第一次DIY巴伦，用的磁环是某宝购买的FT240-43，漆包线是1.2mm直径的，用了个50欧的精密电阻当假负载，两根线用热缩管并的已经很紧了，但是用NanoVNA测4-30Mhz的驻波比在1.28-6逐渐升高，烦请各位大佬帮忙分析一下原因出在了哪里呢？[upl-image-preview uuid=a85855aa-d1b7-4864-aeaf-109c6c4fa229 url=https://storage.hamcq.cn/2025-12-14/1765717346-754498-93a7d65d9278c1aed251ff66f15b1e0.jpg alt={TEXT?}] [upl-image-preview uuid=0f37a5ae-2c8f-48e4-8912-b0988eb5d8ba url=https://storage.hamcq.cn/2025-12-14/1765717347-47878-12969d9b28d19ed7ad080fd583892a4.jpg alt={TEXT?}] [upl-image-preview uuid=c55995cc-d5b6-4772-8249-9f7102f7a3c9 url=https://storage.hamcq.cn/2025-12-14/1765717347-279978-a83f3d81f3d8281fd374562c5088cdf.jpg alt={TEXT?}]

@"BG7XSS"#p90049 线头的漆已经刮了一部分了，回头焊个接头再试试

@"BI1MXY"#p90069 其实我还用1mm²的电线做了个对照组，两根线绞合一起再绕在另一个磁环上，线头留的超短，结果驻波比更大。。。

以下是个人拙见，如有错误欢迎指正：第一，磁环是不是淘宝30一个的FT240-43？我之前绕制扼流环使用咸鱼80的FT240-43，成品2m馈线绕制，驻波优秀，这周DIY端馈绕制49:1巴伦使用的是淘宝便宜的FT240-43，昨天下午测试，驻波乱跳，一下超级高一下自然谐振的，感觉像是磁环有问题。第二，绕制线圈的话要不要双绞？我看两股的话，其他HAM做49:1巴伦里都是做了双绞

@"BG5JKZ"#p90093 磁环是淘宝20多一个的FT240-43，测试的时候倒是没乱跳，一直很稳定的逐渐升高，我也怀疑过是磁环是不是有问题。。。为了验证是不是双绞和线头长的影响，我还用另一个同规格磁环+双绞过的普通电线绕了一个，驻波比更高4Mhz是1.4然后一直到8，看来应该不是这个原因。

先用这个无感电阻校准一下VNA。如果还这样，换成同轴馈线绕试试。

[upl-image-preview uuid=e99f7095-48f6-4727-a638-c7923f67f901 url=https://storage.hamcq.cn/2025-12-15/1765781831-812301-image.png alt={TEXT?}] 所以，为啥要用coax那

磁环看釉面感觉都不对…

What could be the reason for a DIY 1:1 Baron subwoofers setup with Boby High?

BA4JXV

This is my first DIY Balun, and I used an FT240-43 purchased from Taobao. The insulated wire is 1.2mm in diameter. I used a 50 Ohm precision resistor as a dummy load. The two wires connected with heat shrink tubing are very tight. However, when measuring the VSWR (Voltage Standing Wave Ratio) between 4-30 MHz using a NanoVNA, it gradually increased from 1.28 to 6. Could you please help me analyze the possible causes?

BG7XSS

Poor contact also leads to high standing wave.

BA4JXV

BG7XSS The paint on the wire ends has already been scraped off; I'll solder a connector onto it and then try again.

BI1MXY

Try shortening the cable a bit.

BA4JXV

BI1MXY Actually, I also made a control group using 1 mm² of wire. Two wires were twisted together and then wrapped around another magnetic ring. The ends of the wires were left very short, resulting in a larger standing wave...

BG5JKZ

The following are my personal opinions; please correct me if I am wrong.
First, is the toroidal inductor I bought from Taobao for ¥30 the FT240-43? I previously used an FT240-43 from Xianyu (¥80) to wind a choke coil. The finished product had excellent VSWR. This week, I wound a 49:1 balun myself using a cheap FT240-43 from Taobao. Yesterday afternoon, I tested it and found that the VSWR was erratic, sometimes very high and sometimes exhibiting natural resonance. It seems like there might be a problem with the toroidal inductor.
Second, should the loop wire be twisted pair? I see that other HAMs in 49:1 baluns use twisted pairs.

BA4JXV

BG5JKZ The FT240-43, which I have from Taobao (around 20 of them), didn't seem to malfunction during testing. It gradually and consistently increased in value, and I even suspected that the magnetic ring might be faulty...
To verify whether the length of the twisted pair and the cable head had an impact, I also wrapped a standard, twisted-pair cable around another identical magnetic ring, and measured the standing wave ratio at 4 MHz. The result was 1.4, which increased to 8 over time. This suggests that it's not likely due to this factor.

BG5JKZ

BA4JXV By the way, I forgot to mention that the capacitance of ordinary wire distribution is large: The insulation layer of the power line is thick, there is a distance between the turns, and the PVC layer acts as a dielectric, which introduces parasitic capacitance, leading to heat loss. I don't know if this affects the standing wave.

BG7MEB

BA4JXV 看你图片那个磁环并不是fair-rite真进口的，淘宝搜到这种上下面有弧度的磁环写着进口材料国内生产，fair-rite的磁环上下面应该是平的。虽然我不确定是不是这个问题，至少用正版保险些。如果不加巴伦直接测电阻的驻波咋样，排除下这个问题。我和你一样的绕制方式，用同轴线绕的，6米波段，效果很好。上面有朋友提到绕线的阻抗问题，我不太清楚原理。

BI1RRE

The magnetic ring has an irregular color.

BA4JXV

BI1RRE The reason could be the warm light from the lamp; the first image has more accurate colors.

bg4uvr

First, use this zero-offset resistor to calibrate the VNA. If that doesn't work, try using a different coaxial feedline coil.

BA4JXV

bg4uvr Okay, I've already purchased the RG402 cable and will try it out once I receive it.

BI1NIZ

So, why use coax?

BA4JXV

BI1NIZ Are you saying that the impedance of the chosen cable isn't correct? I'll try using a different feed line later to see if it makes a difference.

BG2EFX

Is it a problem with the light?
What makes me think the colors are off?

bg7jns

There are too many turns! Let's try removing half of them.

BA7KK

Regarding the 50Ω non-inductive resistor, try soldering the resistor leads directly to both ends of the insulated wire without using a connector. Additionally, you can change the method of winding with three twisted wires. When twisting the wires, use a hand drill clamp to twist the insulated wire evenly.

BA4JXV

BG7MEB Indeed, the main problem was with this resistor. Replacing it with the resistor from the VAN calibration kit resolved the issue.

BA4JXV

Thank you to all my predecessors for your helpful answers and guidance. The problem has now been resolved, with VSWR values between 6-50 MHz being below 1.1. I will organize the troubleshooting process and experimental methods later for everyone's reference.

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