[ale] Outdoor Wifi - Water - The missing Detail?
Alex Carver
agcarver+ale at acarver.net
Tue Jun 29 00:11:21 EDT 2021
The WiFi spectrum is not quite on top of the 2.4 GHz water absorption
band. However, 2.45 GHz was chosen as the ISM band (Industrial,
Scientific, Medical) because microwave ovens used it first and that's
simply because no one wanted it for other things (like TV and radio).
Later the FCC had to find some space for all the whiz-bang gadgets that
wanted a radio so up was born the ISM bands at 915 MHz, 2.4 GHz and 5 GHz.
There *IS* a water absorption band in the 5 GHz WiFi area which is why
it was available for ISM usage but it's not the reason for 5 GHz vs. 2.4
GHz WiFi. The attenuation is also much higher than 2.4 GHz so for
distance 2.4 GHz will win over 5 GHz on any rainy day. 5 GHz is also
lossy through other materials that are hygroscopic like gypsum/paper in
wall boards and concrete in brick walls. It's also scattered by surfaces
a lot more than 2.4 GHz so you get more possibilities for multi-path
interference.
The 5 GHz band was actually the first WiFi band (802.11a) but
implementers wanted something that could propagate longer distances so
WiFi moved down to 2.4 GHz (802.11b and then much later 802.11g, 802.11n
and a portion of 802.11ax) where the path loss was lower. 5 GHz came
back into popularity simply because 2.4 GHz is overloaded now. WiFi,
Bluetooth, ZigBee, random RF links, microwave ovens, and plenty of other
things all wanted a slice of ISM and there just isn't enough room in
2.40-2.50 GHz. Plus the total available bandwidth in 2.4 GHz ISM (100
MHz) is smaller than that of 5 GHz ISM (150 MHz) so if you want higher
WiFi throughput you have to go to the higher frequencies. (note that
WiFi doesn't get access to all that bandwidth either, just a slice).
So in comes 802.11p which adds a slice of spectrum to the top of the
WiFi 5 GHz band because 5 GHz is also now overloaded. Next up for the
US markets is 802.11ax that snags a whopping 1.2 GHz of bandwidth at the
top end of the 802.11a/n/ac going all the way to 7.125 GHz.
Water on its own is extremely absorbing, part of the reason why it's
pretty much a magical substance. Water ice is the only known solid that
floats in its own liquid which allowed life to survive on Earth during
the proposed Snowball Earth and other Ice Ages. If it behaved like other
chemicals, it would sink and Earth's oceans would have frozen solid
(this discounts Titan's methane oceans because the surface ice is a
blend of methane and ethane ices so it's slightly less dense than pure
methane ice which would sink).
Water is a highly polar molecule because it's "bent" which is what makes
it a very general purpose solvent and allows liquid biologic activity as
it can dissolve nearly all of the compounds required for life to thrive.
The bend and polarity are what give it the huge range of absorbing
frequencies from deep in the RF and infrared all the way up into high
energy photons like X-rays.
On 2021-06-28 17:34, Jon "maddog" Hall via Ale wrote:
> I am not an RF guy, but I do know that one of the differentiation points of 2.4 GHz versus 5 GHz is the absorption of 2.4 Ghz by water. This is *one* of the reasons why 2.4 GHz is a frequency that is free from other serious uses. It is the frequency used by Microwave ovens to cook food. So if you used 2.4 GHz for things other than cooking your food (like communications) you would get a lot of packets dropped while Johnny is cooking his hot dog.
>
> Apparently water molecules vibrate best at 2.4 GHz, and it is the vibration of the water molecules that creates the heat that cooks the food in a Microwave oven.
>
> Fortunately WiFi uses other techniques so it does not look too much like a cooking hot dog. Still, having your Microwave going during your use of WiFi will slow down your throughput.
>
> Likewise all the water in the leaves, rain, fog, etc. will be vibrating along, absorbing the waves.
>
> 2.4GHz also tends to be the frequency used by unlicensed radio control cars and planes, cheap walkie talkies, blah, blah, blah
>
> SOOOOOOO, use 5 Ghz.
>
> RF guys, you are welcome to tell me I am full of S*T and laugh at me.
>
> maddog
>
>> On 06/28/2021 1:17 PM Neal Rhodes via Ale <ale at ale.org> wrote:
>>
>>
>> It takes me a while sometimes. So, looking for "wifi loss through
>> trees", once finds comments which suggest that while wood might not
>> reduce Wifi, WATER does, and trees and leaves contain water.
>>
>> Well, people contain even more water.
>>
>> So, it's looking to me like a single directional access point at the
>> back of the building is doomed. It might look like it works, it might
>> even test pretty good. Empty.
>>
>> BUT, put a 60x130 tent in the back field, fill it with 800-1000 people,
>> put the beer and food lines at the back side, (because grills, beer
>> trailer, warmers, ice-trailer, etc are all on the back side, and put
>> volunteers running tablets at table-top level, then each tablet is
>> trying to get Wifi THROUGH about 40 people. Who are well-beered. Just
>> not going to work.
>>
>> Looks like we should indeed run a pair of somethings to get across the
>> parking lot, then Cat6 to the rear tree line, and then an access point
>> high up, so that food/beer staff have nothing between them and the
>> access point.
>>
>>
>>
>> On 2021-06-28 11:08, Neal Rhodes via Ale wrote:
>>> Thanks. Please, keep the ideas coming. There were comments about
>>> power - nope, no conduit, Scout building and rear tent power all come
>>> from separate lines back to the transformers on the pole.
>>>
>>> What I'm getting from the Ubiquiti forum is that UAP-AC-LR-US 802.11ac
>>> Long Range Access Point will likely peter out at 300 ft.
>>>
>>> Note that the satellite view is stale - the two trees right at the
>>> back of the church building are gone - they were sending roots towards
>>> the foundation. So, it's a clear shot up to the trees beyond the
>>> driveway. Unclear to me how much a couple of trees at that distance
>>> can block WiFi.
>>>
>>> Responses do suggest that we may have TWO distinct groups to cover or
>>> not: Vendors in the parking lot, and our beer/food vendors at the back
>>> of the tent. The parking lot may have to get tossed over the side as
>>> 2nd priority. Frankly, I think most of the vendors do other
>>> festivals, and have worked out how to do their credit cards on their
>>> phones; they would just rather not spend their data. I think cell
>>> coverage in the parking lot is adequate.
>>>
>>> So, if I understand your approach, it involves two NanoStations? Or
>>> two NanoStations to get from building to back field, and an access
>>> point on the field NanoStation to provide the Wifi to the tablets?
>>>
>>> regards,
>>>
>>> Neal
>>>
>>> On 2021-06-28 10:40, Alex Carver via Ale wrote:
>>>> Just to add fun to the festivities I have a couple of these
>>>> NanoStations
>>>> that work very well as PTP bridges:
>>>>
>>>> https://store.ui.com/collections/operator-airmax-and-ltu/products/nanostation-loco5ac
>>>>
>>>> The radiation pattern is more directional than the UFO-style AP's like
>>>> the UAP AC so it tends to work better for that purpose. They're also
>>>> able to work in a multi-drop configuration so you can have multiple
>>>> endpoints instead of cable. When they're in PTP mode they're not
>>>> directly accessible with normal WiFi products, the protocol is
>>>> different
>>>> so it's harder to have someone "tap" into your connection from a
>>>> sidelobe.
>>>>
>>>> They're also inexpensive at $50 each and rated for outdoor use.
>>>>
>>>> These should work at the range you're wanting but you can always go up
>>>> a
>>>> bit and get something like this if range really is an issue:
>>>>
>>>> https://store.ui.com/collections/operator-airmax-and-ltu/products/litebeam-5ac-long-range
>>>>
>>>> Built-in dish makes a tighter beam and a lot of range (like several
>>>> miles in unobstructed LOS).
>>>>
>>>> Many options in Ubiquiti's airMAX and airFiber device groups.
>>>>
>>>>
>>>> On 2021-06-26 09:12, Neal Rhodes via Ale wrote:
>>>>> Thanks to all that replied. My goal was to figure out the options,
>>>>> and
>>>>> focus some other people's attention in a productive direction. I do
>>>>> NOT want to be the expert on this, as on the day, I'm busy doing
>>>>> sound
>>>>> or playing music on stage.
>>>>>
>>>>> I will quickly summarize the high points I've passed on. Not to
>>>>> preclude further comments from the ALE group, which I value. But
>>>>> I'm
>>>>> gonna let this simmer and see if some other folks pick up the ball.
>>>>>
>>>>>
>>>>> WHAT IS THE ENVIRONMENT? You can look at Google Maps for 1826 Killian
>>>>> Hill road, Lilburn
>>>>> From back window to the far tree line at back of field: 450ft (137
>>>>> meters)
>>>>> From back window to the scout building: 170ft (52 meters)
>>>>> From scout building to back of field: 304ft (92meters)
>>>>> A straight line of Cat6e wire from back door, across the driveway on
>>>>> the
>>>>> choir room side, to the trees, then along the side of the property,
>>>>> back
>>>>> to the cross near the fire-pit: 500 ft ( 152 meters)
>>>>>
>>>>> So from Back wall of building to where the Beer is sold is 480ft.
>>>>>
>>>>> OPTIONS:
>>>>> A) Run a 500 foot Cat6e cable from the switch in the sanctuary, out
>>>>> the
>>>>> choir room fire escape, out the Choir fire escape door, across the
>>>>> driveway in a 1/2” PVC pipe, with pieces of 2x4 slant cut on either
>>>>> side to make a ramp to drive over, along the tree line, to the cross
>>>>> near the fire pit, and place an access point there. We would already
>>>>> have power there for audio speaker.
>>>>>
>>>>> B) Implement a Mesh network, using existing Virtual Studio Raspberry
>>>>> PI
>>>>> processors, from the back window, to the scout building, to a unit at
>>>>> the tent. While possible, this leaves one more essential component
>>>>> of
>>>>> Oktoberfest that Only Neal Understands.
>>>>>
>>>>> C) Place a purpose built long range Access point outside, perhaps on
>>>>> the
>>>>> classroom fire-escape wall, where it will be in the shade of the
>>>>> steps.
>>>>> This could be a permanent installation. Some of these can be
>>>>> powered
>>>>> by the CAT6 cable connection. (POE) Neal is not an expert. I am
>>>>> reading that some units claim coverage of up to 600 ft. This would
>>>>> include coverage of the rear parking lot.
>>>>>
>>>>>
>>>>> Possible products: This is by no means exhaustive; consider
>>>>> https://www.mbreviews.com/best-outdoor-wifi-range-extender/ for more
>>>>> details/ideas.
>>>>>
>>>>> A) Ubiquiti Networks UAP-AC-LR-US 802.11ac Long Range Access Point
>>>>> $109
>>>>> https://www.bhphotovideo.com/c/product/1189144-REG/ubiquiti_networks_uap_ac_lr_us_802_11ac_long_range.html
>>>>> There are indoor, and indoor/outdoor flavors of these. Some
>>>>> powered
>>>>> by POE.
>>>>>
>>>>> B) TP-LINK CPE210 N300 Outdoor Access Point $39
>>>>> https://www.microcenter.com/product/482831/tp-link-cpe210-n300-outdoor-access-point
>>>>> This unit appears to be designed to mount on an outside wall, and has
>>>>> directional antenna which focus the signal in one direction only.
>>>>>
>>>>> C) CPE510 5GHz 300Mbps 13dBi Outdoor $49
>>>>> CPEhttps://www.tp-link.com/us/business-networking/outdoor-radio/cpe510/
>>>>> Unclear what you get for the additional $10.
>>>>>
>>>>> Now that I'm writing this, I'm wondering if the TP-Link units really
>>>>> only work talking to each other, and not to a tablet out in the
>>>>> grass.
>>>>>
>>>>> regards,
>>>>>
>>>>> Neal
>>>>> _______________________________________________
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>>>>
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