Why are trapezoidal balanced feeder cables, which are commonly used abroad, less common in China?

antimonysin

为什么国外ham比较常用的（至少arrl天线手册里很多）梯形平衡馈线国内没什么卖的呢？
（还是我关键词用错了？）

BG2MCU-BY2026SWL

antimonysin In China, finished balanced feed lines are almost non-existent, while they are very expensive abroad.
The demand for domestic ham racks often cannot use balanced feed lines. Balanced feed lines require a distance of at least half a meter from surrounding objects, and dust on top will affect the loss of the line, making them very sensitive. Coaxial cables are much more practical; they can be installed easily.
A balanced line has a special advantage: its loss is extremely low. However, it requires a 4:1 balun or a coax cable with a balanced line interface at the end to perform impedance conversion/matching.
Balanced feedlines are commonly used in some large loop antennas, as well as various types of dipole antennas. They can be a valuable tool for QRP enthusiasts, as they allow for maximum power to be delivered to the antenna while minimizing losses.

Liridice

Coaxial cables have relatively low installation requirements. As long as the outer sheath of the feeder does not participate in transmission, length and arrangement have little impact on resonance points and antenna efficiency. Most domestic amateur radio enthusiasts live in apartment buildings and do not have large houses or backyards.

BA7NNC-JOE

The advantage of this antenna seems to be its very high efficiency. However, the setup and adjustment can be slightly complicated, especially regarding matching the antenna to the environment. I tried it with a friend once, but we couldn't get it working properly after half a day. The small antenna tuner also didn't seem to work well, and we couldn't achieve resonance. So, we gave up.

In contrast, direct-to-chip (DTC) is simpler, or horizontal DP is even easier.

antimonysin

BA7NNC-JOE It's a feed line, not an antenna.

Ethan

Finished products are expensive; wouldn't it be better to make them yourself?

antimonysin

Ethan That's unlikely, right? A coaxial cable uses two distinct conductors connected by a coaxial jacket. Is it possible for that to be more technologically advanced than a coaxial cable?

BH9DWE

antimonysin The technical expertise was lacking, and I feel that the main reason why (hypothetically) expensive materials are used is due to the high material costs and a small market. Also, it's easy to make them yourself, so no one wants to mass-produce them.

Ethan

antimonysin I remember that there were only a few sellers on eBay, and they were all located in the UK, and the prices were quite high.🤣

BA7NNC-JOE

antimonysin Yes, it's a stepped attenuator cable, typically in the range of 300-600 ohms, not a standard 50-ohm coaxial attenuator. Stepped attenuators have high impedance and are balanced inputs, so you need to use a step-up transformer (or a separate step-up transformer + 1:1 balun) to match the impedance!

antimonysin

Ethan Okay, then it definitely falls under core technology.😂

BG6UFA

As a child, it was very common to see coaxial cables running from the roof to connect outdoor antennas.

Currently, it seems that coaxial cables are more common and offer a better balance of cost and performance compared to this type.

Hangying

Not a flat TV cable costing €300.

antimonysin

Hangying No, it's a 450 euro feed line.

bg5iyz

Personal understanding: From the perspective of the formula, the main advantage of a balanced transmission line is its inherent high impedance, which balances energy transfer at low loss in the HF range. The input impedance on both the antenna and radio side is related to the electrical length of the transmission line, and the electrical length is related to the wavelength. Since the resonant antenna itself has varying impedance outside the resonant frequency, it must be used in conjunction with a matching network and balun, except for the entire feed designed for fixed resonance. At this point, the balanced transmission line can actually be seen as part of the antenna or matching network. However, the balanced transmission line requires that the impedance is equal throughout the line, which is essential for achieving balance. In general, it is not ideal to manufacture and use in environments where the length is short, and it is very similar to coaxial cable. Furthermore, it can only be used on balanced antennas. This makes it no more convenient than using coaxial cable.

BH5HIE

https://www.dxengineering.com/parts/dxe-ll450
https://www.dxengineering.com/parts/dxe-ll300
It's a great buy, but most domestic ham enthusiasts are more interested in making money quietly than promoting their products online. Also, this device consumes a lot of power, and its performance isn't as good as expected. Therefore, those who understand it will either build it themselves or purchase one. Those who don't know how to use it can simply use coaxial cables.

antimonysin

BH5HIE By the way, how much are the shipping costs for this?~~Is shipping included?~~

BH5HIE

antimonysin When buying other items, it's a good idea to bring some along, otherwise the shipping and customs fees will be around $60-$70, plus there are high import duties on US products.

BH5HIE

BG2MCU-BY2026SWL Yes, QRP kite flying uses a balanced feed line, which works perfectly.

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