垂直的1/4波實際上比160m的倒L好嗎?


1

令人驚訝的是,我無法找到比較這兩個天線的更多信息。本質上,它們是相同的,只是一根電線較短,頂部裝有一根電線。有人有可用的性能數據嗎?我知道的基本知識是,垂直的1/4波將具有較小的輻射角,但是效率有何不同?1/4波實際上會不會比L波具有更差的局部性能?

這將是一項主要的支出,並且需要安裝工作,因此我想知道它的價值。甚至只是個人軼事證據。

此外,我注意到一個有趣的現象。我目前有一個70英尺的倒置L。與類似的低功率MW電站相比,由於它們的佔空比為100%,因此我可以更清楚地看到其影響。有趣的是,在良好條件下,我的信號似乎達到了較高的S水平(通過MW SDR監聽),但在惡劣條件下,它的信號要比MW站差。因此它具有較高的高點,但較低的低點。我想知道是什麼原因造成的?但是無論哪種方式,它都使我相信我不會有更好的性能,只有更高的可靠性。但是,這只是一個比較,所以可能是在噪音中:)

2

Below is the result of a NEC4.2 comparison of the radiation patterns & gains of the two configurations of radiators, with other things the same.

enter image description here


1

There should be some difference in efficiency, on the basis that the vertical portion of an inverted-L is "pure radiator", whereas the horizontal portion functions partially as a capacity hat (but not entirely — it also radiates). You can see this in the fact that an inverted-L has a lower feedpoint impedance than a quarter-wave built for the same band. However, the difference might not be much in your case.

The closest thing I can find to a direct treatment of your question is in W4RNL's Straightening out the inverted-L. On pages 15-18 of the PDF he considers an inverted-L for 80 meters of 69' total wire length (approximately a half-size version of your antenna) over modest radials and average ground. He doesn't discuss the quarter-wave vertical, but what he does do is look at three variants of the inverted-L: one with the vertical and horizontal segments both 34.5' ("balanced"), one with 23' vertical and 46' horizontal ("short"), and one with 46' vertical and 23' horizontal ("tall"). As expected there are differences in pattern, especially when the antenna is used on higher bands, but focusing just on the design band, he comes up with these numbers:

Short: -2.1dBi peak gain at 33° elevation, 31+j7 ohms Z
Balanced: -1.5dBi peak gain at 29° elevation, 40+j7 ohms Z
Tall: -1.4dBi peak gain at 26° elevation, 49+j10 ohms Z

Which suggests that the efficiency effect is definitely there, but that the "balanced" configuration has already reached a point of diminishing returns. If two-thirds vertical is only 0.1dB better than one-half vertical, then all-vertical is probably only 0.1dB better than two-thirds vertical. The radials in Cebik's model are pretty marginal, so maybe an antenna over a better radial field would benefit more from the additional height — but if you don't already have great radials, then you might find more payoff there.

All that said, if you want to lower your pattern, then additional height will do that for you.