Achieve Better Efficiency with Your HF Mobile Antenna
DXE-MM-1——让车载短波天线发挥更大效率的利器
Due to their very nature, HF mobile antennas must be physically short compared to their wavelength. In order for them to hear and radiate effectively, they must also be properly matched to the 50 ohm antenna port on your HF rig.
由于车载短波天线本身的特性，与短波的波长相比，这些天线本身必须非常短。为了能有效的接收和发射，这些天线还必须和短波设备上50欧姆天线端口正确匹配。
The impedance found at the feed point of HF mobile antennas varies all over the place. The reason for this is the variance in the mobile environment itself. The size and type of vehicle, the ground area it covers and even the space between the body and the Earth (ground) all have an affect on impedance. You may find that the best impedance match you can achieve results in is a 3:1 SWR at resonance!
在车载短波天线的馈电点发现的阻抗分布四处。原因是汽车内外环境本身的差异造成的。车辆的大小和类型、地面区域覆盖、甚至身体和地球之间的空间(接地)都对天线的阻抗产生影响。你会发现3:1 驻波比值居然是最好的阻抗匹配!
Many mobile HF antennas are naturally between 10 ohms and 36 ohms at resonance. With 10 ohms at a 50 ohm feed point the resulting SWR is 5:1! Likewise, 36 ohms yields a 1.4:1 SWR. Matching at 1.4:1 isn’t too bad, but 5:1 is definitely an issue. Fortunately, there is a convenient solution to the problem.
很多车载短波天线自然地在10欧姆和36欧姆之间的共振。10欧姆的天线在50欧姆馈点产生5:1的驻波比 ! 同样，36欧姆产生1.4:1 的驻波比。在1.4:1的匹配不是太坏，但5:1的驻波比绝对是个问题。幸运的是，现在有一个方便的解决问题的办法。
DX Engineering Dual Impedance Antenna Transformers DXE-MM-1
DX Engineering 双阻抗天线变压器 DXE-MM-1
DX Engineering MM-1 Dual Impedance Antenna Transformers are ideal for adjusting the impedance mismatch in your HF mobile! When the natural resonant impedance of the antenna is at 30 ohms or below, the MM-1 mobile unun can provide the needed match. With a 50 ohm input, it provides a 25 ohm port and a 12.5 ohm port to facilitate mobile HF matching.
DX Engineering MM-1双天线阻抗变压器适用于在移动通信时调整阻抗失配!当自然共振天线的阻抗等于或低于30欧姆时，MM-1可以提供所需的匹配。50欧姆的输入，它提供了一个25欧姆和12.5欧姆的端口来促进移动车载天线的匹配。
Let’s say that your antenna analyzer indicates an antenna impedance of 22 ohms. Your SWR without an MM-1 would be 50/22 or 2.27:1. That’s enough to cause considerable power rollback in most modern HF rigs. Using the MM-1 25 ohm port, your SWR would be 25/22, or 1.14:1. That’s a very significant improvement!
假设你的天线分析仪显示天线阻抗22欧姆。未安装MM-1的驻波比将是50/22或2.27:1。这足以引起相当大的功率反射到短波设备上。利用MM-1 25欧姆接口，驻波比将达到25/22,或1.14:1。这是一个非常显著的改善!
Many hams are using antenna analyzers to adjust mobile HF antennas. When a mismatch is indicated at resonance, a DX Engineering MM-1 unun can solve the problem!
许多火腿使用天线分析仪调整车载短波天线。在共振失配时，DX Engineering的MM-1 unun 可以解决这个问题!
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source：http://qrznow.com/achieve-better-efficiency-with-your-hf-mobile-antenna/ via DXengineering Blog
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