Hi

Just a few curiuos questions (never whent into the deep on this subject at school)

I dont have the intention and time to play around with it.

First at what frequency does this effect starting place.

and if you double the frequency does it means that the core of the cable that dosn't transport the electrons get linear bigger.

and what if we use a metal pipe as (cable) is it an idea to cool it with a liquid (oil is a not conducting cooling liquid)

second does it only work with AC or do we also have this effect with a DC voltage with a varying top value

Robert-Jan

 

It always occurs. It's just that the effect at lower frequencies and the specific material does not have a big enough effect for us to take the effort to do something about it.

Probably not a good idea. Materials that make the best conductors usually don't make very good pipes and materials that make the best pipes usually aren't very good conductors. Plus, a pipe carrying something has to be thick enough to be strong which means it has to be thick which robs a lot of surface area. A stranded wire would be more effective.

??? It works at all frequencies. Higher frequency components of the electrical current won't be able to use as much of the conductor's cross section to flow as much as the lower frequency components can. Physics does not care if it is pure DC (0Hz), pure AC (>0Hz), or AC with a DC bias. Each frequency component is treated separately.

What does the bolded section mean? Are you familiar with fourier analysis? Because that question does not make a lot of sense...varying voltage means AC. Do you just mean an AC signal with a DC bias?

 

Copper makes great pipes, is a reasonably good conductor, and there are applications with internally cooled copper coils. Silver and gold also make good pipes, but are a bit expensive. Silver is particularly good for small bore hollow tubing.

John

 

That's Exacly what I mean

The thing is that the proper name or term for this doesn't stick in my head.

Robert-Jan

 

Copper pipes are perfect for high-frequency, high power applications where you need cooling. Even if you don't need cooling they are good. Lots of induction heater coils use them.

 

Is there a simplest type of shape with a large flat surface that would have a unique current density at all points on the large flat surface?

 

Well, sorry to say, it is not a new idea. Ever hear of microwave pluming? Flexible pipes are often used in very frequency and often times the pipes are filled with gas that will not readily condensate with temperature changes. Even moister will cause standing waves in these wave guides used as transmission line.

Yes skin effect is more & more critical as the frequency increases. This is why the PCB layout is also critical. I mean the layout is everything. You can even make filters by doing your layout certain ways. Not just comb filters, but the angles of the trace as well.

 

yes i wired an RIAA preamp following the PCB layout but still ended up with a radio instead of a preamp....

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What do you mean, a "radio"? You mean an oscillator?

 

nope I could actually hear very faintly speech ! don't know what language it was in though

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www.simonsphotography.org.uk/ - My other hobby
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Never buy "Trust" products, all mine broke !!!

 

No kidding? I would like to see your schematic. You are probably picking up local broadcasts. Still, if you thought it was simply a pre-amp, it could be something interesting but it is not uncommon to receive unwanted local broadcast in a normal receiver. What is usually done is to use some form of band stop filter. This may be necessary in your pre-amp. It must be very sensitive. One other question. Do you live near a broadcast station? I live so close to one that I can put my hand on a probe from my freq. counter and read it's frequency.

 

well i was living in italy at the time and to my knowledge there were no local broadcaster minus the probably illegal transmissions from "radio maria" in the church about 4 miles away. I'm pretty sure they were transmitting as when I walked behind the church with my portable radio (in later years I lived closer to it) I could only pick up that station no matter what i tuned to.

However like i said what i got sounded foreign to me (foreign that is to both english and italian) so it was not local. I've lost the schematic of the preamp but it was just a normal RIAA preamp. the instructions were clear that it had to be a PCB, not having access to the equipment I did it on matrix board (not the strip kind) and ran transformer wire in the positions that the PCB layout showed, still i was unable to make it work, I just got this weird radio tansmission. it was also coupled to a small power amp with perhaps more cable than recomended so its no wonder starnge things took place.

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

www.simonsphotography.org.uk/ - My other hobby
www.rushdenrotaract.org.uk/ - make a difference and have fun !


Never buy "Trust" products, all mine broke !!!

 

Hi,


Skin effect is an effect that tends to increase the AC resistance of a conductor
and the effect increases with increasing frequency.
The magnetic effects push charges closer to the surface so that the conductors
current density near the surface is greater than the density near the axial center.
Since most conductors have a round cross section, this means most of the
conduction happens near the surface and much less near the center so even
though the conductor is solid it starts to act as a conducting tube instead.
The thickness of this tube is said to be the "skin depth".
Because of this action we loose some of the cross section of the wire, and
the cross section determines the resistance of the wire in that if we halve
the cross section we double the resistance. This can be a problem, and
the skin effect means that our wire is not as effective for AC current as it is
for DC current where no effect takes place.

The change in current density means the AC resistance goes up, and that
can be a problem when we need the full bulk of the wire conducting in order to
meet other circuit requirements.
To get around this sometimes more than one wire is used in parallel, and because
more than one wire is used the diameter can be reduced, meaning several wires
can fit in the same space that the original heavy wire first took up. The advantage
here is that now the skin depth will be equal to the radius of the wire, and so
the entire (smaller) wire cross section will be utilized in current conduction and
so the AC resistance is reduced.

One of the ways to deal with this is to do a few calculations at the frequency of
operation and compare the AC resistance to the DC resistance (where no skin
effect takes place) and decide if the application is still acceptable or not.
Im sure there are formulas on the web that can be used to do these calculations.
If there looks like there will be a problem, steps can be taken to improve the design
such as using multiple strand wire or sometimes simply going bifilar. An acceptable
design is usually reached when each wire radius matches the skin depth.

When you have a DC current alone there is no skin effect, but when you have some
AC present also then there is some skin effect. Since pulses are composed of
various components of AC signals of various frequencies, the effect on each
of these frequencies will be different. The conductor will act as a sort of
low pass filter, in that higher frequencies will be attenuated more than lower ones.
The total extent of this filtering action would have to be calculated to better
understand what would happen.

 

It's down to either poor design or poor construction, and certainly isn't unknown - correct design includes components to avoid such propblems (some were called grid-stoppers back in the distant past), plus careful construction - a shielded box is a good start.

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well it was a design from a not very good magazine that was always making mistakes, I hated their very long winded and so called explanatory theoretical articles that ran round and round and said nothing in the end.

the construction was certainly poor as well as I was not at all equiped

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

www.simonsphotography.org.uk/ - My other hobby
www.rushdenrotaract.org.uk/ - make a difference and have fun !


Never buy "Trust" products, all mine broke !!!