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102

Actually, it is all about the waves. Even when dealing with DC, it is all managed by the electrical and magnetic fields and waves. The "fundamental laws" aren't breaking down. The rules you have learned are simplifications that deliver accurate answers under certain conditions - you haven't yet learned the fundamental laws. You are about to learn the ...

54

You are completely right. The "closed loop" rule comes from a simplification that we often use in circuit analysis called the "lumped component model". This model provides a good approximation to actual circuit behavior at DC and low frequencies, where the effects of parasitic inductance, capacitance and the speed of light can be ignored. However, these ...

45

Skin Depth The human body does have a "skin effect" but it's not as thin as you might think. Electric currents are confined to the outside of a conducting body, but humans are not very conductive, so the fields penetrate quite deep. The best example that comes to mind is 2.45 GHz - we all know that a microwave oven cooks about 2 or 3 cm into a piece of ...

35

Magnetrons are cheap, reliable, pretty efficient (65% or so- and they tolerate high temperatures so heat sinking is easy) and made with mature technology. They are also reasonably tolerant of VSWR issues (if the user does not put a proper load in the oven, for example). They don't really allow the frequency to change much without expensive mechanical tuning ...

27

The fundamental laws of EM are Maxwell's Equations: $$\nabla \cdot \mathbf{E} = 4\pi\rho$$ $$\nabla \cdot \mathbf{B} = 0$$ $$\nabla \times \mathbf{E} = -\frac{1}{c} \frac{\partial \mathbf{B}} {\partial t}$$ $$\nabla \times \mathbf{B} = \frac{1}{c}\left( 4\pi\mathbf{J} + \frac{\partial \mathbf{E}}{\partial t}\right)$$ They have always been the fundamental ...

27

Because the assumptions required by the lumped element model are violated. The lumped element model is what allows you to analyze devices like resistors connected by nodes, without considering the physical layout of devices and the circuit. The lumped element model assumes: The change of the magnetic flux in time outside a conductor is zero. {\frac {\...

25

There are several reasons. 1) Soldermask is lossy, and different types of mask are differently lossy. So having no soldermask where the RF fields are gives the best transmission, and if your board is made by different fabs, the most repeatable transmission. 2) Line dimensions, which affect characteristic impedance, are critical. It's difficult to optically ...

24

There is lot of complicated (and right) answers here. I will add one simple analogy - think of shooting gun: at 10 cm distance, the time of bullet travel is just distance/velocity and hitpoint is on line identical to axe of the barrel at 10 m distance you see, that the bullet hit the target lower, as gravitation pulled it little down and you have to adjust ...

24

Your tooling seems to be the cause there, not the cable. From https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1428419&nid=-32775.536879654&id=1428419 The 4294A extends its measurement frequency range up to 110 MHz by terminating each measurement terminal with 50 ohm in order to eliminate the resonance of test leads (...

23

Responding to your title: Am I insane to question that only with a closed path can electrons move? Currents usually* travel in loops. However, the loops need not be entirely made of conductors (ie, copper). Current is a flow of charge. Therefore, all the following physical phenomena represent current: Electrons flowing in a copper wire Ions (which are ...

23

The input impedance of certain devices/circuits (transformers) does not neccessarily need to match their output impedance. Consider a 50Ω (or whatever impedance) antenna as transformer that transforms 50Ω (wire side) to 377Ω (space side). The impedance of the antenna is not (only) given by the impedance of free space but (also) by the way it is constructed....

21

I think this blog post answers your question pretty well :) Demystifying RF Circuit Design – The art of Voodoo In short, the 3 main components illustrated are: hair-pin type band-pass filter distributed element low-pass filter (regularly-spaced rectangles 'dumbells') series LC resonator (the radial stubs off one side of the trace) See the referring page ...

21

Length matching is about timing so if you want to know how tightly you have to length match you have to understand the timing budget for your interface. Signals will leave your source, and arrive at your destination with some timing relationship. Your receiver requires a certain timing relationship between clock and data in order to be guaranteed to ...

21

This isn't true. It's perpetuated by a misunderstanding of a real phenomenon called skin effect: Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor. The electric ...

20

Something as simple as a cable does not have discontinuities like that. There may be a clue in the fact the problem occurs at a nice round number, 5MHz. Is this a place where your test set changes ranges? Maybe it changes output amplifier, or filter, and one of them is broken or damaged. The fact that you've quoted measurements at 4.99MHz and 5.01MHz ...

19

In addition to the reasons given by Niel_UK, there is the matter of predictability and modeling. Soldermask is applied as a liquid. As such, its thickness may not be as well controlled and predicable as the thickness of the substrate and conductor layers. In addition, it may have an unpredictable profile - how does it "flow" in between the traces? All of ...

17

All the answers name some valid points, but they fail to really answer the question which I want to repeat for clarity: Why is 50 Ω often chosen as the input impedance of antennas, whereas the free space impedance is 377 Ω? The Short & Simple Answer These two impedances have no relation at all. They describe different physical phenomena: the antenna ...

15

Rule #1. There is no such thing as an open circuit except under DC steady state conditions. Between every wire, every part and even every atom, there is capacitance, resistance and inductance to some other wire, part and atom. Microscopic as it may be, it is there. Even within the wire or part itself. However, if the circuit you are testing is in a steady ...

15

The expression "capacitance changes depending on DC bias" is a bit misleading. It actually comes from the fact it is tested with a DC bias and a tiny AC voltage added to it to measure the capacitance. But in reality, the capacitance of any capacitor always depends on the instantaneous voltage across the capacitor, no matter where this voltage came ...

14

The LTC1799 can be programmed by a resistor and a link to produce a vast array of frequencies. Is there a small (6-pin) DIP I can use to generate multi-MHz squarewave clocks with an external crystal? It's certainly small It's 5 pins not 6 It's not DIP but you want "small" and DIPs are not small in comparison to SM devices. It doesn't use a crystal

13

It's an insulating, flame retardent polyester tape normally used within the layers of transformers to enhance the breakdown voltage capability between primary and secondary. 3M describe it as: - Yellow polyester film tape with an acrylic adhesive. This tape is suited to coil wrapping, wire harnesses, fractional horsepower motors any many more uses. ...

13

Basically you want something close enough to the pin that at the edge rates in play the bounce is not too bad, and then something further away with (possibly) enough ESR to damp everything to keep the far higher ESL of the supply wiring from screwing things up. ESL is the critical thing, not in the first instance capacitance and that is almost wholly driven ...

12

The largest single factor is usually inductor size. If you eg double frequency you can generally halve inductance (as the impedance of a pure inductor is proportional to frequency). In practice a number of factors apply so that it's not a directly linear relationship, but good enough. If you need a peak current of say 1A then the time taken to ramp up from ...

12

This is a crosstalk question as I understand it. JTAG is single-ended typically 3.3V signal swing. This can couple to your differential signals (which are most likely LVDS with much lower voltage swing) and create logic errors. The other way around is also possible (the LVDS signal coupling to the single-ended JTAG signal). As I understand it this is ...

12

Trace length versus frequency - for sending data or carrier waves between one IC and another, the guidelines are fairly tolerant I'd say. The maximum frequency that could be generated in significant amounts (maybe up to several harmonics for a square wave) is the limiting factor and if your trace length is "less-than" one-tenth of the wavelength then you ...

12

I've been curious for awhile now ... and was wondering if there exists components that provide clocks much faster than a typical CPU can, such as up to 10 GHz or higher. Opto-electronic Oscillators (OEOs) are oscillators that take a photonic signal, like a pump laser, modulate it, and convert it to an electrical signal using a photodiode. The signals ...

12

Aside from the lossy nature, solder mask has a high dielectric constant relative to air and poorly controlled thickness, so the characteristic impedance will be harder to control with solder mask applied. Zo decreases by about 1 Ohm / mil of soldermask thickness. LPI solder mask affects Zo by about 2 ohms and dry film by as much as 7 ohms.

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Yes, you can make a Pierce oscillator with one chip and a resistor and the two load capacitors, plus maybe a series resistor if the drive power is too great for your particular crystal. The inverter must be an unbuffered type or it will likely do all kinds of undesirable things such as oscillating at two frequencies at once. Here is TI application note on ...

12

Skin effect is well-documented and that good documentation, I believe, tells you exactly what you need to know; As a conductor's DC resistance increases, then skin effects are less noticeable. Extract from wiki: - In a good conductor, skin depth is proportional to square root of the resistivity. This means that better conductors have a reduced skin ...

12

The domestic microwave oven needs high power to cook the meal and high frequency to excite the water molecules. What is not needed is high stability because the water energy absorption spectrum is broad. (1, 2) The magnetron does this cheaply. The low price and low duty cycle of the domestic microwave means that they should last for many years despite ...

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