看到八木天线有几种情况 1、辐射单元有的是折合振子，有的是偶极振子。这两种振子具体有什么区别？ 2、馈电盒、巴伦是不是必须的？ 3、有的八木图纸，引向单元，一根比一根短，单元数越多，最顶端的振子越短。有的八木图纸，引向单元全部是一样长的。在实际使用过程中，这两种有什么区别？ 4、尺寸图中的间距，是振子中心点的距离，还是振子边缘的距离？如振子直径6mm，两根引向单元的间距是138mm，这138mm包含6mm（两根振子中心距离）吗？题外我用2.8mm的铁丝，按计算器435mhz尺寸做了9单元八木，天分测试，中心频点在426左右，剪短辐射单元，按比例剪短引向单元，让天线中心频点在435mhz。而此时的尺寸，如果用计算器来反向印证，频率应该是在456左右来。这个差别，是振子直径导致的，还是别的什么原因？我是馈线直接焊接到辐射单元的两根铁丝上，没有用巴伦、馈电盒。实际使用中，八木指向中继台，接收-70dbm，新名770h-85dbm，八木多1格信号的样子。这是否正常？请了解的ham指点一下。谢谢

分享一下我学到的信息，欢迎大家指正交流： 1.折合阵子的自然谐振下阻抗在300欧姆左右，偶极阵子则在50欧姆（理论好像是75欧姆）。 2.馈电和巴伦，我的理解是为了进一步降低驻波提高效率。并不是必须的。 3.引向单元变短的设计增益高、频带窄，一样长主要是为了制作简单。 4.中心间距。 5.差别的主要来源应该是你的馈线连接阵子的方式：最好馈线尽可能的直接连接到阵子，不要有引出的导线（如图）。 6.信号强度这个可能要结合你到中继台的距离来分析了，感觉太近的话可能差异会比较小，尝试一下更远的中继，我用三单元八木能打到140km以外的中继（有回波，没通联过）[upl-image-preview uuid=f13ee666-cd1b-4bc7-9019-67f4ca6b5232 url=https://storage.hamcq.cn/2024-12-30/1735572289-616963-img-7522.jpg alt={TEXT?}]

@"bd4unw"#p48103 好的，谢谢！我这有个200公里的高海拔中继，有回波单打不开语音。说明信号强度衰减到阈值以下来。

What are the differences between different types of Yagi antennas?

tudoubocai

I have observed several situations related to Yagi antennas.
1. Some radiation units are based on oscillators, while others are based on dipole oscillators. What are the specific differences between these two types of oscillators?
2、Are the power box and barrel mandatory?
3. Some Yagi antenna diagrams have elements that point towards the unit, with one element being shorter than the others. The more units there are, the shorter the top-most element becomes. Other Yagi antenna diagrams have all the elements pointing towards the unit and of equal length. What are the differences between these two types in practical use?
4. In the dimensions chart, does the spacing refer to the distance between the centers of the oscillators, or the distance between the edges of the oscillators? For example, if an oscillator has a diameter of 6mm and the spacing between the two connecting units is 138mm, does this 138mm include the 6mm (the distance between the centers of the two oscillators)?

Off-topic
I built a 9-element Yagi antenna using 2.8mm iron wire, calculated based on the dimensions of 435MHz. The center frequency test showed that the center frequency was around 426MHz. I shortened the radiating elements proportionally and adjusted the length of the driven elements to bring the center frequency closer to 435MHz. Based on these dimensions, if recalculated, the expected frequency should be around 456MHz.
What is the cause of this difference? Is it due to the diameter of the oscillator, or something else?
I connected the two wires directly to the radiating element, without using a balun or feedhorn. In practice, when aiming at the repeater with the Yagi antenna, I receive -70dBm from the repeater and 770kHz-85dBm from the New Name repeater. The Yagi appears to have one more signal level than the New Name repeater. Is this normal?

Please, Ham, could you provide some clarification? Thank you.

bd4unw

I'd like to share some of the information I've learned. Please feel free to correct me and provide feedback.
1. The natural resonant impedance of the array, when converted to a single equivalent impedance, is approximately 300 ohms, while that of the dipole array is approximately 50 ohms (theoretically, it's 75 ohms).
2. Ferrite and Balun: My understanding is that these are used to further reduce standing wave and improve efficiency. However, they are not strictly necessary.
3. The design with shorter unit lengths provides higher gain and a narrower bandwidth, primarily for ease of manufacturing.
4. Center-to-center spacing.
5. The main source of differences should be the way you connect your feed lines to the antenna array: Ideally, the feed lines should be directly connected to the array, without any extended wires (as shown in the example).
6. The signal strength may depend on the distance to the repeater. If it's too close, the difference might be small. Try using a more distant repeater. I was able to reach a repeater over 140km away with a 3-element Yagi antenna (with some echo, but not full communication).

tudoubocai

bd4unw Okay, thank you! I have a repeater that's about 200 kilometers away at high altitude. It's not transmitting or receiving voice properly; the signal strength seems to be below the threshold.

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