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Author Topic: Wireless hub positioning  (Read 1416 times)

jelv

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Wireless hub positioning
« on: April 04, 2017, 04:21:04 PM »

This question was posed on the Plusnet forums:

Quote
I heard that it is better to have your router/Wifi so that the signal can "drop/spread from above" (i.e. upper floor) rather than have it downstairs so the signal has to "rise".....is that true?

An answer given was:

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In theory, the signal will radiate at 0 all around the router. In practice, it will always be angled upwards to a greater or lesser degree, depending on the frequency and proximity to ground level. It will certainly not 'drop from above'.
Better therefore, in a two storey house, for the router to be on the ground floor.

I've never heard this one before - any truth in it?
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Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning. Rick Cook, The Wizardry Compiled

Iain

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Re: Wireless hub positioning
« Reply #1 on: April 04, 2017, 05:08:00 PM »

I think he missed the 36 in front of the 0 !

Of course much will depend on the shape, and even direction of the antenna. Not much you can do with the standard router types.
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j0hn

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Re: Wireless hub positioning
« Reply #2 on: April 04, 2017, 07:13:23 PM »

With routers like my Asus RT-AC68U with external aerials pointing up, I would place the device on the ground floor. I see no reason why a signal would "drop" easier than it would "rise". There's no mass to drag it down, the signal should radiate in all directions.

With my router I imagine the signal radiating out evenly apart from straight down as the main body of the device is directly beneath the aerials. This would surely have some impact on the signal if you were directly beneath it.

For a router with no aerials it would depend where in the device the internal aerials were positioned.
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Weaver

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Re: Wireless hub positioning
« Reply #3 on: April 04, 2017, 08:41:24 PM »

I think that is highly dubious 'certainly not drop from above' given that many wireless access points such as my Cisco units for example are specifically designed for ceiling mounting. It all depends on the design of the unit and where the aerials are in relation to other metal if any in the device. If there is no other metal then all depends on the orientation of the units. And you can always mount a device on the ceiling upside down if you wish so that proves that all devices can drop from above. Am I correct?
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aesmith

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Re: Wireless hub positioning
« Reply #4 on: April 06, 2017, 01:12:04 PM »

Any antenna with a gain above 0dB by definition doesn't have a fully spherical coverage.  The so-called Omnis generally radiate 360 degrees with a dead zone where the antenna is pointed and in the opposite direction (an aside, radio control sets using 2.4 specifically shouldn't have the antenna pointing to the model).
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JGO

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Re: Wireless hub positioning
« Reply #5 on: April 06, 2017, 01:29:40 PM »

An aerial will normally tend to radiate upward due to earth reflection, but this is only predictable over a flat earth.

Inside a house there is still a solid earth underneath ( cellars excepted) but the upward direction will tend to be complicated by house structure so it is a rough guide  If trying to work with an aerial above the reception area I would be inclined to try a sheet of Ali foil above the aerial to provide a better defined ceiling. 
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aesmith

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Re: Wireless hub positioning
« Reply #6 on: April 06, 2017, 03:59:16 PM »

... If trying to work with an aerial above the reception area I would be inclined to try a sheet of Ali foil above the aerial to provide a better defined ceiling.
I've never ever seen that done, and there must be zillions of ceiling mounted APs, as already noted it's pretty much standard in office space.   Also, although I would be interested to see a reference if I'm wrong, I can't believe you really want to be receiving reflected signal as well as direct.  Isn't that asking for multipath errors?
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Weaver

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Re: Wireless hub positioning
« Reply #7 on: April 06, 2017, 04:18:11 PM »

Mind you modern kit likes multipath nowadays? Worth a try for a basic doubling of the energy +/- phase cancellation. I would expect it to be very channel dependent because of the phase difference surely?
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JGO

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Re: Wireless hub positioning
« Reply #8 on: April 06, 2017, 04:49:32 PM »

If you plug in some numbers the "multipath delay" is of the order of  a wavelength at the WiFi frequency, i.e. a tiny fraction of a degree at the modulation frequencies. I doubt if you could avoid it anyway. BUT I'm applying experience of electronics to computers -  Shock Horror !!

 
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aesmith

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Re: Wireless hub positioning
« Reply #9 on: April 06, 2017, 06:14:35 PM »

I'll see if we can test next time we're doing a wireless survey.  Although it begs the question as to why they're never deployed.
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JGO

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Re: Wireless hub positioning
« Reply #10 on: April 06, 2017, 07:07:02 PM »

I'll see if we can test next time we're doing a wireless survey.  Although it begs the question as to why they're never deployed.

The Great British " wecantdothatweveneverdoneitbefore" !     
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Weaver

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Re: Wireless hub positioning
« Reply #11 on: April 06, 2017, 09:58:40 PM »

Many years ago when I was working on RF networking, I always used to put a big biscuit tin lid underneath an antenna, or failing that, I'd find a large filing cabinet.
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sevenlayermuddle

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Re: Wireless hub positioning
« Reply #12 on: April 06, 2017, 10:52:20 PM »

I'm reminded of my first cordless phone, mid 1980s.   

These had a downlink just below the medium waveband, about 1.7 Mhz, radiated from the base station by a trailing wire antenna and picked up in the handset by a ferrite rod.   The uplink, about 50MHz iirc, was by a short telescopic antenna in both handset and base station.   The limiting factor affecting range always seemed to be the low frequency downlink.

I wanted mine to work at the pub about 200yds up the road, way beyond its normal capability.  But by loosely winding the base station's trailing antenna wire around the BT phone line, enough RF seemed to be coupled that the BT lines served to distribute the signal all along the road, and I could make and receive calls from the pub.   That was pretty cool, pre mobiles, early 80s. :cool:

Not entirely sure how legal or illegal it was, and not sure how many neighbours got my phone calls breaking through on their HIFis, privacy wasn't something we worried about then.   :)
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aesmith

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Re: Wireless hub positioning
« Reply #13 on: April 07, 2017, 04:44:20 PM »

The Great British " wecantdothatweveneverdoneitbefore" !   

Ha ha, guilty as charged I guess.  In truth in a reseller environment there are strong incentives to stick with the manufacturers' design and deployment recommendations, unless we are sure of the benefits. 

In practical terms it might be better for me to test at home.  Received signal strength at one end of the house, from an AP at the other end, is low enough that it should be possible to note whether there's any improvement.  What size reflector do you use, and how far behind the AP?   I need to do a baseline test first, but will probably try the AP upstairs against the wall so there's only lath and plaster immediately behind it (downstairs would be lath and plaster then granite so may already be reflecting).
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JGO

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Re: Wireless hub positioning
« Reply #14 on: April 07, 2017, 05:23:22 PM »

There isn't much practical data on restricted size reflectors 'cos we are talking about a  ground plane, i.e. in theory infinite in extent. BUT as you are not interested in the (usually low) radiation nearly parallel to ground, suggest as a starting point the HF/VHF Ground Plane aerial which gets by with 3 or 4 straight wires  each a quarter wave long.  At WiFi wavelengths of 12.5 cm or less a solid sheet at least this diameter  is practicable and should direct the radiation into to a cone round the aerial proper.   I'm talking in terms of lower frequencies where the aim is lobes inclined upwards - for this application just turn the whole system upside down .

A practical point on WiFi - the "earth" often seems to be connected by guess and by God - possibly back down the outside of co-ax to the metalwork of the cabinet ?!!!!     
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