Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Jeroen Belleman Newsgroups: sci.electronics.design Subject: Re: OT: sound speed depends on frequency on mars Date: Sun, 1 Sep 2024 20:37:29 +0200 Organization: A noiseless patient Spider Lines: 204 Message-ID: References: <2uu3djptvil2j5vberhsj4otm3nbd6l557@4ax.com> <0797djh7b67m0htlvush9uk6e6j33k0cd8@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sun, 01 Sep 2024 20:34:30 +0200 (CEST) Injection-Info: dont-email.me; posting-host="1566ab80bd259a9b5ee3988cbdb647e1"; logging-data="1678248"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19w223CBG/Bqf7s3imzIFgz" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Cancel-Lock: sha1:vj/pn+aXj/uwMi03FoLjFG69QIA= Content-Language: en-US In-Reply-To: <0797djh7b67m0htlvush9uk6e6j33k0cd8@4ax.com> Bytes: 10086 On 9/1/24 01:32, john larkin wrote: > On Sat, 31 Aug 2024 22:52:08 +0200, Jeroen Belleman > wrote: > >> On 8/31/24 21:31, john larkin wrote: >>> On Sun, 1 Sep 2024 02:37:22 +1000, Bill Sloman >>> wrote: >>> >>>> On 1/09/2024 12:18 am, john larkin wrote: >>>>> On Sat, 31 Aug 2024 16:17:39 +1000, Bill Sloman >>>>> wrote: >>>>> >>>>>> On 31/08/2024 3:10 am, john larkin wrote: >>>>>>> On Sat, 31 Aug 2024 01:23:19 +1000, Bill Sloman >>>>>>> wrote: >>>>>>> >>>>>>>> On 31/08/2024 12:34 am, john larkin wrote: >>>>>>>>> On Fri, 30 Aug 2024 11:13:05 GMT, Jan Panteltje >>>>>>>>> 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? >>>>> >>>>> Because dielectrics are imperfect, especially FR4, and because there >>>>> are lots of papers online that analyze dispersion in stripline. >>>> >>>> But you can't cite any of them. >>> >>> Can't you google? >>> >>> >>> You wouldn't use FR4 around a stripline >>>> if you wanted a low-dispersion transmission line. There are better >>>> substrates his frequency work. >>>> >>>>>>> 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. >>>>> >>>>> And eventually the trace has to be skinnier than PCB houses are >>>>> willing to etch. >>>> >>>> Why? >>> >>> Run the Saturn program. More layers make the dielectrics thinner, so >>> to maintain a useful impedance the traces have to get narrower. >>> >>> 10 layers gets nasty. >>> >>> >>> >>>> >>>>> Standard pricing seems to be around 5 or maybe 4 mils >>>>> width these days. We do a lot of 5, to sneak between BGA balls, but >>>>> sometimes even 5 is too big. >>>>> >>>>> Thin dielectrics have tolerance issues too. I'm talking about real >>>>> PCBs here, not ideal theoretical stuff. >>>> >>>> Printed circuit board are always real. >>> >>> Exactly. >>> >>>> >>>>>> Pay enough for close-tolerance substrates in the two relevant layers and >>>>>> you should be okay. >>>>> >>>>> "Pay enough" can get crazy fast. I don't want to pay hundreds of >>>>> dollars for a smallish PCB. >>>> >>>> An eight or ten layer PCB isn't going to be small. You only need lots of >>>> layers when you have to connect lots of stuff. >>>>>>>> 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. >>>> >>>> John snipped the rest of that senstence, without marking the snip. >>>> >>>>>>>> You can make lumped constant transmission lines by linking a >>>> series >>>> of capacitors with discrete inductors, if you want a high >>>> impedance >>>> transmission line - people sold them as thick film hybrid >>>>>>>> assemblies, and I even used a few, a very long time ago. >>>>>>> >>>>>>> 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. >>>>> >>>>> I certainly had the idea. >>>> >>>> In a remarkably half-baked way. >>> >>> Ideas start out fuzzy, or at least they should. I tell my kids, stay >>> confused for a while. >>> >>>> >>>>> I might Spice a bunch of ltlines with >>>>> inductors between, just for fun. It's unlikely that I'd use such an >>>>> arrangement in real life, but it's just possible, especially if analog >>>>> quality of a fast edge matters, like in a laser modulator maybe. It's >>>>> preferable to just keep all the traces very short, but that's not >>>>> always possible. >>>> >>>> You seem to be intent on re-inventing the lumped constant delay line, >>>> without being aware that they were commercially available some thirty >>>> years ago, back when I used them. They may still be available. >>> >>> The Tek 545 30 MHz scope had a gigantic, lumped, tunable, differential >>> delay line up to the CRT, so you could see the edge that you triggered >>> on. >>> >>> https://w140.com/tekwiki/images/thumb/1/10/Tek_545a_delay_close.jpg/231px-Tek_545a_delay_close.jpg >>> >>> A lossy pcb trace with periodic loading coils is not a lumped-constant >>> tx line. In fact, lumped lines are nasty. The number of sections goes >>> as Td/Tr squared, which can get awkward fast. >>> >>> Meander-line sections connected by loading coils could be interesting. >>> One product that I'm considering now is a programmable delay line, and >>> that idea might help. >>> >>> >>> >> >> In the 1980's we had NIM-format boxes with binary-weighted-length cables >> and cheap slide switches, and CAMAC modules with basically the same >> cables, but with fancy miniature DPDT relays in metal TO-8 style >> packages. Physicists would invariably mess up the relay contacts. >> >> Jeroen Belleman > > I was thinking of using the cute little $1 Fujitsu telecom relays, > which are good up to about 3 GHz. > ========== REMAINDER OF ARTICLE TRUNCATED ==========