Proximity to RF

[Extreme]

Asking for a friend, actually a guy on an ATV forum who's installed a dual band UHF/VHF 25 watt radio.

 

How close is too close to the head for an antenna?  I'm sure it depends on how often and how long signals are transmitted but from the looks of his photo the antenna and ball will be within a foot of the back of his head.

 

I don't wanna be 'that guy' and bark at him but considering a suggestion.  Thought maybe you guys would have something for me.

I checked FCC and it's pretty vague, or at best hard to get down to the numbers.

 

Thanks.,

[Radioguy7268]

Disclosure:

I'm not a lawyer, I'm not an engineer, and I'm not the one installing the radio.

 

Tell him to search up the "Inverse square Law" along with SAR - "Specific Absorption Rates".

 

This would also be a reason NOT to use cheap dual band radios without any FCC Type Certification (or worse yet, sketchy spec's at really odd power levels below what anyone actually uses).

 

Long answer short, the further away you get from the antenna, the less RF energy you'll have going through your head. The amount of transmit power that you're pushing, as well as the given wavelength of the frequency you're dealing with, will also impact the amount of energy your body absorbs. Having a roof, a helmet, or other obstruction will impact the amount of exposure. Dealing with a out of spec radio that's pushing energy into bands that it wasn't actually supposed to transmit on just adds a few more variables to the equation. Different antenna gain patterns can also impact the amount of energy directed in a specific direction.

 

Now that I've got  you worried, consider that 20 years ago, most Public Safety folks spent a significant part of their life less than 18 inches away from a roof mounted radio that pushed out more than 100 watts, and it didn't affect them too badly (cue all the Barney Fife comments). Also consider that the FCC themselves said that the best way to reduce the amount of energy from your cellular phone was to use it away from your body, by using either speaker phone mode or getting a hands-free accessory. Of course, now that just makes me wonder how much RF energy my Bluetooth headset adds back into the equation...

[Lscott]

Asking for a friend, actually a guy on an ATV forum who's installed a dual band UHF/VHF 25 watt radio.

 

How close is too close to the head for an antenna?  I'm sure it depends on how often and how long signals are transmitted but from the looks of his photo the antenna and ball will be within a foot of the back of his head.

 

I don't wanna be 'that guy' and bark at him but considering a suggestion.  Thought maybe you guys would have something for me.

I checked FCC and it's pretty vague, or at best hard to get down to the numbers.

 

Thanks.,

You want to look at something like the following:

 

https://transition.fcc.gov/bureaus/oet/info/documents/bulletins/oet65/oet65b.pdf

 

https://www.osha.gov/SLTC/radiofrequencyradiation/evaluation.html

[Ian]

Ham tech study guides go into this.

VHF is worse than UHF; the 30-300 MHz region is more strongly absorbed by meat than UHF.  Put it dead center on your car roof, or up on your house roof, or god help us a tower, and your exposure plummets.  Don't do the silly and use a 25 watt handheld, and you're probably capable of ignoring RF hazards unless you try to lick a transmit antenna, the power levels we operate at.

You don't have to get your ham ticket, but they've got some really good study guides that answer this question.

 

Edit:  Barney Fife is smarter than he sounds, he's just shrill and annoying.  Listen for his literary references, he's quite well read.  High INT, medium-low WIS, lower CHA.