On 10/15/2018 07:20 AM, Karl wrote:
On 10/14/18, Mirimir <mirimir@riseup.net> wrote:
I worked on this for a while. I was thinking about compartmentalizing services in multiple Raspberry Pi, connected via opto-isolators. Like Markus Ottela's Tinfoil Chat,[0] but expanded to work more like Qubes. And indeed, the Qubes team have announced work on Qubes Air:[1]
| This approach even allows us to host each qube (or groups of them) | on a physically distinct computer, such as a Raspberry PI or USB | Armory. Despite the fact that these are physically separate devices, | the Admin API calls, qrexec services, and even GUI virtualization | should all work seamlessly across these qubes!
But, you know, I wondered about EMF cross-talk between qubes. So I decided to learn how to measure that :)
How far did you end up getting on this?
I gave up :( Basically because professional signal/spectrum analyzers cost so much. For example, used Tektronix RSA306 (9kHz to 6.2GHz) go for ~$3000. And you really want something that detects higher frequencies, such as an Anritsu MS2850A (9 kHz to 44.5 GHz). I can't even find used ones, but I'm guessing several $1000. Maybe less-expensive alternatives that are good enough. I find a lot on <https://www.ebay.com/bhp/rf-spectrum-analyzer> and <https://www.used-line.com/list-signal-analyzer>. For example, Anritsu models: <https://www.used-line.com/list-signal-analyzer/communication?ManufacturerIDs=12>. But ignoring stuff over ~6GHz might be problematic.
I don't have any formal training and have developed some cognitive issues, resulting in slow progress, but this is all I am spending my free time on. I do not work a job, being supported for now by a trust.
Yeah, me neither. But no trust :(
Maybe we can help each other. Do you have any experience with funding platforms like opencollective.com or something?
No.
My trust is small. I'm happy to share as much as it will allow me to, but maybe if we could use something general, donations would eventually come in.
Thanks :) But I'm not qualified, so hey.
I'm currently residing in Green Bank, WV, where emissions are regulated for a radio observatory. I am trying to develop some relatively simple software using the rtl-sdr to measure the power of a noise source independent of background traffic, so as to quickly and repeatedly measure shielding effectiveness.
I tried that approach. And it was a nightmare. The setup -- SDR stick, upconverter and laptop -- generated far too much EMF noise. I played with testing stuff in a Faraday cage. But I didn't manage a signal feed to the SDR etc that didn't introduce unacceptable noise.
My current setup is an oscillating noise source powered by a single-board computer that toggles a relay, turning it on and off at a consistent rate.
By averaging the noise level when the source is powered, and averaging the noise level when the source is unpowered, over many thousands of samples, I believe I can determine the power of the emitter without regard to background noise by comparing the statistical distributions of the two sets of samples.
I make the assumption that the foreground signal is the arithmetic sum of the generated noise and the background noise.
Any thoughts?
That sounds reasonable. But again, I did some RF stuff in physics lab, and that was a _long_ time ago ;)
I believe that you'd need professional equipment, which is properly shielded, and doesn't bleed noise into the testing environment.
Have you tried or researched any professional equipment to report back? I haven't, at this time.
As noted above, it seems that https://www.used-line.com is a good source. And eBay, of course ;)
I then plan to try to measure a variety of setups ranging from homemade aluminum foil & iron paint to soldered copper and welded or bolted stainless steel, to identify ways for everyday people to cheaply create shielded environments that are actually effective. I would like to find a way people can use off-the-shelf supplies to make environments that are isolated from DC to light, if desired.
That is also harder that it might seem. For high frequencies, with very small wavelengths, even tiny cracks are enough to leak horribly. You need joints with elastic seals, to mitigate against misalignment and wear. Such as beryllium copper finger strips, elastic beryllium copper tubular braid, etc.
I've looked into that a little. After skimming through some shielding books, I've got the following thoughts:
Permanent Seams: - Alu foil can be stapled or tightly taped (see David Weston's paper on aluminum foil rooms) to increase its frequency range. I expect using a wire brush to remove oxidation, and tightly flattening it, would help too. Testing is needed to see if this is worth the effort. - Metal filings can be mixed with paint. This allows for tight sealing, but the conductivity is likely poor. Advantage is that sweepings are available for free. Testing needed. - Metal can be tightly bolted, as is done for modular rooms. The bolts must be frequent and close, to pull microvariations of the metal into each other. - Steel can be welded. This is the gold standard. Welding is not that hard. - Copper can be soldered. This is easier than welding !
Temporary Seams: - Fingerstock is purchasable and not that expensive, but complicated and needs cleaning. - Bolts can be temporary, to bolt a door on as modular walls are bolted together. It's laborious, but it's workable and cheap and doesn't require mail-order. A robot could tighten and loosen them. Testing needed. - A door could perhaps be given pressure that does not penetrate it, to keep a tight seal, perhaps via an automatic mechanism. Cleaning will be needed. Testing too. - A copper door could be actually soldered closed, and then desoldered to open it. A robotic door could automatically do this. Very tight. Research needed.
My understanding is that high frequencies are attenuated mostly by reflection. Hence I'd expect these tight seals to be needed mostly for very thin, highly conductive material, which could keep costs down if true.
That's consistent with what I've read.
Karl