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Safe Transmission Distance from GMS Interior Antenna

Safety Antenna Transmission

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#1 SnoopCoop

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Posted 28 July 2020 - 09:38 AM

Hello Great Forum:

 

I have an office in my Townhouse and cannot place an antenna outside.  I have a large picture window in my 2nd floor office which faces north and should be able to hit the Fort Pierce transmitters.  I want to place the Midland low profile (3db gain) antenna very close to the window on a round 15 inch tin pizza pan for ground plane. The blinds are plastic/vinyl so there is no metal in the way. Screen removed.   I want to place the Midland GMRS radio on my office desk which is by far the most convenient and available place.  

 

QUESTION:

I have read that 7 to 10 feet is a safe distance from a transmission and also read that the FCC mentions for HAM frequencies, evaluation of radio wave radiation concerns HAM RADIO frequencies over 50 watts.  I am anticipating the purchase of a Midland 15 watt or Midland 40 watt GMRS radio.  I would be about 7 feet away from this transmitting antenna when actually transmitting for short periods.  With the relatively low wattage does anyone have a learned opinion if this a health problem.   Would the difference beetween 15 and 40 watts really make a difference?  Think I am safe at 7 to 8 feet away?  At present... I am thinking I am.  Thoughts my knowledgable neighbors?



#2 aj22185

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Posted 28 July 2020 - 10:00 AM

Hey Snoop. Thanks for the advice on my post. This topic is a little more up my alley.

Speaking in general terms outside of GMRS:
The thing about electromagnetic energy (radio waves) is, it's literally everywhere already. Light, sound, RF, and even the more harmful X-ray and gamma ray energy are all propagating constantly all around us. For GMRS purposes the wavelengths are pretty long (2 meters ish) so the likelyhood of any harmful health effects are very slim even when standing very close to a high power transmitter. The main concern is much higher frequencies (several gigahertz such as those used for radar and higher) at very high outputs. The higher the frequency the more dangerous it becomes, and the same can be said for output power in those higher bands. There are many stories about sailors feeling physically warmer when standing in front of the high powered radar stations on naval ships. For this reason there are painted lines on the deck to help keep them safe. "Radiation" does not simply apply to all frequencies with regard to it's ability to alter cellular DNA. The frequencies required to do that have wavelengths that are incredibly small.

That's a long explanation, but think of it like this, if RF energy were that harmful would it be safe to hold a 2 GHz 0.5W transceiver (your cellphone) up to your head for hours at a time? While claims have been made that it causes health issues, they are largely unsubstantiated and most have been debunked.

All that to say, you'll be just fine using a UHF transceiver at 40W, or even 400W for that matter.

Sent from my SM-G965U using Tapatalk
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#3 axorlov

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Posted 28 July 2020 - 10:32 AM

Here is a simple calculator for RF exposure:

http://hintlink.com/power_density.htm

 

For 15W at 462MHz safe distance seem to be little more than 4ft. More info here:

https://transition.f...et65/oet65b.pdf


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#4 berkinet

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Posted 28 July 2020 - 10:39 AM

Two quick .comments. GMRS is closer to 64cm than 2meters (~144mHzj And, when considering signal strength and safety, keep in mind that the intensity of radio waves over distance, like light, obeys the inverse-square law, which states that intensity is inversly proportional to the square of the distance from the source. I.e. double the distance, and you get four times less power.
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#5 aj22185

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Posted 28 July 2020 - 02:24 PM

Two quick .comments. GMRS is closer to 64cm than 2meters (~144mHzj And, when considering signal strength and safety, keep in mind that the intensity of radio waves over distance, like light, obeys the inverse-square law, which states that intensity is inversly proportional to the square of the distance from the source. I.e. double the distance, and you get four times less power.

Thanks for the correction.



#6 SnoopCoop

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Posted 28 July 2020 - 02:49 PM

Thanks ALL!  It looks like I will be good to go and not much of a health hazard, if any, at about 7 feet away.  



#7 jdh

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Posted 28 July 2020 - 05:09 PM

Thanks ALL!  It looks like I will be good to go and not much of a health hazard, if any, at about 7 feet away.  

RF interference back into your radio unit or other office electronics might still be a concern even if the health issue is not. I seem to be having some issues like this with my attic-mounted antenna being maybe ~10 feet from my MXT400 with a wall and ceiling in between.



#8 SnoopCoop

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Posted 28 July 2020 - 05:33 PM

RF interference back into your radio unit or other office electronics might still be a concern even if the health issue is not. I seem to be having some issues like this with my attic-mounted antenna being maybe ~10 feet from my MXT400 with a wall and ceiling in between.

 

Yep!  I will definitely check my swr's but I am betting at this point.. not a problem. Thanks!!  I have a nearby ham friend who will allow me to borrow his swr meter.  Again. Thanks for the input by you and others.  



#9 wayoverthere

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Posted 28 July 2020 - 05:46 PM

RF interference back into your radio unit or other office electronics might still be a concern even if the health issue is not. I seem to be having some issues like this with my attic-mounted antenna being maybe ~10 feet from my MXT400 with a wall and ceiling in between.


I know the first time I keyed up the 50x1 with the mag mount antenna on top of the mini fridge by my desk, my printer (on the desk next to the fridge) woke up and printed a couple pages of gibberish
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#10 Elkhunter521

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Posted 29 July 2020 - 11:34 AM

Consider this comment as food for thought. I've noticed some interest in HT radios with higher tx wattage. As these are held occasionally as a phone, against one's head, how desirable is a 10 watt HT? Even held 6 to 8 inches from your mouth is 10 watts safe?

Be vewy vewy quiet.
I'm listening to my wadio!





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