104 votes
Accepted

Why do fundamental circuit laws break down at high frequency AC?

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 ...
JRE's user avatar
  • 71.4k
55 votes
Accepted

Am I insane to question that only with a closed path can electrons move?

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 ...
Dave Tweed's user avatar
  • 173k
36 votes
Accepted

Why do microwave ovens use magnetrons?

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 ...
Spehro Pefhany's user avatar
29 votes

Why do fundamental circuit laws break down at high frequency AC?

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 ...
τεκ's user avatar
  • 4,249
28 votes
Accepted

Why solder mask are not applied to RF PCBs

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 ...
Neil_UK's user avatar
  • 166k
27 votes

Why do fundamental circuit laws break down at high frequency AC?

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}} {\...
Cort Ammon's user avatar
  • 2,916
26 votes
Accepted

Why is 50 Ω often chosen as the input impedance of antennas, whereas the free space impedance is 377 Ω?

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 ...
Curd's user avatar
  • 16.3k
25 votes

Why do fundamental circuit laws break down at high frequency AC?

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 ...
gilhad's user avatar
  • 667
24 votes
Accepted

Why does the cable resistance jump from a low value to high value at a particular frequency?

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 ...
William Lieurance's user avatar
23 votes

Am I insane to question that only with a closed path can electrons move?

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,...
bobflux's user avatar
  • 77.5k
22 votes

Why is 50 Ω often chosen as the input impedance of antennas, whereas the free space impedance is 377 Ω?

All the answers name some valid points, but they fail to really answer the question which I want to repeat for clarity: ...
crateane's user avatar
  • 333
20 votes

Why solder mask are not applied to RF PCBs

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 ...
Joren Vaes's user avatar
  • 12.5k
20 votes

Why does the cable resistance jump from a low value to high value at a particular frequency?

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 ...
Neil_UK's user avatar
  • 166k
17 votes

Am I insane to question that only with a closed path can electrons move?

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 ...
Trevor_G's user avatar
  • 46.7k
16 votes

Placing of capacitor close to IC power pin - logic

The black art of decoupling. The reason you put decoupling capacitors close to the required IC is to supply current for the high frequency signals. This means you want to reduce the inductive loop ...
Puffafish's user avatar
  • 4,136
15 votes
Accepted

If a high frequency signal is passing through a capacitor, does it matter if the capacitor is charged?

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 ...
bobflux's user avatar
  • 77.5k
14 votes
Accepted

Is there a small (6-pin) DIP I can use to generate multi-MHz squarewave clocks with an external crystal?

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 ...
Andy aka's user avatar
  • 457k
14 votes
Accepted

How are RF filters constructed?

As you've discovered, once you are up in the 100MHz+ range, little is "simple". When using discrete capacitors and inductors, you have to consider their parasitic complements. Even basic ...
colintd's user avatar
  • 7,843
13 votes
Accepted

what is the name of this yellow tape around high frequency transformer?

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: - ...
Andy aka's user avatar
  • 457k
12 votes

Why solder mask are not applied to RF PCBs

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 ...
Spehro Pefhany's user avatar
12 votes

Is there a small (6-pin) DIP I can use to generate multi-MHz squarewave clocks with an external crystal?

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 ...
Spehro Pefhany's user avatar
12 votes

Why isn't there a non-conducting core wire for high-frequency coil applications

No, you are correct in the theory, but your approach leads to an unnecessary increase in volume when compared to using flat wire, which is both easier to manufacture and provides a similar advantage ...
John Birckhead's user avatar
12 votes

Skin Effect of resistors

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 ...
Andy aka's user avatar
  • 457k
12 votes

Why do microwave ovens use magnetrons?

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 ...
Autistic's user avatar
  • 14.7k
12 votes

How to calculate values for decoupling capacitors

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 ...
Dan Mills's user avatar
  • 17.5k
12 votes
Accepted

Does the 1x oscilloscope probe setting slow down MHz digital signals?

Not only does the probe have lower bandwidth when in 1:1 mode but there is much greater capacitance load on the source when in 1:1 mode. That extra capacitance will significantly lengthen the rise and ...
Kevin White's user avatar
  • 33.2k
12 votes

Find out value of pF capacitors

We regularly measure C(V) curves of some components such as transistors for validation purposes, where the target resolution is 0.1 pF or better. simulate this circuit – Schematic created using ...
tobalt's user avatar
  • 22k
11 votes

What's difference among impedance analyzer, spectrum analyzer and vector network analyzer?

An impedance analyzer is for measuring impedances, which you could call AC resistance as inductors and capacitors act like resistors with phase shifts at AC. They can be handy for testing filters and ...
Sam's user avatar
  • 3,709
11 votes

How to design a cheap sine-wave generator up to 200 MHz?

Your second idea of using switched low pass filters to pass the fundamental of a square wave is the way it is done in many commercial RF signal generators. It does depend how clean you want your ...
Neil_UK's user avatar
  • 166k
11 votes
Accepted

How is the esp8266 is able to generate 2.4 GHz wifi signals?

The radio contains a voltage controlled oscillator that is locked to an external reference oscillator using a phase locked loop (PLL). This results in a very precise high frequency signal for the ...
alex.forencich's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible