In lab and workshop the most commonly used signal checks an instrument is electronic oscillograph. The person's thinking is more sensitive to time concept, produce connection with time domain incident all the time, but signal often appears with frequency form, observe with oscillograph signal of the simplest amplitude modulation carrier wave is no-go also, often show to appearance of not clear modulation visits when carrier wave, what obtain on screen is 3 spectral line, namely carrier frequency and the modulation frequency that control in carrier frequency. Modulation pattern is mixedder, electronic oscillograph shows harder, the expressive capability of spectrum analyzer is strong, spectrum analyzer is the delegate of the frequency domain instrument of be worthy of the name. The number of one frequency expresses communication time the method is Fourier commutation, it discloses time signal into sine and the overlay of cosine curve, the signal that finish changes the course of frequency region by time-domain. Inchoate spectrum analyzer is receiver of a sweep essentially, input signal and signal of this locality oscillation are after first detector frequency conversion, through a group of shunt-wound different centers the belt of frequency connects filter, make input signal to show axis of filter definitive frequency is connected to go up in a group of belts. Apparent, because take a filter to be formed by passive component, spectrum appears very cumbersome on analyzer whole, and frequency resolution is not high. Since Fourier commutation can disclose input signal into the frequency heft of schism, can have the action with similar filter likewise, circuit of fast Fourier commutation replaces have the aid of low connect filter, make of spectrum analyzer form simplify, resolution heighten, measure time to shorten, sweep limits expands, this is the advantage of contemporary spectrum analyzer. Vector signal analyzer is to be in book frequency limits inside measure circuit gain and corresponding instrument automatically, the sweep frequency cause that it has interior or controllable are exterior signal source. Its function is the gain that surveys pair of circuit be measuringed that input this sweep signal and phasic, its circuit structure and spectrum analyzer are consequently similar. Spectrum analyzer needs to measure the sealed input frequency with random, vector signal analyzer measures oneself only or controlled foregone frequency; The extent that spectrum analyzer measures input signal only (scalar quantity instrument) , the extent that vector signal analyzer measures input signal and phasic (vector instrument) . This shows, the circuit structure of vector signal analyzer is more complex than spectrum analyzer, price is higher also. Contemporary vector signal analyzer also uses fast Fourier commutation, word of the following introduction people similarities and differences. The circuit of spectrum analyzer and the spectrum analyzer with FFT spectrum traditional analyzer is adjustable inside certain bandwidth the receiver of humorous, after inputting the frequency conversion below signal classics by low connect colander output, filter wave output serves as perpendicular heft, frequency regards a level as heft, on oscillograph screen draw gives coordinate to pursue, input the spectrum of signal to pursue namely. Because transducer can achieve very wide frequency, for example 30HZ-30GHZ, cooperate with exterior first detector, can expand 100GHz above, spectrum analyzer is frequency enclothes the widest measurement one of instruments. No matter measure successive signal or modulation signal, spectrum analyzer is very ideal measurement tool. But, traditional spectrum analyzer also has apparent weakness. Above all, it is only comfortable at measuring stable state signal, unsuited survey transient state event; The 2nd, it can measure the extent of frequency only, lack phasic information, belong to scalar quantity instrument accordingly and not be vector instrument; The 3rd, it needs a variety of small frequency band to connect filter, acquisition measurement should spend longer time as a result, because this is regarded as,be not real time instrument. Since can disclose the signal that be measured the frequency heft of schism through Fourier operation, achieve as similar as traditional spectrum analyzer result, appear be based on fast Fourier to alternate (FFT) spectrum analyzer. This kind of new-style spectrum analyzer uses digital method direct by imitate / digital converter (ADC) to inputting signal sampling, pursue via spectrum is being obtained to distributing after FFT is handled again. Accordingly knowable, analyzer of this kind of spectrum also calls analyzer of real time spectrum, its frequency limits is collected the limitation of rate and FFT operation speed by ADC. To obtain good instrument degree of linearity and high resolution, the ADC that undertakes counting occupying collection to signal needs 12 - 16 resolution, press sampling principle knowable, the sampling rate of ADC is equal to input signal the least double of highest frequency, the analyzer of real time spectrum that i.e. frequency upper limit is 100MHz needs ADC to have the sampling rate of 200MS/S. The ADC that at present semiconductor technology level can make composition differentiate lead 8 to lead 4GS/S with sampling or the ADC that resolution leads 800MS/S 12 times with sampling, i.e. , the instrument on the principle can achieve the bandwidth of 2GHz, right now perpendicular resolution has 8 only (256 class) , apparent 8 resolution are too low, accordingly, analyzer of real time spectrum applies to the frequency under 400MHz bandwidth paragraph, have 12 right now (4096 class) the resolution of above. For patulous frequency upper limit, next transducer can increase in ADC front, ben Zhencai uses the oscillator that direct figure job becomes, the spectrum analyzer of this kind of Composite suits to be in the frequency under a few GHz paragraph use. The function of FFT comes with sampling check the number and sampling rate token, the sampling that uses 100KS/S for example leads pair of input signal sampling 1024 a little bit, frequency of highest input is 50KHz and resolution it is 50Hz. If sampling check the number is 2048 a little bit, criterion resolution raises 25Hz. From this knowable, complete sampling of be decided by of highest input frequency is led, resolution depends on sampling check the number. FFT operation time and sampling check the number concern into logarithm, when spectrum analyzer needs high frequency rate, high resolution and high speed operation, want to choose high-speed FFT hardware, corresponding perhaps digital signal processor (DSP) chip. For example, operation time of 1024 bits of 10MHz input frequency 80 μ S, and operation time of 1024 bits of 10KHz turns into 64ms, operation time of 1024 bits of 1KHz increases to 640ms. When operation time exceeds 200ms, the reaction of screen slows, unwell the observation at the eye, help is to reduce sampling check the number, make operation time is reduced to 200ms the following. Vector network analyzer is measured to spectrum analysis and electromagnetism interference for, spectrum analyzer is the equipment that communication measures instrument middling to use, the dynamic limits that because have,is more than 100dB, under - the frequency limits of above of the bandwidth of the noise of 110dBc/Hz, 1Hz-100Hz, 50GHz, can receive extremely faint signal and resolution to give two extent to differ very big signal. The defect of spectrum analyzer is the amplitude that can show frequency weight only, and what cannot obtain signal is phasic. To certain communication yuan parts of an apparatus and communication link, amplitude and phasic must can measure at the same time come out, former be like amplifier and oscillator, latter is generation the mobile to the 3rd generation. Ever alluded in front, be based on the frequency limits of the spectrum analyzer of FFT to expand, next transducer can increase in front. Same principle can measure signal analyzer with Yu Shi, it is the union of traditional spectrum analyzer and FFT analyzer, obtain thereby in high frequency the FFT that falls with radio frequency frequency analyses ability, show extent and phasic information at the same time. The digital modulation to contemporary communication is analysed, and amplitude modulation / frequency modulation / the demodulation of phase modulation is very significant step. The frequency conversion front of spectrum analyzer expands the instrument arrives the frequency of GHz paragraph, via the input after frequency conversion signal frequency becomes comfortable the frequency that handles at FFT paragraph, the filter of the filter in circuit and spectrum analyzer is different, the filter here is not alternative, and the signal that prevents ADC to alternate the process arises is mixed fold, the false signal that appears in commutation process namely. The output of ADC divides two, obtain mix in phase orthogonal signal, classics DSP makes time the range that spectrum wins by indication screen after the FFT operation of one frequency and phasic. The frequency limits of the vector signal analyzer that at present instrument company supplies can amount to 3GHz, measuring an object is complex mobile commonly used frequency paragraph modulation signal, the base band character that is like GSM, CDMA and carrier wave are characteristic. The measurement of vector signal analyzer mode has: Demodulation of scalar quantity, vector, number and door accuse to measure. Spark can input signal by base band or adjust by intermediate frequency signal, include to spark report is gentle and phasic. Sweep means has sheet second and successive, to measuring data but for many times average, use virtual value (RMS) , peak value maintains and exponential coordinate is indicated. The main character of a kind of new-style vector signal analyzer is: Frequency limits - DC- - 2. Bandwidth of 7GHz; base band- - 36MHz; of bandwidth of 40MHz; intermediate frequency leads resolution- - 0.
001HZ; time base accuracy- - 0.
2ppm/ year; Phasic noise- - 97dBc/Hz (100Hz of carrier wave deflection) , - 122dBc/Hz (1khz of carrier wave deflection) extent limits - 45-+20dBm; Range accuracy- - losing 2dB; 3 rank intermodulation is lack fidelity---70dB. Using a field is frequency of satellite communications, enlarge jumps frequency communication, dot arrives bit of communication, and frequency monitoring and search. Divide site with the code of mobile (CDMA) for, use the analytic software of form a complete set, can obtain: The change that the power of power of average carrier wave of catapult follows time is phasic the modulation precision close quarters that compares pseudo-random noise alignment with power of channel of frequency error vicinity sends spectrum of unripe emissive frequency to measure measure with weaveform in wireless base the product of station or mobile telephone is developed, vector signal analyzer can press a variety of industry standards, the catapult that waits to GSM, CDMA and mobile phone undertake strict precision and dynamic limits are measured. In the communication product production such as CDMA, use only be being measured continuously is insufficient, use digital modulation signal to be able to measure an output conveniently power and lack fidelity wait for important parameter. Vector signal analyzer adopts Windows platform, personal computer is received to have data processing and trade outside be being passed easily, windows platform facilitating function upgrades and use other project to design a tool, the graphical interface that be familiar with can shorten study time, more time undertake put apart measure and use all sorts of designs and test tool. The spectrum of digital memory oscillograph measures digital memory oscillograph (DSO) front is ADC commutation, have spectrum to analyse ability likewise consequently, the FFT module that passes standard or choose and buy obtains spectrum to analyse character. Should point out, DSO main characteristic is time domain is measured, the product of bandwidth 100MHz has the perpendicular resolution of 10 above, the product of bandwidth 500MHz has 8 resolution only, i.e. is in 12 under spectrum analyzer on resolution - 16. The preamplifier of DSO and attenuator introduce transient state lack fidelity, the chart wave noise that is low n is behaved easily on spectrum graph. Especially high frequency number is in memory oscillograph, it is used hand in folded ADC to raise sampling rate, for example the sampling rate of every ADC is 1Gs/s, two overlay rise the sampling rate that achieves 2Gs/s. This is the simple idea that raises effective bandwidth, but when with Yu Pin chart shows, the degree of linearity of each ADC, gain, frequency is answered and sampling times have a difference a bit, can hand in in sampling clock pulse spectrum introduces in folding sampling process lack fidelity, many the sampling pulse of a group of Fs/N, fs is basic sampling frequency here, n is to make folded ADC number. Oneself of this kind of circuit arises mix fold signal to be eliminated not easily with filter, when measuring high frequency signal with DSO, want to be in what appear on spectrum graph very carefully to mix fold information. For example, when the DSO that uses two afore-mentioned sampling to lead 1Gs/s ADC to form will observe 100MHz sine wave, can be in 900, false signal appears near 1100MHz. This shows, DSO observes time domain signal is best instrument, because false signal often appears after frequency domain commutation, when measuring spectrum character, must notice " eliminate the false and retain the true " . The frequency range of analyzer of brief summary spectrum is the widest, sensitivity is tall, very comfortable distributing at the frequency of communication equipment and link measure, defect is the amplitude that can obtain input signal only. Limits of frequency of vector signal analyzer is inferior, the characteristic that uses FFT can be obtained at the same time extent and phasic, particularly the first, 2, 3 acting mobile, include the measurement of beehive, GSM and CDMA equipment. CNC Milling
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