Upcoming Maintenance Alert:

The UBNT Community will be upgraded at 5pm MDT on April 25th. During this time the community forums will be set to read-only status.

Learn more

×
Reply
New Member
Posts: 3
Registered: ‎09-06-2016
Accepted Solution

Question about AirFiber 5 RF radiation

I've searched, but haven't found anything about this subject on the forum.

 

Cell tower companies are usually over-the-top paronoid about RF radiation danger, with warning signs on the fences and requirements for RF education certification for climbers.  The certification classes basically boil down to, "Don't stand in front of the transmitter while it is powered up".

 

So with AirFiber 5 equipment, is there any danger to a person standing in front of a fully powered up unit?  How about personnel standing just below and in front of the unit?.


Accepted Solutions
SuperUser
Posts: 10,888
Registered: ‎12-08-2008
Kudos: 7694
Solutions: 481
Contributions: 1

Re: Question about AirFiber 5 RF radiation

[ Edited ]

No.   The EIRP is not a valid number for human radiation exposure numbers - the Tx power is still the Tx power, and that's the absolute maximim RF radiation that can ever come out of the radio + antenna.   Watts don't magically get generated by antenna gain.

 

And the absolute maximum conducted power from any AirFiber device is under four tenths of a watt.   Which could damage your eyes if it was 100% focused on your eyeball for a very long time, but coming out of the dish it's already spread across the entire dish aperture.  So there's no danger there.   And on a tower it's usually almst impossible to actually get in front of the dish, unless you were hanging on a long rope in front of it, which you should not ever do...

 

A lot of this is in reaction to unfounded fear of the idea of "radiation" - sounds scary, so watch out!   In reality unless the transmitter is in the multi-hundred watt range or more you're fine.  Again conducted power, not EIRP so please no-one start i with the " but my AF5X says it's putting out 54dBm, and that's like almost 250 watts!" because while that's technically true in comparison to an isotropic radiator, it's like sayig you can build a death-ray by shining a flashlight into a telescope - you still can't get more power out than you put in, period.   Otherwise we'd all be flying our own jet planes powered by single D-cell batteries...

 

Anyway in my younger days when I did a lot of tower climbing and built Radio and TV stations for a living, I was around 25,000 watt FM transmitters and the like, and when you are near the antenna (like within 10 feet or so) you can feel the heat in your skin from the RF warming your tissues, but even then as long as you're not dumb enough to touch the radiator you're not going to see any real damage.   I worked near operating FM and TV antennas many times and I suffered zero harm from them - that was 40 years ago, so I'd see some effects by now.   A lot of those warning signs and things are Lawyers doing Lawyer things because of Litigation, like the widow of one engineer on the Empire State Building who sued everyone in sight claiming her husband got cancer from years of exposure to the RF from all the antennas there.  She lost, BTW...

Jim

" How can anyone trust Scientists? If new evidence comes along, they change their minds! " Politician's joke (sort of...)

"Humans are allergic to change..They love to say, ‘We’ve always done it this way.’ I try to fight that. "Admiral Grace Hopper, USN, Computer Scientist

View solution in original post


All Replies
Emerging Member
Posts: 95
Registered: ‎03-26-2012
Kudos: 8
Solutions: 1

Re: Question about AirFiber 5 RF radiation

Depends on the eirp,
If your power with 55dbm (315W), i dont whant to stand in Front of the Antenna ,
With our 36dbm (4W) here in Germany i am not angry, my cellphone is allowed to do 2W an i hold It on My Head.
SuperUser
Posts: 10,888
Registered: ‎12-08-2008
Kudos: 7694
Solutions: 481
Contributions: 1

Re: Question about AirFiber 5 RF radiation

[ Edited ]

No.   The EIRP is not a valid number for human radiation exposure numbers - the Tx power is still the Tx power, and that's the absolute maximim RF radiation that can ever come out of the radio + antenna.   Watts don't magically get generated by antenna gain.

 

And the absolute maximum conducted power from any AirFiber device is under four tenths of a watt.   Which could damage your eyes if it was 100% focused on your eyeball for a very long time, but coming out of the dish it's already spread across the entire dish aperture.  So there's no danger there.   And on a tower it's usually almst impossible to actually get in front of the dish, unless you were hanging on a long rope in front of it, which you should not ever do...

 

A lot of this is in reaction to unfounded fear of the idea of "radiation" - sounds scary, so watch out!   In reality unless the transmitter is in the multi-hundred watt range or more you're fine.  Again conducted power, not EIRP so please no-one start i with the " but my AF5X says it's putting out 54dBm, and that's like almost 250 watts!" because while that's technically true in comparison to an isotropic radiator, it's like sayig you can build a death-ray by shining a flashlight into a telescope - you still can't get more power out than you put in, period.   Otherwise we'd all be flying our own jet planes powered by single D-cell batteries...

 

Anyway in my younger days when I did a lot of tower climbing and built Radio and TV stations for a living, I was around 25,000 watt FM transmitters and the like, and when you are near the antenna (like within 10 feet or so) you can feel the heat in your skin from the RF warming your tissues, but even then as long as you're not dumb enough to touch the radiator you're not going to see any real damage.   I worked near operating FM and TV antennas many times and I suffered zero harm from them - that was 40 years ago, so I'd see some effects by now.   A lot of those warning signs and things are Lawyers doing Lawyer things because of Litigation, like the widow of one engineer on the Empire State Building who sued everyone in sight claiming her husband got cancer from years of exposure to the RF from all the antennas there.  She lost, BTW...

Jim

" How can anyone trust Scientists? If new evidence comes along, they change their minds! " Politician's joke (sort of...)

"Humans are allergic to change..They love to say, ‘We’ve always done it this way.’ I try to fight that. "Admiral Grace Hopper, USN, Computer Scientist
Ubiquiti Employee
Posts: 7,077
Registered: ‎10-25-2011
Kudos: 1600
Solutions: 448
Contributions: 156

Re: Question about AirFiber 5 RF radiation

Hi @AYFHelpDesk

As eejimm says airFiber Tx Power is extremely low, even at full power in the worst case maximum Tx Power is 24dBm = 0.25 Watts.

 

Usually, those Radiation warning labels are for FM or TV transmitters, where Tx Power is measured in thousands of Watts.

 

Thanks,

¿Hablas español? Conoce nuestro foro de Ubiquiti en español - usamos la Ñ!
Highlighted
New Member
Posts: 3
Registered: ‎09-06-2016

Re: Question about AirFiber 5 RF radiation

Thank you for the informative and timely replies.

Member
Posts: 277
Registered: ‎11-19-2012
Kudos: 109
Solutions: 2

Re: Question about AirFiber 5 RF radiation

[ Edited ]

@eejimm that's the best explanation I've ever read - you've educated me. Thanks! I do wonder about your deathray anecdote though... we all remember burning holes in paper using the sun and a magnifying glass.. 

New Member
Posts: 29
Registered: ‎01-03-2017
Kudos: 2

Re: Question about AirFiber 5 RF radiation

@doc_karl The analogy is not quite correct. When it comes to a magnifying glass you are focusing the energy spread over the entire area of the magnifying glass in a single dot and if you make some math calculations you'll be surprised to realise that the area of the focused dot can be several hundred times smaller than the area of the magnifying glass. Even with a magnifying glass whatever you put in is what you take out, yet on a far less "square footage" so to speak and that "concentration" of energy makes your paper burn. Assuming that sun's radiation in watts is the same on each dot of the surface of the magnifying glass, the magnifying glass allows you to collect the individual energy of all those "dots" which comprises it's area and focus it/sum it up on a single dot which equals more watts per that particular dot that you focus on, while with RF the watts your radio puts out is the watts you're working with and in no way the antenna will convert that in more real watts. The EIRP which stands for "Equivalent" Isotropically Radiated Power tells you from start is not a real measurement in watts, so don't just convert the EIRP dbm in watts as those are not real watts. EIRP dbm is an "equivalent" of how many watts of power you should use to obtain the same effect without having the antenna gain. What burns your skin is not the "equivalent", but the real watts figure, which in our case is the Tx power expressed in watts and that value remains constant ierelevant of what antenna you use. The maximum Tx power in watts is a very low figure with all Ubiquiti radios and as a matter of fact with most tellecomunication radios, so don't worry, you won't be "fried" by a wireless communication device. @eejimm Could you confirm or eventually add to the above "non-scientifical" explanation. Thank you.

Member
Posts: 277
Registered: ‎11-19-2012
Kudos: 109
Solutions: 2

Re: Question about AirFiber 5 RF radiation

Yes I understand that cosminp, but at first look it's counterintuitive.... Banghead

 

Here's a better explanation..

 

https://www.quora.com/With-a-magnifying-glass-I-can-burn-paper-under-the-sunlight-but-not-under-the-...

Reply