Well crap that didnt work
I blame Google
So these images show a trace above a ground plane and the field around it.
Got it, thanks
strawberry fields forever?
So when we DONT match the impedance a reflection occurs. Truth be told we live with tehse reflections all over the place but...
Enter the series resistor, I used to put 22 Ohm resistors in series to absorb the signal that got away from me and is bouncing up and down the trace
are termination resistors fitting into this picture too or no?
A reflection occurs when the receiver doesn't absorb 100% of the signal
if the transmitter is 50Ohms and the receiver is 55 ohms than a percentage will be reflected.
If the transmitter doesn't absorb it it will be reflected again
Is that kinda clear or should I talk more about absobing the reflection when they ARENT matched?
By the way, my CAD package calculates the trace width for me
Eagle might, Ted you still there?
Labcenter makes Proteus. Kicad also will with the right addon
So from my understanding by adding a serial R on the tx side we allow the signal to reflect from unmatched receiver and to be absorbed at the receiver side. And that does not influence the reception quality because the receiver does not "see" the reflection caused by itself?
Yes. AND its not radiated as much and it doesn't keep bouncing around creating noise, including FCC emmision noise
I think using firehose to fill a small cup vs. using garden hose vs. using garden hose with restrictor attachment
is that right direction? "spilled water" in my analogy would be reflected signal
I am trying to get images off my CAD station but the image upload problem is making it tough
Think of a trough of water.
But the restrictor is on the tap and the cup is a closed system
and a wave
Cheap PCB material has a more variable Dielectric constant and more absorption in general usually. Oshpark has a good hi freq material (FR408) for their 4 layer boards and JLBPCB has some Rogers materials available (I use 2313)
Flex pcb material polyamide also has good hifreq properties.
Also before I forget there are great calculators for some of this online. So if I move into wave length these here may help: https://www.microwaves101.com
As frequencies go up, the distance represented by a wavelength goes down.
Everyone understand what I mean by wavelenth? Basically Planks constant and why those little holes in yoru microwave oven door let light out but keep microwaves in
250 mhz has a wavelength of 47”, 500 mhz has a wavelength of 23”
Sounds huge right!
When a trace gets to be 1/4th of a wavelength we really DO need to start using atransmission line
(transmission line = stripline = trave over ground plane)
So if we have 500mhz component, anything near 6”/150mm or greater needs to be done as transmission line known as a microstrip and others like stripline, waveguide, etc
so think 500Mhz and 6" , at 500 mhz RADIAN Freq or rise time
the trace officially...
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