Large scale RF shielding

Don WHY? wrote: =============

** Like all of your trolls, the crucial facts are missing. If the path to the transmitters is really " unobstructed " and short range, your story is 100% non credible. What is the REAL story ?

BTW: Do you wear a tin hat ?

...... Phil

Must the the foil. What's strange is that it's really hard to build a good EMI screen room.

One trick is to run a wire from outside (as a receive antenna) to inside (as a radiator). I've seen that done in tunnels.

John Larkin <jlarkin@highland_atwork_technology.com> wrote in news: snipped-for-privacy@4ax.com:

Yes. Try to build one and it leaks so bad you can "hear" a pin drop onto a magnet halfway around the world.

This sounds more like cell towers that are turned way down on power due to low utilization of that node.

I remember placing a lot of copper tape to make our quiet cage 'clean'. Have to have a pretty heavy tip on that solder iron too.

It's the wallpaper effect--it won't stick when you're putting it up, and won't come off when you're taking it down. ;)

40 dB loss is a pretty crappy screen room, but will reliably make a mess of cell phone communications.

(We built a test jig out of a big beefy 5x9-inch aluminum die cast box whose lid attaches with a screw in each corner. Turns out that the RasPi inside communicates via wifi quite nicely. ;)

Yup. People have made passive VHF repeaters for amateur radio by putting antennas on each side of a mountain and just wiring them together with coax.

Cheers

Phil Hobbs

NASA uses a passive repeater like that for the moon landings, to get signals from Honeysuckle Creek tracking station to the Deep Space Network site at Tidbinbilla. They had a wired connection as well (just a single telecoms cable pair), following the requirement for everything to be double-redundant. There was a microwave link to Parkes somewhere too.

The repeater tower is probably still there:

There was also a collimating target for aligning the antenna down to the south-west. It's all pretty deep in the mountains, for radio quietness. The Orroral Valley orbital tracking site is south of Honeysuckle too. All the structures down to ground level have been removed now, except at Tidbinbilla.

Clifford Heath.

On a sunny day (Thu, 5 May 2022 11:46:13 -0700) it happened Don Y snipped-for-privacy@foo.invalid wrote in <t5162c$s9f$ snipped-for-privacy@dont-email.me:

Some double glazing also stops RF, I tried my satellite dish inside behind such a window, almost no signal...

Solution, as the dedicated greens will know, is to live in a tent or what's it called 'wigwam'?

Be glad all that RF is attenuated indoors, it interferes with the brain. Some people get sick from it. That said LOL I have been exposed ... a lot, So you see the bad effects it can have.

My 4G internet just uses an USB stick in the window, inserted in an Raspberry Pi programmed as router:

is supposed to be in that vase..

phones works indoors here.. If not I would get a landline... Even DVB-T2 (latest terrestrial TV) works with a simple indoors antenna:

transmitter is miles away.... GPS works, but better upstairs, not always enough sats for positioning downstairs.

Maybe you could get a simple signal strength meter and walk around the house to see where and what attenuates things? Radio with signal strength indicator, I think even one of my phones has a signal strength bar?

Depends on the frequency you want to check.. Spectrum analyzer, using a RTL-SDR stick will show a lot from about 20 MHz up to 1.4 GHz..

of open source software for it, get a 1 ppm one from ebay for about 30 USD. plug into you laptop with a 15 cm piece of wire as antenna, works perfectly.

As others have suggested, I'd also go with the metal foil as the problem, especially as it seems to cover the whole spectrum from a few

10s of kHz (radio clocks) to the GHz range of cellphones. Do you have any wooden doors on the cellphone tower side of the house? Is the cellphone signal level any better "through" those doors than through the house walls? All bets are off if you have metal flyscreens over the doors!

You can get cellphone boosters which have an external antenna and carry the signal indoors, but they would only help with cellphone frequencies. Would an external long-wire antenna with a loop wrapped round your radio clock help with that signal?

That's a bit surprising.

My house is solid wall three bricks thick and I still get enough RF in through the windows for it not to be a problem. They are low emissivity windows too now so I did wonder about it when they were replaced.

The only exception is DAB radio (crock of sh*t) and 2FA texts which sometimes take forever to arrive (so that the website times out before it arrives). Voice mobile calls are usually OK indoors.

Trying to get a 2FA code I sometime end up walking around the highest part of the garden waving my phone high in the air to get signal.

Is there no equivalent of this site in the USA?

Quick overview of what is available and it has links to individual mobile networks claims as to coverage at your location.

To give is a whirl put in a random postcode like TS1 1AA. (that's a fairly non-descript northern city Middlesbrough)

M2 2AA is in Manchester with much better 5G coverage

SW1A 1AA is in London, PM's residence and is as good as it gets.

Or put your phone into engineering diagnostic mode (at your own risk) and you can see carrier details and signal levels in real time then walk round to local masts to see which is which. You might need to do it with a few phones on different networks to get a full picture if they share.

Glass windows usually do that for you.

I'd have thought that a thin layer of aluminium foil or conductive paint would go a long way to providing a decent level of RF attenuation.

ISTR if you are serious about it then you pretty much have to have welded sheet metal construction and beryllium spring copper contacts on all the doors (usually only one double width door on a Faraday cage room) and fancy suppressors on any cables in or out.

Might be easier to start out with a Ford transit van than a house.

High end car theft gangs in Belgium did a pretty good job with lining a largish HVG with supermarket grade aluminium foil and if memory serves lead flashing seals on the opening joints. Good enough Faraday cage to steal high end cars with notional satellite tracking on them anyway.

RF is hard to believe. My key fob will unlock my car from half a block away. We get pictures back from Jupiter. Seems improbable.

It screams very loudly in a medium we cannot perceive. Imagine what it would be like if we could hear RF.

Jeroen Belleman

From the roof of Highland World Headquarters I count about 40 dishes visible with my terrible eyesight. Wouldn't it be cool if the beams glowed at night.

Our internet service is a small dish. We paid for 50+50 Mbps and get

500+500.

There are a number of them, but I don't know which ones are most reliable.

I had not heard of this "engineering diagnostic mode". Turns out that my iPhone 8 supports it. I didn't see anything dangerous, although I didn't look all that hard.

Yes, unless they have some kind of conductive film. Some do.

That kind of construction is not common in the US.

But my house is stucco over expanded metal lath, so it does a pretty good job of blocking cellphone signals.

Yes, this is one way many big shielded rooms are done. The foil is quite thick, and there are multiple overlapping sheets, so the building can expand and contract with seasons without breaking the shielding.

All wall penetrations are filtered and the filter bonded to the shield wall.

The floor is more commonly overlapping sheets of thin galvanized steel.

Yes.

Cute. I assume that HVG is some kind of lorry.

Where do they take the cars to? The tracking will start working once delivered and out in the open, unless they are able to disable all possibilities. So I'm assuming that it is some place without extradition.

Joe Gwinn

We only have views of the horizon through our windows. Most tend to have very

*deep* "coverings" (like porches) to block the sunlight from entering the house when overhead. E.g., I can't see "overhead sky" while indoors. Instead, we see other neighbors' homes.

To get a GPS fix, I have to be outside. Likewise, while garaged, the car doesn't know where it is -- beyond remembering its last position. I've tried this with two (similar) handhelds -- an eTrex Vista and an eTrex Magellan (hacked to power from an external DC source) -- which I imagine are very similar in design (?). Likewise, a pair of "dash mount" Garmins -- a Nuvi 260W and a Nuvi 750 that also suggest some similarities between themselves.

In each case, I set the UUT (only one at a time!) in the center of the living room floor (the room with the least bit of RFI and nothing on the roof, above). I waited 30 minutes for a fix. Then, moved on to the next unit. Nada. Yet all will quickly acquire satellites and yield a fix within a minute or two of being clear of the building. (84 seconds for the Vista, just now, from being powered on from a state where "no batteries installed")

I suspect there's a buttload of RFI in most modern homes -- computers, CFL/LED lights, dimmers, electronic appliances, etc. -- that contributes to poorer reception.

Dunno. I don't use a cell phone for communications; I use them as clocks, PMPs, cameras, TELNET/HTTP terminals... anything BUT a phone! The idea of people being able to pester me at THEIR convenience, regardless of where I am or what I am doing is anathema to me! "Send me an email, I'll get back to you at MY convenience!" (and, of course, THEY can reply to that at THEIR convenience)

My cell phone observations come from noticing the behaviors of my neighbors -- who all step outside to take calls. If they were all having clandestine "affairs" and didn't want their spouses to know, I could understand bearing the "cost" of doing that. In the winter, this is possibly understandable (nice weather) but silly from ~May thru ~Sept (our first 100F day was a week or so ago).

I've no idea as to which carriers they use -- nor the operators of the nearest cell towers (I can see at least three of them within ~0.75 mi of my home... not counting others that may be less noticeable -- or, located away from the roads I typically travel). But, the topography, locally, is pretty irregular; some of the antennae are actually *below* me in elevation (so, I see their signal *through* scores of homes) others above.

There's a site that lists antennae/towers in the area -- it claims 33 towers and 200+ antennae within 3 miles of my location (no idea why it settled on that 3 mi figure). But, I notice that it has no record of the three towers that I know for a fact to be present! <shrug>

I'm not that interested :> My interest lies in sorting out what construction characteristics have had the side-effect of *hindering* reception -- with an eye towards using those (presumably inexpensive, run-of-the-mill) approaches to attenuate interference between adjacent "RF domains" (think apartment house, hotel, resort, office building, etc. where you can expect folks to be operating their own kit "very close" to "your NONEXCLUSIVE RF-space")

One side of the house is essentially "all/mostly glass" (floor to ceiling). Another side has a single small window. The third has just two windows while the last has *none*.

And, windows only look *out*, not up.

I suspect WWV (our time reference) is problematic due to our location in the "RF shadow" of the nearby mountain range (it's a 6000 ft change in elevation beginning just north of our location; i.e., we are in the low spot of the valley).

OTOH, I don't understand why OTA broadcasts (TV/radio) are so problematic. If I had a powerful enough laser, I could illuminate the 5 towers atop that mountain without the beam touching anything along the way ("unobstructed").

If I drop the antennae (from the roof) into the house at the same points (i.e., so the azimuth to the towers is unchanged and the elevation only slightly so), I'll lose most of the signal. I.e., the pathlength has only increased by a few *feet*, no obstructions have been introduced -- just the structure of the house.

That seems to explain many of the "problems", here. Had the masonry walls been the issue, then that would be more challenging to reproduce, elsewhere.

E.g., if a builder can substitute foil-clad drywall for regular drywall and pick up that level of attenuation, it suggests a minor/inexpensive change in construction can help tamp down RF sources from neighboring offices, apartments, suites, businesses, etc. And, something functionally similar to buffer signals coming through floors/ceilings (think 3D).

Not interested in building a Faraday cage. Rather, would like to be able to reduce the "interference" caused by nearby users who happen to be using the same sort of kit. Without having to force them (FCC) to take extraordinary measures to tamp down their emissions.

One would think they would sort out where the antennae are located in each model and simply disable it BEFORE driving off with the goods! Or, pull power.

Depends on which part of the country you're located. Here, wooden-framed homes are an exception. I've never encountered a home with a basement. Attic spaces are solely to decorate the "elevation" (roof pitch is too low due to lack of snow carrying requirement).

Some adobe and straw-bale homes have walls 18" thick.

Stucco over masonry, here. Stucco over lath over wood for framed portions of homes (e.g., exterior wet walls).

Or, part them out before they can be found.

Here, a stolen car is in MX in less than an hour. Even cars that have been legitimately *sold* may never see a formal title transfer (e.g., if the buyer intends to use it in a crime; think smuggling).

and SOLUTION! :>

Dunno. As I said elsewhere, *I* don't use cellular comms. The *cordless* phones work everywhere in the house so we have no problem. But, friends and neighbors seem to resort to "stepping outside" when they have to make a call of any duration.

I suspect they must keep their phones located "in a sweet spot" indoors lest they miss calls/texts (?). Or, resort to post-processing calls by checking their voicemail (apparently, calls are intercepted thusly in relatively short order... do they have to "run" to answer the phone sited in that "sweet spot"? -- we have "extensions" throughout the house)

I suspect it will have to be addressed by siting the antenna in a "good location", much like the OTA services (which folks may or may not use). I'm replacing it with an SDR so I can handle several different comm needs with a single radio. E.g., I only need a "time update" every month or two as I discipline my local "wall clock" with the AC mains. And, most folks don't worry about the accuracy of time to anything finer-grained than "a couple of minutes" -- largely because they are at the mercy of other folks' notion of "current time" in most interactions! If your boss thinks it's 8:03 when you show up for that 8:00 meeting, it doesn't matter if you pull out your cesium reference and "prove" to him that it's really 7:59 -- he'll still consider you late (and a wise-ass to boot!) Likewise, the airline decides when the 9:00 flight departs.

[You only need better accuracy if you *know* -- e.g., contractually -- what reference the other party will be relying upon. And, need finer-grained synchronization only if the parties that must agree on a common time require such. E.g., most computer networks are fine with 1 second or worse as different machines are rarely needing to share a notion of time beyond what their users expect (the file server imposes its notion of "now" when you access/create one of its resources, regardless of what time YOU -- or your computer -- think it may be!) OTOH, if you have multiple SEPARATE processors working on a common problem, then tighter synchronization may be required -- if only to order observations and actions in time (A did something at A's notion of time and B did something at B's notion of time; which came first? Especially as processors get faster)]

So, check the time at some "idle" time of day/night. Use the SDR for other purposes at other times (listening for pagers, door openers, broadcast radio, etc.)

The main thing is the ease of getting huge intercepted areas with a single pair of wires (i.e. one port), and a contributing thing is the energy per photon.

The etendue (area*solid angle product) of a single electromagnetic mode is

E = lambda**2 / 2.

If you need more etendue than that, i.e. either a wider acceptance angle or more intercepted arear antenna's throughput is higher than that, you have to use either multiple ports or incoherent detection. The SNR tradeoff involved in going to much shorter wavelength is fairly heartbreaking.

Cheers

Phil Hobbs

uh, these homes lack windows? Last I heard, glass is transparent for RF

Re "1. How to punch holes in <whatever> is attenuating the signal " These homes do not have windows? Last I heard, glass is transparent over a wide EM spectrum including RF... = RS

Not necessarily when it has a thin metal coating to reflect infra-red radiation. Such glass is mandatory for all new windows here.

John