Building Coaxial transmission line on PCB?

PCB

anyway?

Had trouble with crosstalk on a mass of video signals. Cured with a multilayer board where each signal was 'boxed in' by ground plane to the sides, above and below. Sort of square coax.

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Boxed ! the wavelength is far greater than your dimensions , thus higher modes can not exist , thus you do NOT need sides . When you reach 10 Ghz , then maybe you need sides in ur boxed "coax" .

But the big joke , is in the real world , they use cheap PCB to xmit 2.5 Ghz . No strip line , no microstrip , nada .. It works well , so quit arguing reality .

BTW , i saw some novice , trying to use juice cans to launch WiFi . He figured the more cans , the more gain . He had 3 cans , T'd . to divide the power . Gain is not in cans , its in size of the dish .

Another book worm said all i needed was $26 for 100 meters of blah blah coax at 2.5 Ghz ..

At these wavelengths , its lower loss to send it TEM and thru the air , not thru a coax .

This is goin to FPGA ? Do those relics still exist ?! Oh well , i supose ya gotta try to "protect" your firmware by reinventing the CPU !

Seems video distribution is not one of your areas of expertise ?

Note that John was talking about crosstalk, in the analog domain, and yes, what he did certainly will have a measurable improvement, and is somewhat 'industry practise' when minimising crosstalk. Note he says 'cured', that means he is on both sides of the problem, and it is a brave (or something else?) person that counters such direct experience

I imagine in extreme digital cases, such as where you are worried not only about sending the clock, but also about the ps/fs of jitter, then this design approach would also help : it's not hard to do.

-jg

When you need, say, 40x the crunch power of a decent DSP processor, those relics come in handy.

John

I do stuff down to a few ps RMS jitter on a regular 6 or 8-layer board, microstrip traces, with switching supplies and uPs and display drivers on the same board. Picoseconds aren't tough these days.

John

Que?. Don't listen to the worms. Video comes in forms other than digital.

transmitting high-speed signals is very easy when you have a

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You are hoping that we believe switchers cause lots of noise ....

Zero ripple is what switchers do ! The sudden pulse of current is only around a very short loop , it does not cause noise . They dont even have "ground loops"

transmitting high-speed signals is very easy when you have a

Please post the schematic of a zero-ripple switcher.

John

Sorry, but that feature is only available on the 0 volt model.

Indeed there are the topologies of the switchers with exactly zero or almost zero ripple, assuming the ideal symmetry of everything.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

... snip ...

All it takes is an infinite capacity capacitor. The turn-on time and inrush current may be high. However it avoids the need for a UPS. Once they get the breakdown voltage up and get them into production we can have all the electric cars we want, and dispense with all batteries.

Like a polyphase switcher with *big* inductors?

But I don't want "almost zero ripple", I want the real thing.

John

Zero ripple is a real thing. Imagine the two identical bucks operating 50/50 duty with 180 degree phase shift on the common load. Ideally, there will be no ripple at the load at all. There are numerous patents on the variations of this idea, allowing to adjust the duty, different topologies and such.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

Read up on the Cuk converter. Slobodan Cuk's topology.

Without the proper balance, you may get ripple. I've also seen one opinion that the Cuk topology *can't* regulate with a stable feedback but I haven't seen reason for this myself. Simulations with "ideal transformers" back in '89 had input and output currents both going dead-flat solid after the startup.

(posting to the newsgroup I know John Larkin visits, cross-posts removed to the newsgroup I visit)

Right. You'd buy them charged, guaranted to run for 200K miles.

John

This is interesting:

Regards,

Michael

As regulated as a dead short can be. ;-)

This sort of foolish language will sooner or later get you PLONKed

-- "A man who is right every time is not likely to do very much." -- Francis Crick, co-discover of DNA "There is nothing more amazing than stupidity in action." -- Thomas Matthews

Still got that anal/fecal thing going, I see. I'm sure glad I wasn't born with a fetish like that.

John