[upl-image-preview url=https://storage.hamcq.cn/2023-04-06/1680778456-397993-image.png] 这个有啥说道？这个电容到底是在哪边？会影响啥？看了不少文章没太透彻，貌似放到天线侧反而筑波调不下来了。。。放在馈线侧接收确实有变化，但也调整的空间有限问题：条件所限，拉了个19米多的长线EFHW，7/14M都还行在1.5以下，但21M到22.4了， 28基本上找不到点。。。空间以及楼/地面/树的影响，没法做到理想的EFHW四波段通吃，加个电容试着调调 [upl-image-preview url=https://storage.hamcq.cn/2023-04-06/1680778902-980532-image.png] 我也得买个防水盒。。。貌似空气的线圈据说比-43/-52的在高频段效率高，损耗小

常用的端馈天线匹配有两种，一种是带电容调谐的(就是你发的图片这种)，另一种就是更常见的使用铁氧体磁环的49:1自耦变压器。自耦变压器那种在初级加电容是为了补偿高频段的损失，电容使用固定的100pf值;你发的这种则是需要调节可变电容，让LC回路谐振到当前工作频率上。效率方面来说可变电容这种会更高，但每换一个频率就要调一遍也挺麻烦的。49:1铁氧体自耦变压器那种用起来方便太多了，所以大家也就不在乎那点损耗了。

测试了下，49:1的240-52*3，在天线端接可变电容，原本在7/14 1.5 驻波的都超过3了，其他的波段更是找不到点…失败

请问图上的那个开关是干啥的，写着平衡/同轴切换，有啥意义，请专家老师给解释解释，谢谢

Does the EFHW antenna require any adjustments?

BG1SB

What's the significance of this? Where exactly is this capacitor located? What impact does it have? I've read a lot of articles, but I haven't fully understood it. It seems that placing it on the antenna side makes tuning difficult... Placing it on the feedline side does result in some changes, but there's limited room for adjustment.
Problem: Given the limitations, I managed to get a 19-meter long EFHW antenna working, with SWRs below 1.5 at 7/14 MHz. However, at 21 MHz and 22.4 MHz, I'm essentially unable to find any signal... The effects of space, building/ground/trees make it impossible to achieve the ideal four-band EFHW antenna. Adding a capacitor and adjusting the tuning might help.

I also need to buy a waterproof enclosure... Apparently, air core inductors are said to be more efficient and have lower losses in the high frequency range compared to -43/–52.

Lynx

There are two common methods for matching antennas in a coaxial system: one uses a variable capacitor (like the one in your picture), and the other uses a more common 49:1 ferrite-core auto-transformer. The auto-transformer type uses a capacitor in series with the primary winding to compensate for losses at high frequencies, typically using a fixed 100pF value. Your example requires a variable capacitor to tune the LC circuit to resonate at the current operating frequency. While the variable capacitor approach is generally more efficient, it can be cumbersome to adjust each time you change frequencies. The 49:1 ferrite auto-transformer is much easier to use, so people don't worry too much about those losses.

BG1SB

I tested it, using a 49:1 240-52 * 3 antenna, with a variable capacitor at the antenna end. The VSWR was originally above 3 at 7/14 1.5 MHz, and I couldn't find any other frequencies… It failed.

BH1VJS

Could you please explain what the switch in the diagram does? It says "balance/coaxial switch," and I'd like to understand its function. Thank you for your expertise.

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