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谢谢楼上指教。小环的样式有多种，不知道哪种效率最好？
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磁环天线的效率都很低。因为它的周长通常在1/4波长以下，所以实部阻抗低（通常20欧以下），而虚部阻抗高，实部阻抗高发射效率才高，虚部阻抗与近场有关，与发射效率无关。
in theorie is the performance of a magnetic loop -
0.4 db lower then a dipole or a vertical .
i have over here a homebrew trap dipole from 40-20-15-10m and the height aboveground is only 7 m(23 ft), for a good performance on 40 m the dipolemust have a height of 1/2 wave above ground ( 66ft). i don't have a radiation angle on 40 m and it's only good for contacts in europe and not good for dx, now the 1.5 m loop tuned to 7 mhz with a effiecency of 38 % (38 w erp ) and a angle radiation of about 20 degrees performs
better than the dipole because the vertical magnetic loop only 1 m above
ground as a angle radiation and the dipole don't.
another advantage is that the reception on a loop is mutch better,
on 20m i have with the dipole s5 noise from the big city, if i switch to the
loop i have s1 noise and hear stations who are buried in the noise when
