Resistance is a real physical component.抵抗是真正的物理組成部分。 Through Ohm's law we can know the relationship between voltage, current and resistance, U=I*R通過歐姆定律，我們可以知道電壓，電流和電阻之間的關係，U = I * R
We analyze the specific relationship between these three through a specific circuit, please see the simplest circuit diagram below.我們通過特定的電路來分析這三個之間的特定關係，請參見下面最簡單的電路圖。 This circuit diagram consists of only a power supply, a resistor and some wires.該電路圖僅由電源，電阻和一些導線組成。
當然，該電阻器的電阻也可以用萬用表直接測量。
The characteristic impedance is different.特性阻抗不同。 When measuring a 50 ohm characteristic impedance with a multimeter, it will be found to be a short circuit.用萬用表測量50歐姆特性阻抗時，會發現這是短路。 This requires us to conceptually distinguish resistance (even if it is exactly XNUMX ohm resistance) and characteristic impedance are two different things.這要求我們從概念上區分電阻（即使恰好是XNUMX歐姆電阻）和特徵阻抗是兩件事。 Like the degree of temperature (Celsius) and the degree of angle, it is not one thing.像溫度（攝氏度）和角度一樣，這不是一回事。
Everyone knows the physical quantity of resistance, so I won't explain it here.每個人都知道電阻的物理量，因此在此不再贅述。 Let's analyze what is the sacred characteristic impedance, and under what conditions will this thing be used.讓我們分析一下什麼是神聖的特性阻抗，以及在什麼條件下使用該特性。
實際上，特徵阻抗是與射頻緊密分離的物理量。 在了解特性阻抗之前，首先要了解射頻。 我們知道，廣播電台，手機通信信號，wifi等都是將信號能量傳輸到外部的設備。 也就是說，能量從天線射出，並且能量不返回到天線。 我出去時不會回來。
Well, after we understand the radio frequency, we will come to the specific wire that transmits radio frequency energy.好了，在了解了射頻之後，我們將介紹傳輸射頻能量的特定電線。 The RF signal transmitted on the wire is also the same.線上傳輸的RF信號也相同。 I hope that it will not be transmitted back in the past.我希望它不會過去傳播。 If there is energy back in the back, the transmission effect is poor.如果背面有能量，則傳輸效果很差。
為了更具體地解釋特性阻抗，讓我在這裡進行類比：
There are two wires on the same circuit board (assuming that they are two very long wires, you can imagine how long they are), because the same board, the copper thickness of the two wires are the same .同一塊電路板上有兩條導線（假設它們是兩條很長的導線，您可以想像它們有多長），因為同一塊板上的兩條導線的銅線厚度相同。 The length (infinite length) and thickness of the two wires are the same.兩條線的長度（無限長）和粗細相同。 The only difference is the width.唯一的區別是寬度。 Assume that the width of the 1st wire is 1 (unit) and the 2nd wire is 2 (unit).假設第一線的寬度為2（單位），第二線的寬度為1（單位）。 In other words, the width of Line XNUMX is twice that of Line XNUMX.換句話說，第XNUMX行的寬度是第XNUMX行的寬度的兩倍。
下圖詳細顯示了兩條導線的示意圖。
As shown in the figure above, if the same radio frequency emission source is connected at the same time, and the same short period of time T, then let's see what the difference between the two wires will be.如上圖所示，如果在同一時間連接相同的射頻發射源，並且在相同的短時間段T內連接，那麼讓我們看看兩條導線之間的差異是什麼。 For the same emission source, the output RF voltage of the two wires is the same, and the RF transmission distance is the same (assuming that both are the speed of light, but the actual speed is less than the speed of light).對於相同的發射源，兩條導線的輸出RF電壓相同，並且RF傳輸距離相同（假設兩者均為光速，但實際速度小於光速）。
The only difference is the line width, and the line of line 2 is twice as wide as line 1, then line 2 needs twice the power of line 1 to fill the extra line width area (actually the copper skin and bottom surface of the wire The resulting capacitive effect).唯一的區別是線寬，線2的線是線1的兩倍，然後線XNUMX需要線XNUMX的功率的兩倍來填充額外的線寬區域（實際上是銅皮和線的底面）由此產生的電容效應）。 In other words: QXNUMX = twice QXNUMX換句話說：QXNUMX =兩次QXNUMX
因為i = Q / T（RF電流=功率/時間），所以可以知道2號線的RF電流是1號線的RF電流的兩倍（因為時間相同，所以2號線的功率是1號線的功率的兩倍）。第XNUMX行）。
好吧，我們知道i2 =兩次i1
At this point, we are not far away from finding a mysterious characteristic impedance.在這一點上，我們離發現神秘的特徵阻抗並不遙遠。 Why, because we know that resistance = voltage/current.為什麼，因為我們知道電阻=電壓/電流。 In fact, the characteristic impedance also has this relationship: characteristic impedance = RF voltage/RF current.實際上，特性阻抗也具有以下關係：特性阻抗= RF電壓/ RF電流。
由上可知，RF電壓相同，電流關係為i2 = i1的兩倍
這樣，線2的特性阻抗僅為線1的一半！
這就是我們所說的線越寬，特性阻抗越小。
上面的示例說明了特性阻抗和電阻之間的差異，以及為什麼特性阻抗與同一板上的線寬相關，而與長度無關。
實際上，有許多因素會影響特性阻抗，包括材料，導線與地面之間的距離以及許多其他因素。
電線的特徵阻抗用通俗的詞語（只是一個隱喻）來描述，這是電線對在其上傳輸的射頻能量的阻礙大小。
識別傳輸線上的反射
Above we assumed that the wire is infinitely long, but the actual wire length is finite.上面我們假設導線是無限長的，但是實際的導線長度是有限的。 When the radio frequency signal reaches the end of the wire, the energy cannot be released, and it will travel back along the wire.當射頻信號到達電線末端時，能量將無法釋放，它將沿著電線返回。 Just as we shouted at the wall, the sound hit the wall and came back to produce an echo.就像我們在牆壁上大喊大叫一樣，聲音撞到了牆壁上並再次產生迴聲。 That is to say, the situation that we imagined that the radio frequency signal is transmitted but not reflected back does not exist in reality.就是說，我們想像中的射頻信號被發送但未被反射回的情況實際上不存在。
單片機的樂趣•2018-01-19 14:07•26128次讀取0
Resistance is a real physical component.抵抗是真正的物理組成部分。 Through Ohm's law we can know the relationship between voltage, current and resistance, U=I*R通過歐姆定律，我們可以知道電壓，電流和電阻之間的關係，U = I * R
We analyze the specific relationship between these three through a specific circuit, please see the simplest circuit diagram below.我們通過特定的電路來分析這三個之間的特定關係，請參見下面最簡單的電路圖。 This circuit diagram consists of only a power supply, a resistor and some wires.該電路圖僅由電源，電阻和一些導線組成。
當然，該電阻器的電阻也可以用萬用表直接測量。
The characteristic impedance is different.特性阻抗不同。 When measuring a 50 ohm characteristic impedance with a multimeter, it will be found to be a short circuit.用萬用表測量50歐姆特性阻抗時，會發現這是短路。 This requires us to conceptually distinguish between resistance (even if it is exactly XNUMX ohm resistance) and characteristic impedance are two different things.這就要求我們從概念上區分電阻（即使恰好是XNUMX歐姆電阻）和特性阻抗是兩件事。 Like the degree of temperature (Celsius) and the degree of angle, it is not one thing.像溫度（攝氏度）和角度一樣，這不是一回事。
Everyone knows the physical quantity of resistance, so I won't explain it here.每個人都知道電阻的物理量，因此在此不再贅述。 Let's analyze what is the sacred characteristic impedance, and under what conditions will this thing be used.讓我們分析一下什麼是神聖的特性阻抗，以及在什麼條件下使用該特性。
實際上，特徵阻抗是與射頻緊密分離的物理量。 在了解特性阻抗之前，首先要了解射頻。 我們知道，廣播電台，手機通信信號，wifi等都是將信號能量傳輸到外部的設備。 也就是說，能量從天線射出，並且能量不返回到天線。 我出去時不會回來。
Okay, after understanding radio frequency, we will come to the specific wire that transmits radio frequency energy.好吧，在了解了射頻之後，我們將介紹傳輸射頻能量的特定電線。 The radio frequency signal transmitted on the wire is also the same.電線上發送的射頻信號也相同。 I hope that it will not be transmitted back in the past.我希望它不會過去傳播。 If there is energy back in the back, the transmission effect is poor.如果背面有能量，則傳輸效果很差。
為了更具體地解釋特性阻抗，讓我在這裡進行類比：
There are two wires on the same circuit board (assuming that they are two very long wires, you can imagine how long they are), because the same board, the copper thickness of the two wires are the same .同一塊電路板上有兩條導線（假設它們是兩條很長的導線，您可以想像它們有多長），因為同一塊板上的兩條導線的銅線厚度相同。 The length (infinite length) and thickness of the two wires are the same.兩條線的長度（無限長）和粗細相同。 The only difference is the width.唯一的區別是寬度。 Assume that the width of the 1st wire is 1 (unit) and the 2nd wire is 2 (unit).假設第一線的寬度為2（單位），第二線的寬度為1（單位）。 In other words, the width of Line XNUMX is twice that of Line XNUMX.換句話說，第XNUMX行的寬度是第XNUMX行的寬度的兩倍。
下圖詳細顯示了兩條導線的示意圖。
詳細分析傳輸線的反射，特徵阻抗和阻抗匹配
As shown in the figure above, if the same radio frequency emission source is connected at the same time, and the same short period of time T, then let's see what the difference between these two wires will be.如上圖所示，如果同時連接相同的射頻發射源和相同的短時間段T，那麼讓我們看看這兩根線之間的區別是什麼。 For the same emission source, the output RF voltage of the two wires is the same, and the RF transmission distance is the same (assuming that they are all at the speed of light, but the actual speed is less than the speed of light).對於相同的發射源，兩條導線的輸出RF電壓相同，並且RF傳輸距離相同（假設它們都以光速移動，但實際速度小於光速） 。
The only difference is the line width, and the line of line 2 is twice as wide as line 1, then line 2 needs twice the power of line 1 to fill the extra line width area (actually the copper skin and bottom surface of the wire The resulting capacitive effect).唯一的區別是線寬，線2的線是線1的兩倍，然後線XNUMX需要線XNUMX的功率的兩倍來填充額外的線寬區域（實際上是銅皮和線的底面）由此產生的電容效應）。 In other words: QXNUMX = twice QXNUMX換句話說：QXNUMX =兩次QXNUMX
因為i = Q / T（RF電流=功率/時間），所以可以知道2號線的RF電流是1號線的RF電流的兩倍（因為時間相同，所以2號線的功率是1號線的功率的兩倍）。第XNUMX行）。
好吧，我們知道i2 =兩次i1
At this point, we are not far away from finding a mysterious characteristic impedance.在這一點上，我們離發現神秘的特徵阻抗並不遙遠。 Why, because we know that resistance = voltage/current.為什麼，因為我們知道電阻=電壓/電流。 In fact, the characteristic impedance also has this relationship: characteristic impedance = RF voltage/RF current.實際上，特性阻抗也具有以下關係：特性阻抗= RF電壓/ RF電流。
由上可知，RF電壓相同，電流關係為i2 = i1的兩倍
這樣，線2的特性阻抗僅為線1的一半！
這就是我們所說的線越寬，特性阻抗越小。
上面的示例說明了特性阻抗和電阻之間的差異，以及為什麼特性阻抗與同一板上的線寬相關，而與長度無關。
實際上，有許多因素會影響特性阻抗，包括材料，導線與底板之間的距離以及許多其他因素。
電線的特徵阻抗用通俗的詞語（只是一個隱喻）來描述，這是電線對在其上傳輸的RF能量的阻礙大小。
識別傳輸線上的反射
Above we assumed that the wire is infinitely long, but the actual wire length is finite.上面我們假設導線是無限長的，但是實際的導線長度是有限的。 When the radio frequency signal reaches the end of the wire, the energy cannot be released, and it will travel back along the wire.當射頻信號到達電線末端時，能量將無法釋放，它將沿著電線返回。 Just as we shouted at the wall, the sound hit the wall and came back to produce an echo.就像我們在牆壁上大喊大叫一樣，聲音撞到了牆壁上並再次產生迴聲。 That is to say, the situation that we imagined that the radio frequency signal is transmitted but not reflected back does not exist in reality.就是說，我們想像中的射頻信號被發送但未被反射回的情況實際上不存在。
詳細分析傳輸線的反射，特徵阻抗和阻抗匹配
如上圖所示，如果我們在線路末端連接一個電阻以消耗（或接收）線路上傳輸的RF能量。
Some people may ask, why does the resistance of the characteristic impedance of the wire do not consume energy, so it must be connected to a resistor to consume it?有人可能會問，為什麼導線的特性阻抗的電阻不消耗能量，所以必須將其連接到電阻上才能消耗能量？ In fact, the wire only transmits energy, and the wire itself does not consume energy or almost does not lose energy (somewhat like the properties of capacitance or inductance).實際上，電線僅傳輸能量，並且電線本身不消耗能量或幾乎不損失能量（有點像電容或電感的性質）。 Resistance is a component that consumes energy.電阻是消耗能量的成分。
我們發現了三種特殊情況：
When R=RO, the transmitted energy is just absorbed by the resistance R at the end, and no energy is reflected back.當R = RO時，傳輸的能量最終僅被電阻R吸收，而沒有能量反射回來。 It can be seen that this wire is wireless.可以看出，這條線是無線的。
當R =∞（開路）時，所有能量都被反射回去，線路的終點將產生髮射器電壓兩倍的電壓。
當R = 0時，端點將向後反射-1倍電源電壓。
了解阻抗匹配
阻抗匹配是指工作狀態，其中負載阻抗和激勵源的內部阻抗相互適配以獲得最大功率輸出。
阻抗匹配適用於射頻等。不適用於電源電路，否則會燃燒。
We often hear that the characteristic impedance is 50 ohms, 75 ohms and so on.我們經常聽到特性阻抗為50歐姆，50歐姆等等。 How did this 51 ohm come from?這45歐姆是怎麼來的？ Why is it XNUMX ohms instead of XNUMX ohms, or XNUMX ohms?為什麼是XNUMX歐姆而不是XNUMX歐姆或XNUMX歐姆？
This is an agreement, 50 ohms should be said to be better for general radio frequency circuit transmission.這是一個協議，對於一般的射頻電路傳輸，應該說50歐姆更好。 In other words, our wires and cables need to be 50 ohms because the circuit load is equivalent to a resistance of XNUMX ohms.換句話說，我們的電線和電纜需要為XNUMX歐姆，因為電路負載相當於XNUMX歐姆的電阻。 If you make a wire with another impedance value, it will not match the load.如果您使用其他阻抗值製作導線，則它將與負載不匹配。 The further the deviation, the worse the transmission effect will be!偏差越大，傳輸效果越差！
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