存到Internet临时文件目录，这个Internet临时文件目录可以在浏览器选项里设置其使用空间大小，由浏览器自动管理，当所分配的空间用完后，会自动删除最旧的数据

而QQ音乐不同，它把音乐文件缓存到
C:\Documents and Settings\Administrator\Application Data\Tencent\QQMusic\cache

没有空间分配设置！不会自动删除！

我在某一天收到系统通知：C盘磁盘空间不足
奇怪了，之前还有6G多空间，浏览器缓存、TEMP目录全清空也只是多了几百M，难道被狗吃了？

后来一个个目录的找，终于找出QQ音乐这个罪魁祸首，被偷偷霸占了5G多空间，全部删掉，搞定

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