如题，我需要一根馈线（长度20m），用在HF段。因为手里是QRP电台（10w），所以希望选择线阻尽可能低的线，以减少功率损失。查询一番后暂时有两个选择，LMR400和50-12，还请各位讲下这两个具体有什么区别。三脚架：请问各位都是用什么三脚架假设短波天线的，我目前在某宝上只找到了最高10m长的三脚架，但太贵遂放弃购买（如果各位三脚架假设的高度都不是很高，我馈线也没必要买20m长的）

小Tips：实测，50-12馈线，或者1/2馈管，非常难以弯折（掰起来的手感就像是掰空调管一样，掰直不难，但是拐弯很难）。实测，50-7馈线，也很硬，且如果是高空放下，还很难掰直（一卷送过来的，怎么拉都很难避免中间有弧度）。建议：只玩短波的话，20米长度，50-5，或者50-7已经能用了，就算上馈管，比50-7的提升也有限了。另外，如果没有感受过馈线馈管的硬度，强烈建议买点样品回来感受一下，再决定拉什么线，不要像我，~~买了40米50-7回来，发现太硬了架不起来，丢家里吃灰了。~~

50-12的馈线又粗又硬很难弯折。除非你想用在固定架设环境，比如从家里到楼顶，而且今后长时间不会变动。而且短波波段馈线上的损耗不是很大，比UV段的损耗小不少。不是追求极致效率的话不用太粗的线。

我用10米～15米长的50-3馈线，50-12太吓人了。可以看一下B站成都M哥的30米50-3馈线损耗测试的视频再考虑用啥。

10m 50-3, 20m 50-5 就可以了

20米长，用50-5线足够了，HF的损耗没那么大。

短波就上LMR400。。。真没必要，实测LMR400比50-9（还是东方货）要强很多，工作在432M上，3米插损只有0.1。而50-9的要到0.3左右了。已经把4根50-9的换成了4根LMR400了。

感谢提建议的各位，这里就不一一回复了。这里先说结论：选用LMR400线缆。上两张图，分别是Times Microwave的LMR400和亨鑫的HCAAY(Z)-50-12 (1/2) [upl-image-preview uuid=7e52733a-20c8-4def-905d-38a22e728861 url=https://storage.hamcq.cn/2025-04-29/1745928013-606035-image.png alt={TEXT?}] [upl-image-preview uuid=54009319-0d0b-43ae-a063-61adb90d5205 url=https://storage.hamcq.cn/2025-04-29/1745929694-430209-image.png alt={TEXT?}] **注：我不知道这两家对比合不合适，这只是我找到的，认为是同轴线缆里面很强的两家** 可以注意到，在20m长的线缆下，LMR400在30Mhz只有0.44db的损耗，50-12的损耗只会更低。 0.44db的损耗对于我10w的发射功率的情况下，相当于最后有9w用于发射。为什么我不选择50-12？这里快速说一下，不选择的原因就是因为太沉了，这个是真不方便来回出来进行野外架设，即便50-12的纸面参数比LMR400强为什么我不选择50-5或者50-3？同样选取亨鑫的线材参数，50-3将有1.16db的损耗，即发射功率从10w降到7w 50-5将有0.7db的损耗，即8.3w **但是：对于某宝来说，这个HCAAY-50系列线材每家的参数都不一样，没有同一的参考数据。而且我问了好几家，基本上都没有30Mhz的衰减参数。** 此外，我之前参与过QRP电台的联通（WAPC上借用BH3GEX的设备，不到20w的发射功率），深知QRP电台的不易，>!更希望喊话时能少喊两句，嗓子快报废了!< 所以还是秉着一分钱一分货，选择了LMR400 番外话：我以后有考虑加一个100w的PA（但是我还是希望使用QRP电台联通更多的人），不过100w的功率，将有10.7%，17.5%，30.6%的功率损耗在线上，我个人感觉这个不太能接受，所以还是选择了损耗最低的LMR400

拿三脚架架的天线怎么会要 20m 馈线

@"BG5ELQ"#p63251 因为不只是三脚架（准备买个10m高的）用，准备找个机会扔房顶用

三脚架的选择上，主要考虑因素：一是高度，二是最顶上一节的管径和接口情况。高度主要影响便携性、发射仰角和天线效率，需要你在其中做取舍。相对固定架设的话，7米左右的灯架，个人觉得比较合适。出去野架的话，要看车能不能装得下。管径一般情况不用太在意，除非是有连接件的商品天线对最顶上一节的管径有要求（比如JPC-7）。

Question: Regarding the selection of coax cables (LMR400 and 50-12) and tripods.

BH3HSI

As the title indicates, I need a feedline (20m long) for use in the HF band. Since I have a QRP radio (10W), I'd like to choose a line with the lowest possible impedance to minimize power loss. After some research, I currently see two options: LMR400 and 50-12. Could you please explain the specific differences between these two?
Tripod: I'm curious, what tripods are you all using for your shortwave antennas? Currently, the only ones I could find on Taobao were up to 10 meters long, but they were too expensive, so I gave up buying them (If none of your tripods are very tall, then I wouldn't need a 20-meter cable either).

BA7NNC-JOE

单纯论LMR400 和 50-12那个好，那肯定LMR400的全面指标都好过50-12，唯一就是价格也很好。看自己预算咯.

三脚架通常野架都是买灯架来撑正V或者八木，当然越高的越贵，短波天线架设通常都是越高越好。虽然我用2.8米灯架的时候也通了不少，但是无可否认，五米以上，七米以上，十米以上，高度的升高带来的天线效率的提升是明显的。总之都能玩，要想玩得好，还是得看你自己的预算荷包，我自己现在野架用得4.8米灯架加上几节延长杆+15米50-3的馈线，采取架设正V+倒V组合的方式，也玩得挺开心。

另外 HF波段，使用20米馈线的损耗并不算大，50-7的馈线已经很粗很硬很难弯折了，50-12的话布线难度不低了，还不如在天线的选择上尽量选择偶极类天线其效率高会更实际一些。

BG7KBB

A few tips:

Actual testing showed that with 50-12 conductors or 1/2 feeder, it is very difficult to bend (the feel when bending is similar to bending a refrigerator pipe; bending straight is easy, but bending is difficult).

Actual testing showed that with 50-7 strands, the cable is also quite stiff. Furthermore, if dropped from a high altitude, it's difficult to straighten (even when pulling on a roll, it's hard to avoid having a curve in the middle).

Recommendation: If you only use shortwave, a length of 20 meters, with a 50-5 or 50-7 antenna, it should already be functional. Even if you add a tuner, the improvement over a 50-7 antenna will be limited. Also, I strongly recommend buying some samples to try before deciding which antenna to purchase. Don't make the same mistake as me.~~I bought 40 meters of 50-7 wire, but it turned out to be too hard and I couldn't use it. I threw it away and let it decompose at home.~~

BD8ENX

BG7KBB 是的所以我宁愿有衰减也用的 -5

BG2EWI

The 50-12 coaxial cable is both thick and stiff, making it difficult to bend. Unless you intend to use it in a fixed installation environment, such as from your home to the top of the building, and where it will not be moved or changed in the future, then using a thicker cable is unnecessary. Furthermore, the loss in the 50-12 frequency range is not significant compared to the UV range. If you are not aiming for maximum efficiency, then there is no need to use such a thick cable.

Bg2gKg

I'm considering using 50-3 to 50-12 feed lines, which are typically 10-15 meters long. I'd like to see the video from Chengdu M on Bilibili that tests the loss of 30-meter 50-3 feed lines before making a decision.

BG5VQE

10 meters, band 50-3, and 20 meters, band 50-5 are sufficient.

BG8AMG

20 meters long; 50-5 wire should be sufficient. The loss in HF frequencies isn't that significant.

BI1NIZ

For shortwave, use LMR400... it's really not necessary. In practice, LMR400 is much better than the 50-9 (or the domestic version), especially when operating at 432 MHz; the insertion loss for a 3-meter cable is only 0.1. The 50-9 has an insertion loss of around 0.3. I've already replaced the four 50-9 cables with four LMR400 cables.

BH3HSI

Thank you to everyone who provided suggestions. I will not be responding to each one individually here. However, let me state the conclusion first: We should use LMR400 cable.
The two images shown are the LMR400 from Times Microwave and the HCAAY from Hengxin.(Z)-50-12 (1/2)

Note: I don't know if comparing these two companies is appropriate, but this is just what I found and believe are the strongest in terms of coaxial cables.

It's worth noting that, for a 20-meter cable, the LMR400 exhibits an attenuation of only 0.44 dB at 30 MHz, and this attenuation will likely be even lower at frequencies between 50 and 12 MHz.
A loss of 0.44 dB, under my 10W transmission power, equates to having 9W remaining for transmission.

Why didn't I choose the 50-12?

To summarize quickly, the reason for not choosing it is that it's too heavy. It would be very inconvenient to set up in the field, even though its paper specifications (50-12) are better than the LMR400.

Why didn't I choose the 50-5 or 50-3?

Similarly, the cable parameters of Hengxin were selected, with a loss of 1.16dB for the 50-3 cable, meaning that the transmit power decreases from 10W to 7W.
A 50-5 connection will have a 0.7dB loss, which equates to 8.3W.

However, for Alibaba, the HCAAY-50 series cables have different parameters from each manufacturer, and there is no consistent reference data. Furthermore, when I inquired with several manufacturers, none of them provided a 30MHz attenuation parameter.

Furthermore, I previously participated in QRP radio communication using a connection to the WAPC (borrowing equipment from BH3GEX with an output power of less than 20W), and I have firsthand experience of the challenges involved in operating QRP radios.I really wish I could say fewer words when speaking over the radio; my throat is getting tired.

Therefore, I still chose the LMR400, sticking to the principle of getting what you pay for.

Epilogue: I have been considering adding a 100W PA (but I still hope to use the QRP radio to connect with more people). However, with 100W of power, there would be 10.7%, 17.5%, and 30.6% power loss on the line. Personally, I don't think this is acceptable, so I chose the LMR400, which has the lowest power loss.

BG5ELQ

Why would a satellite dish mounted on a tripod require 20 meters of feed cable?

BH3HSI

BG5ELQ I'm not just planning to use it with a tripod (I'm considering buying one that's 10 meters tall), but also to find an opportunity to throw it from the roof.

Liridice

When choosing a tripod, the main factors to consider are: firstly, its height; and secondly, the diameter and interface of the uppermost section.
The height primarily affects portability, antenna tilt angle, and antenna efficiency. You need to make a trade-off between these factors. If you opt for a fixed setup, a lamp stand around 7 meters would be suitable. However, if you plan to use it while traveling, you need to consider whether your vehicle can accommodate it.
The diameter is usually not a major concern, unless there are specific requirements for the antenna's connection to the uppermost section of the tube (e.g., JPC-7).

BD7JIR

I am currently using a 4.8-meter lamp pole and a vertical antenna, but I find the lamp pole too large and heavy to carry around easily. The inverted V antenna also doesn't work in the 40-meter band.
I plan to wait for the lamp stand to break, and then try a different method. I recently saw that using a 50-3 feeder cable with a support base seemed like a better value for money.

Bg2gKg

BD7JIR I learned something new that was really impressive.
I recently bought a five-meter retractable net pole and left it at my parents' house. They already had a fixed pole, so I tried attaching the new one to it and found that using a standard V-shaped attachment was relatively easy to use. However, I thought about using a lamp stand instead, but that would have been much more cumbersome.
I have a question about the "Lingke" device. Is it difficult to operate with just one person, especially when setting up the positive pole? Also, how should I fix the bottom of the Lingke device?

BI1NIZ

[未知用户]
If you're concerned about these small insertion losses, you could investigate Open Wire Feed Lines. These can be made yourself, and their insertion loss is significantly lower than coaxial cables. For a 600-ohm open line operating at 30 MHz, the loss on a 100-meter cable is only 0.35.

BH3HSI

BI1NIZ This is a great resource! I've been studying it, and I really appreciate the new insights you provided.

BH7JUO

Two rolls of coaxial cable were tested, with the SYV50-7 having a loss of 50-7 dB, and approximately 8 RMB per meter purchased from Taobao (solid polyethylene pure copper, single layer shielding). RG8U, purchased from another vendor for around 2.5 RMB per meter, is an imported "spicy chicken" cable. Based on the loss parameters, the frequency loss is similar; however, RG8U's foam material offers a greater advantage at higher frequencies.
Foam cable uses a copper-clad aluminum core and a magnesium-aluminum outer shield, making it cost-effective and having good hardness. It also has a large bending radius and low attenuation, which makes it an ideal choice for home-based installations.

BH3HSI

BH7JUO Actually, the difference in cable quality between shortwave isn't that significant. However, currently, I still prefer to minimize line loss (a sad QRP radio operator).

BH7JUO

I've used two RG8U cables, and one had a particularly hard outer shell. It took me an entire night to work with it, and my friend told me that it was a fully flame-retardant material, which would make it more difficult to use. Before buying, it's best to ask the seller if the cable has a very hard outer shell.

BH7JUO

[未知用户] Yes, but there's not much we can do about it. The primary source of losses in the feeder cable is due to the medium itself. To minimize losses, we either use air-core cables or 300-ohm ladder cables.

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