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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: OT: sound speed depends on frequency on mars
Date: Sat, 31 Aug 2024 16:17:39 +1000
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On 31/08/2024 3:10 am, john larkin wrote:
> On Sat, 31 Aug 2024 01:23:19 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
> 
>> On 31/08/2024 12:34 am, john larkin wrote:
>>> On Fri, 30 Aug 2024 11:13:05 GMT, Jan Panteltje <alien@comet.invalid>
>>> wrote:
>>>
>>>> NASA's Mars rover Perseverance has found that sound travels much more slowly on the Red Planet than it does on Earth
>>>> and behaves in some unexpected ways that could have strange consequences for communication on the planet.
>>>> https://www.space.com/nasa-mars-rover-perseverance-speed-of-sound#main
>>>>    At frequencies above 240 Hertz, "the collision-activated vibrational modes of carbon dioxide molecules do not have enough time to relax, or return to their original state,"
>>>>    the researchers said, which results in sound waves at higher frequencies traveling more than 32 feet per second (10 m/s) faster than the low-frequency ones.
>>>>    That means that if you were standing on Mars, listening to distant music, you would hear higher-pitched sounds before you would hear the lower-pitched ones.
>>>>
>>>> paper:
>>>> https://www.hou.usra.edu/meetings/lpsc2022/pdf/1357.pdf
>>>>
>>>> So...
>>>> Music from far away may sound funny?
>>>>
>>>> For Mars we will need compensation headphones with distance measurement and variable delays....
>>>> ;-)
>>>>
>>>> Better use radio.. and earplugs/ headphones...
>>>
>>> Funny, I just delivered a lecture on transmission lines and noted that
>>> microstrips have dispersion from  the unbalanced dielectric constants
>>> and skin effect. Rising edges get sloppy at the and of a long trace.
>>
>> I hope you pointed out that buried strip-line isn't dispersive. I have
>> pointed this out here from time to time.
> 
> Of course it's dispersive, maybe a bit less than microstrip.

Why do you think that?

> It's hard to keep up decent impedances on stripline in a multilayer
> board, especially 8 or 10 layers.

Stripline is buried between two ground planes. The only tricky part of 
impedance control is the thickness of the dielectric in the two layers 
above and below the strip-line. In a ten layer board this is thinner 
than it would be in a board with fewer layers.

Pay enough for close-tolerance substrates in the two relevant layers and 
you should be okay.

>> https://www.wevolver.com/article/stripline-vs-microstrip
 >>
>>> I wonder if anyone has added surface-mount Heaviside loading coils to
>>> a PCB trace.
>>>
>>> https://en.wikipedia.org/wiki/Loading_coil
>>
>> It would be a bit silly.
> 
> Most ideas seem silly to people who are by nature hostile to ideas.

Not a problem I've got.

> Dismissing is easier than thinking.

Thinking about what a loading coil might be doing to the impedance of a 
PCB trace isn't something that you seem to have managed to do.

-- 
Bill Sloman, Sydney