
Chinese: 
今天要讨论的是
频域和时域。
大家好！
我是 Nick Ben，
是德科技的工程师。
欢迎收看本集“射频探秘”！
在上一期我们介绍了
什么是频谱分析仪
或信号分析仪，
以及它们可以用来
执行哪些测量。今天，我们将要深入讨论
频域和时域
之间的区别。
在此之前，我们已经简要
介绍过时域和频域的概念；
那么，它们之间到底有哪些区别呢？
频域又在哪些方面
可以提供关于信号的更多信息？
今天我就用手中的
这套装置
来为大家展示一下。我们把同一个信号分别输入示波器
和信号分析仪。它们分别可以
在时域和频域上
直观地显示电子信号。
您也许还记得，示波器是以
时间与幅度的关系，

English: 
Today we will be discussing frequency
domain versus time domain.
My name is-
What's up everyone? The name
is Nick Ben and I'm an engineer here at
Keysight and welcome to this episode of
What the RF! In the last episode we discussed what
a spectrum analyzer or signal analyzer
is and the various measurements you can
make with it. Today we'll go into more
detail about the difference between the
frequency and time domain.
Alright, so previously we had briefly
mentioned the time domain and frequency
domain but what exactly is the difference?
And what about the frequency domain
tells us more about our signal? Lucky for
us I have this set up here where I'm
sending the same signal into the oscilloscope
and the signal analyzer. The
oscilloscope and signal analyzer are
tools to visualize electrical signals in
the time and frequency domain
respectively. As you may remember, an
oscilloscope displays signals with

English: 
respect to time versus amplitude- or in
the time domain. Here we're outputting a
10 MHz signal from the oscilloscope's
waveform generator to channel one of the
oscilloscope, and visually this is how it
appears on the oscilloscope, as a
sinusoidal waveform with a period of
about 100 ns. Now if we were to
adjust the output from the waveform generator
to a 20 MHz signal, then this is
how it would look on the oscilloscope. Once again,
as a sinusoidal waveform with a period
of about 50 ns. Basically the
higher the frequency, the more waves we
see in the same span on our oscilloscope.
Now in my last video I got a question
from one of you asking what the
advantage of a signal analyzer is if
you're already own an oscilloscope with
built-in FFT. Well I'm glad you asked!
Signal analyzers have lower noise floors
this means they are much more sensitive
to frequency components and are better
at showing you low-level signals. Signal

Chinese: 
或者说
是在时域内显示信号。现在，我们从
示波器的波形发生器
向示波器通道 1 输出
一个 10 MHz 的信号，示波器上显示了
一个周期为 100 ns
的正弦波。
我们 把信号
调整为
20 MHz。
在这里，可以看到示波器的显示情况。这次
是周期为 50 ns 的
正弦波。简而言之，
频率越高，
我们在示波器同一量程内可以看到更多的波。
在上一期直播中
有人问到，
如果已经有了
内置 FFT 
的示波器，那么
信号分析仪还有什么优势呢？我很高兴听到这样的疑问！
事实上，信号分析仪的本底噪声更低。
这意味着
它们对频率分量更敏感，
因而更适合显示低电平信号。信号

English: 
analyzers also have better spurious free
dynamic range, or SFDR, than
oscilloscopes. Alright so now we have
this signal analyzer and as you may
remember signal analyzers display
signals with respect to frequency
versus amplitude, or the frequency domain.
If we were to output the same 10
MHz signal from the waveform
generator that we had seen earlier on
the oscilloscope to the analyzer, this is
how it would appear visually- just a
single peak at 10 MHz. And if we
were to adjust the output of the waveform
generator to be a 20 MHz signal,
then it would be a peak that appears at
20 MHz. So yeah, in the time domain
signals appear as sinusoidal waves and
in the frequency domain they appear as a
distinct impulses. Ok well now this begs
the question of "why the heck do we care
to use a signal analyzer?" Is it just to
show a wave as a line or something? Well,
in a perfect world we would see the

Chinese: 
分析仪还有
比示波器更出色的
无杂散动态范围（SFDR）。
好了，我们现在
来看这台信号分析仪，
您应该记得，
信号分析仪是以频率与幅度的关系，
或者说是以频域方式显示信号。
如果我们
同样
输出前面那样的
10 MHz 信号，
这次我们会看到
一个 10 MHz 的单峰信号。如果
我们把波形发生器的
输出调整为 20 MHz，
然后就会看到它的峰值为
20 MHz。由此可见，在时域中
信号显示为正弦波，
在频域中
则显示为独特的脉冲。这样
问题就来了，
“我们为什么一定要使用信号分析仪呢？”
它只不过是把波形显示为
一条线或其他什么东西吗？
然而问题是，在理想条件下

Chinese: 
我们看到的应该是正弦波，
就与我们在 10 MHz
和 20MHz 频率下
的示波器中看到的正弦波一样。但不幸的是，
这种理想条件在现实中是不存在的。针对不同的设备，
您常常
看到的是不那么完美的正弦波，
就像这个一样，
往往带有许多纹波，这就是我从
波形发生器将两个正弦波
输入到示波器之后的结果。您可以说
现实中的信号可以表示为
不同正弦波之和，而不是
不同的频率之和。假设
您正在设计一个产品，
该产品只能
在特定带宽内工作，而不能发射到其他带宽内
。那么，您就
必须确认在哪些频率上
有其他信号存在，
而这些信号会影响您想要从测试设备中得到的信号。这
就是信号分析仪的用途所在，
它们可以
帮助把不同的
正弦信号的
这种组合进行分离，并且
显示在不同的频率分量中。因此，如果您希望
您的设备在 10 MHz 频率下运行，
您就可以
看到干扰设备的所有其他频率，

English: 
sinusoidal waveform like the ones we saw
on our oscilloscope at frequencies of 10 MHz
and 20 MHz. Unfortunately
we don't live in a perfect world. When
dealing with various devices, it's often
you see a not-so-perfect sine wave with
many ripples, like this one that I've now
set up by feeding two sine waves from
the waveform generator into the
oscilloscope. You can say that a real
world signal can be represented as a sum
of different sinusoidal signals, rather
different frequencies. Now let's say
you're designing a product and your
product can only operate in a specified
bandwidth and it can't be emitting in
other bandwidths. Then you must determine
at what other frequencies do the other
signals exist that are corrupting the
signal you want from your device. And
that's where our signal analyzers come
in they help separate and display this
combination of different sinusoidal
signals into their distinct frequency
components. So that if you're expecting
your device to operate at let's say 10 MHz
you can see all the other
frequencies that are messing with your

Chinese: 
例如
这个 20 MHz 信号。一旦发现问题，
您可以使用带通滤波器
滤掉那些
多余的信号。好了，
本期内容讲解完毕。感谢收看！

English: 
device- for example this 20 MHz
signal. And once that's figured out you
can use a band pass filter to tune out
those extra annoying signals you weren't
expecting. Alright that's it for this
episode. Thank you so-
