Question Getting wifi signal into a Faraday cage

[KArt715]

Well, almost a faraday cage! I have an outdoor wifi AP that gives good coverage in our large garden. I also have a shepherds hut (basically a shed on wheels) covered with tin sheets in which I want to receive wifi but the tin sheets are blocking the signal. The hut is 'off-grid' and only has power from a leisure battery & solar PV so I'd like to avoid an active AP if possible. Because the hut is mobile (and I do move it throughout the year) a simple cat5e cable solution is not very practical. So, how to get a wifi signal inside the hut? I'm wondering if a passive solution based on two back-to-back aerials might work? ie an external aerial connected to an internal aerial via a short length of coax through the wall of the hut. I know there will be a signal loss but I have a pretty strong signal from my garden AP, which makes me think it might possibly work - though I'm really just guessing. Would I likely be wasting my time buying some bits to experiment with this idea or is it a non-starter? Or, any other suggestions for solving this problem. Thanks.

 

[bill001g]

If you have strong signal 2 antenna hooked back to back with a cable will work. Be sure to get the shortest cable that will work. Quality microwave coax cable is expensive.

It is not real hard to get most network type of electronics to run on solar/battery. Almost all use external power and dc voltage so a dc/dc voltage converter will work.

 

[KArt715]

The hut walls are about 4-inches thick, so 6-inches of coax should be sufficient. I can use a phone app to measure signal strength but don't really have a feel for the likely loss from a passive solution. Any idea about what signal loss I'd be looking at?

You're right about running some sort of active repeater/booster off the battery, and it might come to that, but I'd like to dismiss the passive option first - either because it's a complete non-starter or after some experimentation. Sounds like you're suggesting it could be worth some experiementation.

 

[kanewolf]

Well, almost a faraday cage! I have an outdoor wifi AP that gives good coverage in our large garden. I also have a shepherds hut (basically a shed on wheels) covered with tin sheets in which I want to receive wifi but the tin sheets are blocking the signal. The hut is 'off-grid' and only has power from a leisure battery & solar PV so I'd like to avoid an active AP if possible. Because the hut is mobile (and I do move it throughout the year) a simple cat5e cable solution is not very practical. So, how to get a wifi signal inside the hut? I'm wondering if a passive solution based on two back-to-back aerials might work? ie an external aerial connected to an internal aerial via a short length of coax through the wall of the hut. I know there will be a signal loss but I have a pretty strong signal from my garden AP, which makes me think it might possibly work - though I'm really just guessing. Would I likely be wasting my time buying some bits to experiment with this idea or is it a non-starter? Or, any other suggestions for solving this problem. Thanks.

I would make a test stand up before installing your passive hardware in the hut. Use cardboard, and foil or window screen. Put a WIFI camera or similar in the box and see if you can connect.

 

[KArt715]

No need to build a test stand when I've already got the hut. I only need to drill a single hole for the coax connecting two aerials, so no great impact on the hut if it all fails.

What I'm really trying to get a feel for is how much signal loss I can expect with a back-to-back aerial configuration so I can decide if it's worth buying the necessary kit to experiment.

 

[bill001g]

Although you can try to calculate this it is really complex. I remember a text book that had the formulas so I would think it is some place online.

I would just try it. Buy a couple 9db antenna used for routers and then find a short cable with rp-sma female connectors on both ends. At short length you can use LMR200 or maybe even lmr100. If you were going distance you want at least lmr400. It depends what you can find. male to female cables are very common and you could use a female-female coupler. It takes some searching to find this stuff cheap. Should be under $50 total.

 

[KArt715]

OK, update time.

I took Bill001g's advice and tried it, with some limited success.

Test set-up:
TP-Link outdoor 2.4GHz wifi AP
Shepherds hut positioned 25m away with no obstructions
Samsung A5 smartphone with 'Wifi Analyser' app for measuring signal strength.
'Back-to-back' antenna comprised of two 9dB 2.4GHz wifi antennas connected by a 0.5m SMA-to-SMA cable.

Obviously this is not exactly a calibrated 'test lab' set-up but I hoped it would be good enough for comparative measurements.
One issue was that the indicated signal strength did vary quite a bit, though it was just about stable enough for comparative measurements after getting a feel for how much the readings changed and over what timeframe. basically they seemed stable engough for 15-20 seconds or so.

My method of testing the effect of the antenna was to wait for a stable reading and then, without moving the phone, hold one of the antennas above the hut roof through the chimney opening (woodstove not yet fitted).

Indicated signal strengths:
outside of hut (25m from AP) = -62dBm +/- 2dBm
inside of hut (no antenna) = -72dBm +/- 1dBm
inside of hut with one antenna positioned above roof and internal antenna hanging down inside hut = 2-3dB improvement.

So, some slight improvement, which might give a bit more range when connecting to the AP, though I suspect that I'd have got the same improvement (maybe more) by simply replacing the two smallish antennas on the outdoor AP with the double-sized 9dB antennas. I couldn't try this because the AP antennas have RP SMAs and my purchased antennas have standard SMAs. I think I'll buy a couple of adapters and give it try.

Another possibility is to buy an RF amplifier module covering 2.4GHz and fit that inside the hut connected to an external antenna, though I was hoping to avoid a powered solution. But that can wait until I've finished fitting out the hut and permanently positioning it, which will probably be about 3x the distance from the AP than in these tests.

Anyway, a some fun and games on a sunny afternoon

 

[kanewolf]

You can run a powered outdoor AP with ethernet through the wall. Power everything by solar with battery.
And remember that hearing the distant WIFI is only have the battle. You also have to transmit back to it.

 

[KArt715]

Needing a two-way link is a good point - one that I thought about when considering a passive solution but overlooked in terms of an RF booster amp!

I'm probably getting a little ahead of myself as I don't actually know how poor the wifi reception will be when the hut is in its final position, so I think I should wait until then. The good news is that since installing the solar PV + battery in the hut, it's beginning to look like I have plenty of power to spare from the 100W panel - although it is summer (almost) and I'm still fitting out the hut so its regular power usage is still a little unknown, but I'm now more confident that a powered solution will be practical - in which case there are many options.

There's also the option to pursue longer distance coverage from the AP end of things. I've ordered some SMA adapters so I can try out the 9dB antennas on the AP. I'm confident that will help though have no idea if it will be enough. I've also seen small dishes for APs, but while that might be ok for just the hut it might reduce coverage in other parts of the garden.

At least I've not yet run out of things to try