# A general detectable frequency, everywhere? **URL:** \ **Category:** Factual Questions\ **Created:** [April 6, 2018, 4:05pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929 "2018-04-06T16:05:32Z")\ **Posts on this page:** 15\ **Page:** 2
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [April 6, 2018, 9:03pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/21 "2018-04-06T21:03:49Z")
> [@cmyk](#): > > Would something like the [WWVB signal](https://en.wikipedia.org/wiki/WWVB) for atomic clocks work? I don’t think you will receive it “everywhere on the surface of the Earth”. And will resolution be better than DGPS? I kind of lost track of what the OP was building. ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [April 6, 2018, 9:05pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/22 "2018-04-06T21:05:16Z")
Yeh, I realize, but other than the DGPS, I don’t think there’s much of an option. As **scr4** noted, most natural options are very weak or directional, or both. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 6, 2018, 9:11pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/23 "2018-04-06T21:11:55Z")
> [@DPRK](#): > > I kind of lost track of what the OP was building. I’m [thinking a device to prove that time doesn’t exist](https://boards.straightdope.com/sdmb/showthread.php?t=740660). ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [April 6, 2018, 9:15pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/24 "2018-04-06T21:15:37Z")
> [@Darren\_Garrison](#): > > And as I linked to in the other thread, there is a class of sensor that uses tiny heaters and thermometers–some sealed-in air is heated and any movement causes the air to move, allowing the thermometers to detect the temperature change and thus the acceleration. There are literally no moving parts in the sensor other than air. And they cost a dollar or two in bulk. (Probably can be bought for a few dollars individually from resellers.) If that isn’t good enough for the OP’s restrictions, then he really will be waiting until Hell freezes over. That’s interesting. I will take a look at those. Our equipment may be used in +/- 40 C conditions. But the external temperature changes are slow, so the short periodic sample time would not be troubled too much by that. If the devices can maintain proper function at those extremes. If they use self contained differential it should be okay. The movements are low frequency. Geophones are often 8 Hz resonant. The sample period is less than a minute. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 6, 2018, 9:24pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/25 "2018-04-06T21:24:56Z")
[Here](http://www.memsic.com/userfiles/files/Datasheets/Accelerometer-Datasheets/DTOS_MXC6255XC_Rev_E.pdf) is the data sheet for the 90 cent model–temp range of -20C to 70C. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [April 6, 2018, 9:26pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/26 "2018-04-06T21:26:10Z")
We use all sorts of instruments. We destroy all sorts of instruments. Even the mems ones. The mems sensors themselves are very tough. But the support circuitry fails due to extremes of temperature. Physical abuse. Water infiltration. They are also larger than the analog phones. Much more expensive as well. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [April 6, 2018, 9:31pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/27 "2018-04-06T21:31:00Z")
Thanks Darren. Do you happen to know if there are ones that output the raw analog voltage? Currently all our instruments do 24 bit A/D conversion. So I can put the raw analog out into our convertors. Our max sample rate is only 4 milliseconds. I can search that out, now that you have put me onto the path. But if you happen to know… ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [April 6, 2018, 9:38pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/28 "2018-04-06T21:38:34Z")
Never mind. See them on the manufacturers chart. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 6, 2018, 9:39pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/29 "2018-04-06T21:39:14Z")
> [@Kedikat](#): > > Thanks Darren. > Do you happen to know if there are ones that output the raw analog voltage? I didn’t even know they existed until earlier today when I saw “thermal” listed as a type on the Wikipedia entry for accelerometers. The site’s documentation seems to be very detailed, though. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [April 6, 2018, 9:50pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/30 "2018-04-06T21:50:02Z")
> [@Darren\_Garrison](#): > > I didn’t even know they existed until earlier today when I saw “thermal” listed as a type on the Wikipedia entry for accelerometers. The site’s documentation seems to be very detailed, though. Strange. They do an internal A/D conversion after gain. Then a D/A of that for output. Then we would do another A/D conversion. The distortion and noise are going to really build up. But I will keep looking. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [April 6, 2018, 11:23pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/31 "2018-04-06T23:23:09Z")
Seismologists use GPS averaged over very long periods to detect millimeter-scale movements of the Earth’s crust. There are all kinds of noise sources, from the ionosphere and elsewhere, but they average out over time. This will only work on week+ timescales, though. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [April 6, 2018, 11:56pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/32 "2018-04-06T23:56:51Z")
Why not solve the Environmental issues with sensor encapsulation? That thermal chip above can only detect shake and 0.5G and it sounds like it is the FP4, wiring etc… that is the problem, just appropriate potting inside of an appropriate enclosure should solve that issue. ---
**Author:** ![brujaja](https://avatars.discourse-cdn.com/v4/letter/b/4af34b/32.png) [@brujaja](https://boards.straightdope.com/u/brujaja)\ **Post date:** [April 8, 2018, 10:59pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/33 "2018-04-08T22:59:07Z")
This might be the right place to mention something odd that a radio-literate friend and I noticed. (or not. Dunno.) We were experimenting with some equipment. We set up a radio antennae and attached it to the leads of an oscilloscope. We picked up a signal that was obviously an ordinary local radio signal. However, the signal, which you understand is an audio signal, not meant to be looked at visually, was blipping – jiggling visually on the scope – in what appeared to be Morse code. Not sure how you would do that; but it would be a great way to communicate covertly. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 9, 2018, 12:14pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/34 "2018-04-09T12:14:49Z")
Lightning strikes cause the earth and its ionosphere to “ring” at very low frequencies. See [Schumann resonances:](https://en.wikipedia.org/wiki/Schumann_resonances) the frequency, Kenneth, is right around 8 Hz. This is related to the time-of-flight for the wave to propagate to the far side of the earth and then back again. ---
**Author:** ![EdelweissPirate](https://avatars.discourse-cdn.com/v4/letter/e/8491ac/32.png) [@EdelweissPirate](https://boards.straightdope.com/u/EdelweissPirate)\ **Post date:** [April 9, 2018, 12:19pm UTC](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929/35 "2018-04-09T12:19:14Z")
> [@Machine\_Elf](#): > > […] the frequency, Kenneth, is right around 8 Hz. I suddenly have a hunch about Machine Elf’s real-world identity. Dan Rather? [Is that you](https://www.nytimes.com/1997/01/30/nyregion/belatedly-the-riddle-of-an-attack-on-rather-is-solved.html?pagewanted=all)? [Previous page](https://boards.straightdope.com/t/a-general-detectable-frequency-everywhere/811929.md?page=1)