[D.I.Y. + Project Log] ลองทำ DAC + Amplifier เล่นเองดีกว่า(?) ผมเรียกมันว่า FuWa :)

[ManiacMaew]

บัดกรีเนี้ยบจริงๆ
ดูปริมาณ ตะกั่วด้านบน-ล่าง ของthroughhole ค่อนข้างสม่ำเสมอกันหมด
ด้านบัดกรีขาอะไหล่เหลือสั้นๆ +สั้นเท่ากันหมด

[MONOLAB]

บัดกรีขั้นเทพเลยอ่ะครับ ใสทุกจุด

ทำไม dac Delta Sigma ไม่ดังอ่ะครับ เห็นอยู่ soundcard creative รุ่นเก่่าๆหลายรุ่น Yamaha YF724(chip XG192) การ์ดรุ่นสีสีฟ้าอมเขียวเข้มก็ใช้ ผมเจอบ่อยด้วย ผมว่าเสียงก็ดีนะครับ แต่ output yamaha yf724 ต้องมาต้องมาตกม้าตายเพราะ ic ขยาย(TEA2025) เสียง noise เยอะมากได้แรงอย่างเดียว คุณภาพเลยตกลงมาเยอะเลย

จริงๆ Chip YMF724 ครับ XG192 นั้นมันเป็นชื่อรุ่นเฉยๆ รู้สึกที่จำได้ที่มันออกมาน่าจะมีเท่านี้
YMF-724
YMF-740
YMF-744
ไม่ค่อยเหมาะฟังเพลงเท่าไรครับส่วนใหญ่มันจะเน้นพวก Synth MIDI ซะมากกว่าเทพมาก
สมัยที่ผมใช้อยู่นิชอบมากๆครับ มันเป็น สังเคราะห์ 1MB ROM กับ SOFT 3MB
ใช้ทำเพลงอยู่ สนุกดีครับ เป็น Sound ตัวเดียวที่ทำ MIDI Vibration ในโหมด XG ได้ SoundFont ทำไม่ได้

แต่ต้องใช้ VXD Driver เท่านั้นครับ สำหรับ Windows 98/ME
พอมาถึง Win2000 XP เจอ WDM นิกากทันทีเลยเลิกใช้ Vibration เน่า Synth เน่าห่วยไปหมด

[carbon_za]

YMF724 ผมก็ใช้อยู่ครับ แต่ทำภาคเอาต์พุตให้มันใหม่ เสียงน่าฟังกว่าเดิมโขเลย เทียบกันเหมือนฟ้ากับก้นเหวเลย

[keang]

ทำไม dac Delta Sigma ไม่ดังอ่ะครับ เห็นอยู่ soundcard creative รุ่นเก่่าๆหลายรุ่น Yamaha YF724(chip XG192) การ์ดรุ่นสีสีฟ้าอมเขียวเข้มก็ใช้

ระบบSigma-DeltaหรือDelta-Sigma มีอยู่ในชิบdacเกือบทุกยี่ห้อน่ะครับ

ผมว่าน่าจะมากกว่า95%ของชิบdacที่ผลิตขายในตอนนี้ ก็ยังคงใช้ระบบนี้กันอยู่ เพียงแต่เค้าจะบอกไว้ในdatasheetหรือเปล่าเท่านั้นเอง
คาดเดาว่า เบอร์ใหม่ๆในอนาคตก็ยังคงใช้ด้วย

ADC, DACนำระบบ"Sigma-DeltaหรือDelta-Sigma"มาใช้ เพื่อปรับปรุงประสิทธิภาพเรื่อง"Signal-to-Noise Ratio"


> wikipedia : Delta-sigma modulation
The technique was first presented in the early 1960s by prof. Haruhiko Yasuda while he was student at Waseda University, Tokyo, Japan, The name Delta-Sigma comes directly from the presence of a Delta modulator and an integrator, as firstly introduced by Inose et al. in their patent application. That is, the name comes from integrating or "summing" differences, which are operations usually associated with Greek letters Sigma and Delta respectively. Both names Sigma-Delta and Delta-Sigma are frequently used.


> An Introduction to Delta Sigma Converters





> Sigma-delta techniques extend DAC resolution



> 1-bit A/D and D/A Converters



> Tutorial on Designing Delta-Sigma Modulators: Part 1
> Tutorial on Designing Delta-Sigma Modulators: Part 2

[dracoV]

...
วงจรป้องกันลำโพง เค้าเก็บงานได้เรียบร้อยดีจัง ทั้งจุดบัดกรีทั้งความสะอาด เห็นแล้ว"ทึ่ง"

http://eclipsevl.org/uploaded_content/2012/03/IMG_5349resize.jpg

http://eclipsevl.org/uploaded_content/2012/03/IMG_5351resize.jpg

ฝีมือเขาเนี๊ยบดีจริงๆ นับถือๆ

อืม...ถ้าจะทำเองให้ได้คล้ายๆอย่างนี้สงสัยคงต้องวุ่นวายหน่อย ใช้ stencil, solder paste, และเตาอบ

[dracoV]

ไม่มีไรใหม่มาupdateเท่าไหร่ ... เอา USB Isolator มาลงเพิ่มนิดละกัน
ใช้เจ้าสาย USB Isolator (DeoBlue) แล้วค่อนข้างโอเคเลย

ก็เลยว่าทำแบบ Portable ไว้พกไปไหนมาไหนได้หน่อย อุปกรณ์เหลือ กล่องเหลือ จัดการทำเป็นPCB ซะ

กัดแล้วได้หน้าตาประมาณนี้

พ่นสีซะ แล้วประกอบอุปกรณ์เข้าไปหน่อย


ไหนๆทำแล้ว เลยทำไว้แบบ2หัวซะเลย เพราะมีบางตัวใช้หัว mini-USB บางตัวใช้ USB-type B
ใช้สายเล้นเล็ก(กว่านิ้วก้อย)หน่อย



แต่... หัว mini-usb ไม่มีอ่ะ เลยด้วนอยู่ ใครพอรู้บ้างว่าร้านไหนมีขายหัว mini-usb แบบไว้เข้าสายบ้าง
รบกวนแจ้งพิกัดหน่อย (ถ้าหาไม่ได้สงสัยต้องจับเอาสายที่ไม่ได้ใช้มาผ่าตัด แต่ไม่อยากเลย )

จับใส่กล่องให้ดูหน้าตาเป็นของ กอมเมอร์เจี้ยน หน่อย

By dracov at 2012-04-12
ใช้งานได้ดีทีเดียวละ เอาใส่เป๋าไปทำงานได้ละ

[keang]

ของผมนี่ท่าทางจะอีกนานกว่าจะมีเวลาทำ

มีใครสนใจ รับช่วงตัวprototypeไปลองทำบ้าง จะได้ส่งของให้รับช่วงแทนครับ
โครงการจะได้เดินหน้า คนที่รอทำจะได้มีไรทำเล่นกันเร็วหน่อย

[tiger X-fi]

เอาไปทำขายได้มั๊ยนี่ .....

[keang]

เครดิต : Douglas C. Smith
> High Frequency Measurements Web Page



February 2000 : Measuring Capacitor Self-inductance and ESR

Figure 1. Test Circuit for Measurement of Capacitor Self-inductance and ESR


Technical Background
The parasitic parameters of a capacitor, that is its equivalent series resistance (ESR) and its inductance, affect the way the capacitor performs in circuits. Some applications are very sensitive to these parameters. For instance, a bypass capacitor used between power and ground in a digital circuit must be able to supply current quickly to nearby active devices. If it has too much inductance it will not be able to do this. Similarly, the transient response of a capacitor used to divert a current pulse due to electrostatic discharge is very important to the ability of the capacitor to do its job.

So how can the parasitic parameters of a capacitor be measured? One could certainly connect the capacitor to a network analyzer and get a very good characterization. Such an instrument can be quite expensive though. Even the less expensive capacitance measuring instruments may not be available when needed. Both instruments may not provide the information in an easily usable form. If you have a pulse generator (preferably with a 50 Ohm output impedance) and an oscilloscope, you can easily measure the transient response of a capacitor. From this data the capacitor's ESR and inductance can be determined.

First, construct the simple network shown in Figure 1 at the end of a 50 Ohm coaxial cable fed from a 50 Ohm pulse generator. A 50 Ohm resistor is used in Figure 1 to terminate the coax during the rising edge and provide a total of 100 Ohms of source impedance. The resistor shown is a 51 Ohm 1/2 watt carbon composition resistor with one lead trimmed so that the resistor just seats with the trimmed lead fully inserted into the BNC connector. It may be necessary to put a little solder bump on the resistor lead so that it stays firmly in the BNC connector. The capacitor to be tested is connected between the end of the resistor and the shell of the BNC connector. An oscilloscope is connected directly across the capacitor using leads as short as possible to connect the probe. Probes with a resistive input impedance of 500 to 1000 Ohms are recommended. Standard 10X "Hi-Z" probes often have rising edge effects that will distort the part of the waveform used for the calculations.


.... ตัดเนื้อหาส่วนของการคำนวนออก แต่ควรเข้าไปอ่านเนื้อหาทั้งหมด ....


Figure 3 below shows the initial rise from the generator. The black square indicates the vertical voltage and horizontal time scales. The open circuit voltage was a little over 4 Volts with about a 5 nanosecond risetime. The data in Figures 3 through 6 were taken with an analog scope some years ago. Figures 4 through 6 show data obtained from several leaded capacitors (as opposed to surface mount). Two traces were taken for each capacitor. The lower trace was measured at the capacitor body where the leads entered and the upper trace included the minimum amount of lead to practically connect the capacitor to a printed wiring board. The upper trace would not be needed for modern surface mount capacitors unless one wanted to model the connection inductance from the capacitor to the point of interest on a printed wiring board.

Figure 3. Input From Pulse Generator


Figure 4 shows data from a 4 uF electrolytic capacitor. The ESR offset is about 50 mV yielding an estimate of the ESR of just over one Ohm. Notice that there appears to be some oscillations on the 1/C part of the slope. This could be scope probe resonance or a resonance in the capacitor. The data was taken with a standard 10X Hi-Z probe, so the probe is suspect. I have seen capacitors with pronounced oscillation from internal resonance. If you are planning to put a large capacitor in parallel with a smaller one, especially if they are constructed from different technologies, it would a good idea to check out the impulse response of the combination using this method. It is possible for the smaller capacitor to resonate with the inductance of the larger one, causing an unexpected result.

Figure 4. 4uF Capacitor


Figure 5 shows the result for a 1 uF capacitor of the same construction as the 4 uF capacitor tested in Figure 4. Note that the inductance is similar to the 4 uF capacitor, but the ESR is slightly lower. Since an analog scope was used, the waveform was repetitive and the slight slope on the left half of the waveform was the end of the exponential fall from 5 volts. If a single pulse on a digital scope was used, the slope to the left of the Ldi/dt spike would be zero.

Figure 5. 1uF Capacitor


Figure 6 shows the result for a 1 uF radial ceramic capacitor (square case). Note the low inductance and undetectable ESR. Note also that the slope of the 1/C exponential rise is flatter indicating more capacitance than the 1 uF capacitor of Figure 5. This may be due to the fact that the electrolytic capacitor used for Figure 5 may have lower capacitance near zero voltage than at its operating voltage whereas the ceramic capacitor has a more constant capacitance with voltage. The inductance corresponding to the lower trace is estimated to be 4.4 nH.

Figure 6. 1uF Ceramic Capacitor


It is interesting to note that a 0.1 uF ceramic capacitor in the same size package as the 1 uF of Figure 6 showed a slightly higher inductance in this test setup. I believe this was due to the fact that the smaller capacitor did not fill the package and internal lead inductance caused the effect. In this case, a 1 uF capacitor was a better choice than a 0.1 uF!

One of the advantages of this test is that the output waveform is the transient response of the capacitor. The voltages developed across the capacitor in this test are directly related to what will happen in a real circuit if the current risetime from the generator is similar to what the capacitor will see in its intended application.


--------------------------------------------------------


December 2011 : Measuring the Resonant Frequencies Of Heat Sink Tines

( Your heat sink can be the source of high frequency EMC emissions! )

Figure 1. Typical Heat Sink


Abstract :
Heat sinks on ICs can be a source of emissions at high frequencies in the multi-GHz range. A method of identifying high risk frequencies by measuring the resonant frequencies of the heat sink tines is discussed.

Discussion :
Many heat sinks have tines that protrude perpendicularly from a base plate such as the one shown in Figure 1. Today's clock frequencies are so high as to be able to excite the tines as quarter wave monopoles resulting in something like an antenna farm on top of the IC, potentially radiating a clock harmonic or other source resulting in an emissions problem.

One way to measure the resonant frequency of physical structures in general and heat sink tines in particular is shown in the June 2006 Technical Tidbit, Measuring Structural Resonances on this site. Basically, one would hold a very small shielded loop at the base of one of the heat sink tines to couple energy into the tine. By measuring the reflected signal from the small shielded loop, the resonant frequency of a tine can be measured as the frequency where the reflected signal experiences a dip as the tine absorbs energy from the loop. The lowest frequency this would occur at is the frequency at which the tine is 1/4 wavelength. The method is described in detail in the June 2006 article referenced above. Figure 2 shows the method being applied to a PCB test board mounted over a copper clad board. The object in that case is to measure the resonant frequency of the LC tuned circuit composed of the capacitor formed by the PCB and copper clad board, and the inductance of the short wire between them.

Figure 2. Use of a Small Shielded Magnetic Loop to Measure PCB-Chassis Resonance


I observed a case some years ago where 4.7 GHz was leaking out of every slot and seam in the enclosure of a product. It turned out that 4.7 GHz was the third harmonic of the processor clock. When I measured the resonant frequency of the hea tsink tines, the dip in the reflection from the loop was right at 4.7 GHz indicating the tines were 1/4 wavelength monopoles, very efficient radiators, at that frequency. If the tines had been longer or shorter the emissions problem would have been reduced significantly.

Summary :
Using the simple method outlined, one can determine the resonant frequencies of the tines on a heat sink. Knowing this information in combination with information about the IC used allows an assessment of the risk of emissions problems from the heat sink.


--------------------------------------------------------


September 2011 : PCB-Chassis Ground Connections - Avoiding Pitfalls Due to Unintended System Resonances

Figure 1. PCB With Chassis Ground Connection


Abstract :
PCB to chassis ground connections are often needed in electronic equipment, but if care is not taken, the PCB and the chassis ground structure can become a hi-Q resonant circuit that may cause problems. Background information is given and techniques to avoid problems in designs are discussed.

Discussion :
Connecting PCB signal grounds to equipment chassis ground is a common feature in electronic systems although not necessarily done as shown for the experimental board in Figure 1. Problems can arise when the PCB and nearby metal, whether it is another PCB or chassis metal, form a parallel plate capacitor and the connections between them form an inductor. The combination forms a high-Q resonant circuit as illustrated in Figure 2. If this resonant circuit is tuned to a clock harmonic or other critical system frequeny, there is a risk of an EMC problem or even an operational problem for sensitive circuits. At today's frequencies, all PCBs have significant capacitance to nearby metal and all connecting wires are inductors.

Figure 2. Equivalent Circuit of PCB and Chassis Connections


Summary :
Don't take chances with your design, engineer the system resonances involving PCBs rather than letting system performance fall to chance.


--------------------------------------------------------


July 2011 : Measuring ESD Stress on a PCB
( When Conventional Measurements Don't Work )

Figure 1. Measured Current Through a Protection Device on a PCB
( Vertical Scale = 50 mA/div, Horizontal Scale = 20 ns/div )


Abstract :
Measuring voltage stress on components on a PCB under ESD conditions can be difficult as the ESD noise can inject error in the measurement. Often this error is larger than the voltage of the stress to be measured. A method of measuring voltage stress is discussed that has very high common mode rejection and low ESD induced error.

Discussion :
ESD induced error makes accurately measuring voltage stresses on a PCB difficult. In addition to high common mode noise, high amplitude time varying electric and magnetic fields can introduce error in the measurement loop formed by the voltage probe and the nodes to be measured unless this loop is kept very small. One way to accurately measure high frequency voltage stress is to replace the component that is being stressed, such as an IC, with a TVS or similar protector connected across the two nodes to be measured. In series with the protector, form a loop as small as possible to insert a current probe to measure the current through the protector.

As the ESD or other pulsed voltage stress is increased, an increase in current through the parasitic capacitance of the protector will be seen that follows the stress applied. When the breakdown voltage of the protector is reached, additional increase in current may be noted and the waveform will quickly show the current waveform as the stress is increased further for a protector that clamps to a specified value. For a protector that latches to nearly a short after turn-on, like an SCR, the current at the point of latching will be seen. Figure 1 shows the current through a protector that clamps to a specified voltage in a circuit with applied stress from a Fischer Custom Communications model TG-EFT high voltage pulser. The protector capacitance is helping form a resonant response with circuit inductance. The current waveform reaches a peak of about 80 mA.

In Figure 2, the stress is doubled and the peak current reaches about 150-160 mA, approximately increasing linearly with applied stress and keeping the same waveshape except the ringing frequency is slightly higher.

Figure 2. Measured Current Through Protection Device on a PCB at 2X Applied Stress
( Vertical Scale = 50 mA/div, Horizontal Scale = 20 ns/div )


For Figure 3, the stress is increased to 3X the value in Figure 1. Note that the waveshape is beginning to change although the peak current is about 3X of the current in Figure 1, about 230 mA.

Figure 3. Measured Current Through Protection Device on a PCB at 3X Applied Stress
( Vertical Scale = 50 mA/div, Horizontal Scale = 20 ns/div )


In Figure 4, the stress is increased to 4X the value in Figure 1. Now the waveshape is definitely changed and is beginning to look like the current waveform I expect at this point in the circuit. The peak current is now almost 300 mA.

Figure 4. Measured Current Through Protection Device on a PCB at 4X Applied Stress
( Vertical Scale = 50 mA/div, Horizontal Scale = 20 ns/div )


The stress that just begins to breakdown the protector is that of Figure 3 where the waveshape begins to change. Note that we are not trying to accurately measure the current, so some electric field response of the current probe is acceptable, we are looking for a change in the waveshape of the current as the stress increases. The current probe should be as small as possible so as to minimize the loop needed to insert it into the circuit.

The lower capacitance the protector has before breakdown, the larger the difference in amplitude and waveshape will be noted at the point of breakdown. Also, if the capacitance of the protector is much larger than the original device it replaced, the capacitance may reduce the voltage across the protector resulting in a larger applied stress being required to breakdown the protector. This will result in measurement error that will understate the stress on the original device to be measured. In general, the lower capacitance the protector has the better, but for sure it should not be much larger than the original device it replaces in the circuit.

Summary :
Using a current probe and a protector connected in place of a device on a PCB to measure voltage stress on the device is a useful way to minimize error from sources like ESD in the voltage stress measurement. The capacitance of the protector used should be minimized and be on the order of the original device capactiance. The loop formed for the current probe should be as small as possible.




--------------------------------------------------------


August 2009 : The Square Shielded Loop - Part 6, Measurements in the Time Domain Using a Comb Generator
( An unusual use for a comb generator )

Figure 1. A Shielded Loop Being Used to Sense Signal Current from a Comb Generator


Abstract :
Possible sensitivity to electric fields/capacitive pickup has been a factor in the past in selecting shielded magnetic loops over unshielded ones. Data is presented to show that in the near field, shielded loops may be required for sensing signal currents in some cases. Data presented in prior Technical Tidbits have shown the opposite to be true for other cases.

Discussion :
Figure 1 shows a shielded magnetic loop probe held near a ground plane split to sense signal current. Probe construction is shown in the cutaway view of Figure 2. A section of semi-rigid coax is shorted at it's end and then bent around and the shorted end is soldered onto the coax to make a loop. A small gap is cut in the shield to permit the loop to be sensitive to magnetic fields. In Figure 2, the shield gap can be seen at the midpoint of the rightmost side of the loop, opposite the soldered junction.

Figure 2. Construction of a Square Shielded Loop


Data was also taken using the unshielded wire loop shown in Figure 3 to compare the responses of the two magnetic loops and determine when the wire loop's electric field sensitivity becomes important.

Figure 3. A Simple Wire Loop


The signal source, shown in Figure 4, for this experiment was an AET USB Powered Comb Generator. Comb generators produce a large number of harmonics that are useful in a number of frequency domain measurements normally made using a spectrum analyzer or similar instrument. But in this case, it was used to furnish fast pulses for the experiment and measurements were made on an oscilloscope. The comb generator used has a 1.8 MHz fundamental frequency and edge rates of about 400 picoseconds.

The output of the comb generator was connected to the BNC connector in the upper left corner of the circuit board in Figure 1. The resulting current in the signal path and the load resistor on the right side of the board resulted in signal current flowing around the split in the ground plane and both shielded and unshielded loops were used to sense this current.

Figure 4. AET USB Powered USB Comb Generator


Figure 5 shows the test setup using the simple wire loop of Figure 3. This is the same setup shown in Figure 1 for the shielded loop except for the use of the unshielded loop.

Figure 5. Test setup with unshielded wire loop


Figure 6 shows the output of the shielded loop. A resonance at about one GHz can be seen on the waveform. This could be partially due to loop self resonance or capacitive coupling to the shield. To test the effects of electric field coupling, the loop was rotated by 180 degrees. The inductive pickup should invert and any capacitive pickup should stay nearly the same. The reversed loop output is shown in Figure 7 and is just an inverted version of the wave shape in Figure 6. Since the waveforms in Figure 6 and Figure 7 are inverted with otherwise the same shape, capacitive coupling to the loop is not significant for this configuration.

Figure 6. Output from shielded loop
( vertical scale = 10 mV/div, horizontal scale = 2 ns/div )


Figure 7. Output from shielded loop - reversed orientation
( vertical scale = 10 mV/div, horizontal scale = 2 ns/div )


Figures 8 and 9 show the same cases for the unshielded wire loop. One can easily see these waveforms are not just inverted versions of each other. There is significant capacitive coupling between the loop and the circuit. The capacitive coupling combined with the inductance of the wire probably produced the lower frequency resonance easily seen in Figure 9 and to a lesser extend in Figure 8.

Figure 8. Output from wire loop
( vertical scale = 10 mV/div, horizontal scale = 2 ns/div )


Figure 9. Output from wire loop - reversed orientation
(vertical scale = 10 mV/div, horizontal scale = 2 ns/div)


I encourage you to read the other five Technical Tidbits in the "Square Shielded Loop" series. These are linked just below the summary paragraph. In the September 2008 Technical Tidbit, "The Square Shielded Loop - Part 5," the unshielded wire loop was used for signal injection of pulses with a 2 ns edge rate. A significant capacitive effect was not present. If fact, for injecting signals into the board of Figure 1 over the ground split parallel to the signal path, the simple wire loop worked better than the shielded loop, having a flatter frequency response. In that case, the shield of the loop formed a parasitic resonant circuit with the circuit board that affected the frequency response of the coupling from the loop to the board.

Summary :
Significant capacitive coupling was demonstrated when using an unshielded wire loop to sense current flowing near a ground plane split. Yet, other Technical Tidbits in the "Square Shielded Loop" series show that for injecting a signal into a signal path crossing a ground break, the simple wire loop was superior. Until more work is done, one must test to see which type of loop works best for a given situation and not just assume that one type of loop is always better.


--------------------------------------------------------


April 2010 : Identifying Switching Power Supply Noise in Systems
( Frequency Domain Measurements )

Figure 1. Test Setup For Measuring Switching Power Supply Induced Noise Current into a Nearby Wire
( Spectrum Analyzer Screen at 10 dB/div Vertically and 10 MHz/div Horizontally )


Abstract :
Switched mode power supplies can generate significant harmonics of such an amplitude as to cause EMC emissions problems in the 30 to 100 MHz range and occasionally at higher frequencies. Identifying switching power supply noise is discussed as well as one coupling method that can result in excess radiated emissions.

Discussion :
Figure 1 shows the test setup used to generate the data. The setup is composed of a switching power supply, a (black) wire draped across the supply, an Agilent N9320B spectrum analyzer, and an Fischer F-33-1 current probe. The power supply is powering a 48 Watt, 12 Volt incandescent light bulb through the yellow test leads. The black wire passing through the F-33-1 current probe is about three meters long and its center has been positioned over the power supply. The plot on the analyzer screen in Figure 1 extends from zero Hz to 100 MHz at 10 MHz/div.

The noise floor on the screen of the analyzer is about 30 dBuV, a level that corresponds to enough current flowing in a one half wavelength dipole antenna to just hit the CISPR/FCC class B emissions limits in the 30 to 100 MHz frequency range. You can see the level of current near 40 MHz is about 20 dB above that level and could cause a Class B emissions problem. In reality, the power supply exhibits broad band noise, but the current in the wire peaks at the frequency at which the wire is a one half wavelength dipole. At that frequency, the driving point impedance of a dipole is near 70 Ohms, its minimum value, and the induced voltage from the power supply in the black wire is able to produce a current maximum at the center the wire.

The local field from the power supply is probably not physically large enough to radiate efficiently at 40 MHz, but once it induces enough current in the nearby black wire, the wire itself is long enough to be an efficient radiator. That is what has happened in this case.

We know that the source is the power supply for this simple case, but in some cases the source might not be so obvious. One way to discover if a broadband noise, such as shown on the analyzer screen in Figure 1, is due to a switching power supply is to adjust the analyzer as shown in Figure 2.

Figure 2. Spectrum Analyzer Screen Centered at 43.5 MHz with a 100 kHz/div Horixontal Scale and a Resolution Bandwidth of 1 kHz


The analyzer has been adjusted in Figure 2 to focus the plot around a center frequency of 43.5 MHz with a frequency span of only one MHz, 100 kHz/div. The resolution bandwidth has also been lowered from 100 kHz in Figure 1 down to one kHz, a value consistent with the horizontal scale of 100 kHz/div. With these analyzer parameters, you can clearly see peaks in Figure 2 separated by about 120 kHz, the fundamental frequency of the switching power supply used for this experiment.

Noise originating in switching power supplies that operate at a constant frequency will produce a spectrum plot similar to Figure 2, although the spacing of the harmonics may be different. That the noise is actually coming from a specific supply can be determined by holding a small loop probe near the power supply to pick up induced noise. Display the loop output on an oscilloscope or spectrum analyzer to determine the fundamental frequency. If the observed noise has a harmonic spacing the same as the fundamental switching frequency of the power supply, the supply is the likely source of the noise unless there are other supplies in the system with "the same" fundamental frequency. For the case where there are several power supplies with "the same" fundamental frequency, they are likely slightly different and this information can be used to narrow the source of the noise down to one supply out of several.

Summary :
By expanding the spectrum plot of a broadband noise, individual harmonics from the source of the noise can be resolved. In many cases, the spacing of harmonics on the expanded plot will identify a switching power supply as the source of the noise.

[IcsakamaTo]

อลังการงานสร้างครับ แหล่งรวบรวมผู้มีวิทยายุทธ....แต่หลัง ๆจะออก Hi-end ละ

[dracoV]

^^ ไม่ถึง hi-end หรอกครับ 555+
ออกแบบ+DIY ธรรมดาๆประสาอยากเล่นน่ะครับ

[dracoV]

เข้ามาปัดฝุ่น ทำความสะอาดบ้านซะหน่อย
ยังไม่มีไรอัพเดทมากนัก ช่วงก่อนชีพจรลงเท้า ไปนู่นมานี่ไม่ค่อยว่างเลย

และก็ร้อนมั่กๆ อยู่บ้านเปิดแอร์ตลอด บัดกรีไรไม่ได้อีก บ้านที่กทม. ไม่ได้ซื้อเครื่อง purifier ควันตะกั่วมาติดไว้ใช้

[poh1998]

[MONOLAB]

ช่วงนี้ก็หยุดพัก DIY เครื่องเสียงอยู่เหมือนกันครับ
มาทำเครื่องจักรอยู่กำลัง DIY USB MINI CNC ไว้เดินกัด PCB เล็กๆเล่นๆดู
ขี้เกียจใช้ไข่ปลาทำแล้ว - -'' อากาศช่วงนี้ร้อนมาก

[dracoV]

^^ ดีครับ น่าสนใจนะ ผมก็เคยคิดจะทำอยู่เหมือนกัน DIY CNC แต่ไม่มีเวลามาออกแบบ+ทดสอบปรับปรุง
และขี้เกียจทำ firmware แต่มันก็มีชุดcontrol สำเร็จขายอยู่เหมือนกัน
ไปๆมาๆ ร่ำๆจะซื้อ ชุดเล็กที่มีขายๆกันอยู่

เผื่อ ยังไงทำเสร็จอะไรเสร็จเอาโปรเจคมาเผยแพร่นิด เผื่อลอกการบ้านครับ