Will 25w Fry My Brain?

[Tandom]

First Post Ever! (Please excuse me if this is in the wrong place)

Finally received my GMRS call sign. With that, a nice 25w Lexien VV-898BP radio with the included Nagoya NL-R2 15" dual band antenna. Thing works like a charm on Simplex. From my apartment in Vernon, CT, there is only one repeater I can hit, the Enfield EmComm in Enfield, CT. My radio sits in the window at my 2nd story apartment, facing SSW. (Sadly all my windows face the same direction, and I cant put anything on the roof or outside.) From my location, the Enfield EmComm repeater is roughly 13 miles away, in the North direction. I'm still surprised my radio even reached Enfield, since its inside a brick and steel building, in a window facing almost the opposite direction of the repeater.

Regardless, I want more, and more for the future. The Nagoya included with the radio was ok, but I wanted something with a little more bite, and something I can take out camping or to events. I picked up a 462MHz rated copper J-Pole antenna from jpole-antenna.com, along with some nice LMR-400 jumper and PL-259 connections. Feelin good! Was wondering though.. what would the effects be if I keep using my 25w unit in my apartment? Currently Im using the Nagoya, which is pretty much a whole foot away from my face when I TX. But at 25w, and within a foot, are there any RF dangers? My apartment is roughly 700 sq ft, so I cant really put the new antenna with cable in another room. Living room bay window is probably the best place for it.

Once I start using the J-pole, Ill be a bit farther away from the actual radiation point, but only by a few feet or maybe a few yards. Will 25w fry my brains? Any advice for a 2nd story apartment dweller facing SSW?

Thank you all!
WQWU622

 

[cmdrwill]

That radio/antenna combination exceeds the RF Exposure regulations. And YES you can "fry your brain".

 

[nd5y]

https://www.fcc.gov/general/radio-frequency-safety-0
Enter parameters - Power Density Calculator - VP9KF/Hintlink
25 watts of RF at 460 MHz is not going to fry your brain or anything else from a couple feet away.

 

[Tandom]

That radio/antenna combination exceeds the RF Exposure regulations. And YES you can "fry your brain".

That makes me wonder then. Why would they manufacture a radio with the antenna so darn close to the head of the operator? I cant forget, this thing was meant for a backpack, so the antenna would be pretty darn close to the operators body, regardless.

 

[pinballwiz86]

https://www.fcc.gov/general/radio-frequency-safety-0
Enter parameters - Power Density Calculator - VP9KF/Hintlink
25 watts of RF at 460 MHz is not going to fry your brain or anything else from a couple feet away.

I would NOT transmit 25 watts on GMRS frequencies a couple feet from my body. It won't fry my brain but it will heat up body tissues. OP, if you can, at least mount the radio and antenna higher than the top of your head.

 

[SCPD]

Welcome to the wonderful world of radio, Tandom....
Your's is a good question... Now, do you want a simple answer or the physics lecture (laffing... ?

I say this seriously, because the biophysics of RF and the human body is very complex-- frequency, distance from the radiator, exposure time- to name a few parameters.

I have not kept up with the latest figures, but i will quote you the science I know from several years ago, published by the American National Standards Institute. They are affiliated with the IEEE (Institute of Electrical and Electronic Engineers)-- well, enuff bona-fid's, if you can trust anyone's number it is these people.
There are E fields and H fields (electric and magnetic)-- and their safety exposure rates vary depending on frequency.... Am I loosing you?... Sorry-- it does get involved. But that is what I want to convey-- The ANSI standard - is a maximum E field between 30 and 300 mhz of 1mW/cm squared--- for a controlled environment, but drops to 0.2 mW in an uncontrolled environment. There are different standards for H fields.
What I am getting at is, you are not likely to measure any of these fields yourself, and for a 25 watt station, you could indeed be "cookng your brain," then again you probably aren't. Always play it play it safe, but a 25 watt UHF radio is a pretty safe item.

I work around some really nasty! high power transmiiters, the ones that can cook you, literally. So, from Coyote's Rule's of Thumb , UHF radiators-- "Your head; a minimum of 20 inches (that's right, inches, not feet) from the base of any 400 mhz antenna at 25 watts (or less)". Above that?.. move away from that source (you can get away with higher densities at lower frequencies, but watch out when it comes to the microwaves-- you skull has a nice resonate frequency that will ring when you hit that certain note (leave us say 'Cel'Fones?')

Enjoy your new radio, get an outside antenna some day, and in the meantime don't operate with your antenna closer than 2 feet from your body.

.................................CF

 

[nd5y]

I would NOT transmit 25 watts on GMRS frequencies a couple feet from my body. It won't fry my brain but it will heat up body tissues.

If your'e afraid of being exposed to 25 W from 2 feet then you shouldn't use a hand held radio 6 in. from your head or less than that if belt worn.
Look up the Inverse-Square Law.

According to the calculator I linked to:
462 MHz 25 W into a 3 dBi gain antenna at 2 feet the power density would be 2.7346 mW/cm2.

That's assuming that the attached antenna is a 5/8 wave and really has that much gain without any kind of ground plane.

If you change that to 4 W with 0 dB gain antenna at 6 inches away the power density would be 3.5085 mW/cm2 wich is way more because it's 4x closer and doesn't account for the fact that a typical hand held antenna is probably -6 dBi or less but the calculator won't take negative gain figures.

 

[N4GIX]

Looking at the certification for that radio,

The antenna(s) used for this transmitter must be installed to provide a separation distance of at least 90cm from all persons and must not exceed an antenna gain of 0dBi.

30cm = 35.4331 inches

 

[paulears]

I tend to think similarly to Tom, and don't forget that aerials are not point sources devices, yet we calculate them as if they are - but if the power is distributed along the length of the antenna, then the actual field strength is probable;y even lower.

This is one of those things you have to sort out for yourself, because RF damage to human tissue is thankfully rare. It's also got a time function in the calculation. Exposure time as well as strength.Would I hold an aerial connected to a functioning UHF transmitter running 25W? Yes, probably I would. 50W, and I think I'd start to take sensible precautions. 100W, and I'd not want to get close, and at full legal limit for ham UHF, I'd not want to be close for very long at all. Above 1GHz, I start to get a bit concerned with aerials with gain, and more than very low power.

The inverse square law was mentioned. About twenty years ago, people were panicking about microwave ovens leaking, so I did a test. I took a frozen pea and put it across the room from the microwave. I jammed a small dwell into the safety release on the door so I could turn it on remotely (one of those mechanical timers). With the door open and a 10 ft distance, nothing happened to the pea after 5 minutes of door open working. The 600W oven had to have the pea closer than just over 18" away from the oven for there to be any sign of the pea melting, and that still took a while. Try the frozen pea test by putting one next to your aerial and see if the ice melts.

 

[Tandom]

They are affiliated with the IEEE (Institute of Electrical and Electronic Engineers)-- well, enuff bona-fid's, if you can trust anyone's number it is these people.
There are E fields and H fields (electric and magnetic)-- and their safety exposure rates vary depending on frequency.... Am I loosing you?... Sorry-- it does get involved. But that is what I want to convey-- The ANSI standard - is a maximum E field between 30 and 300 mhz of 1mW/cm squared--- for a controlled environment, but drops to 0.2 mW in an uncontrolled environment. There are different standards for H fields.
What I am getting at is, you are not likely to measure any of these fields yourself, and for a 25 watt station, you could indeed be "cookng your brain," then again you probably aren't. Always play it play it safe, but a 25 watt UHF radio is a pretty safe item.

I understand. And I know my posting history and profile are new, but I've been playing with radios since I was 5. At some point I had to learn the math to progress. Hopefully I have something to offer back to this community Anyone want CB help? Lol

But seriously, I wasn't to worried about literally "Frying brains", but I was worried about prolonged exposure over time, in an enclosed room. I can put the antenna in the bay window, and run a jumper to the other side of the room and TX from there. That would be at least 12 or 15 feet-ish. Not worried much, but wanted to be sure.

 

[Tandom]

Try the frozen pea test by putting one next to your aerial and see if the ice melts.

As much as I would enjoy microwaving my frozen veggies, I'm not to convinsed my 25 watts would warm a frozen pea from the distance I would comfortably operate. I did get a kick out of your experiment. Brings me back to the days when I was running verious tests on opjects that would influence the standing wave radio of my old aerial .

 

[SCPD]

(I am smiling as I recount this---

We would get frequent VIP visitors to my lab and since they often represented funding for some new toy, I liked to put a bit of theatre into the tour.

We'd place a high powered 3cm pulsed magnetron- fed 33db horn pointed at a bunch of hot dogs on a plate, along side a Pyrex coffee pot - all at considerable distance across the lab.
The magnetron was turned on, and Presto, lunch was served! (Well, not exactly, we did feed our guests much better than microwaved hotdogs but many did taste them and thought it all quite instructive---- oh, BTW, no guest was permitted anywhere near that horn!)

........................... CF

 

[Hans13]

That's a reasonable and wise question to consider, Tandom. It's a question I asked myself when I first got the same model radio. For my own peace of mind, I make sure there is a few feet between my head and the antenna. I don't really believe that it would cause any damage but I figured it couldn't be too healthy in the long term to have it right up near my head. So, I sit a normal distance away from the transmitting antenna. I also try to use earbuds or speakerphone on my cell phone if I'm going to be using it a lot. Again, it's more peace of mind than anything else.

By the way... If you ever notice that the receive light is on but squelch doesn't open for the speaker, turn off power save and power cycle the radio. A buddy of mine figured that out when we were having said issue. It only seems to happen every now and then with weak signals. The only way to get it out of that state was to press a button and, presumably, wake up the radio. We leave power save off because that minor issue.

 

[Tandom]

the receive light is on but squelch doesn't open for the speaker, turn off power save and power cycle the radio. A buddy of mine figured that out when we were having said issue. It only seems to happen every now and then with weak signals. The only way to get it out of that state was to press a button and, presumably, wake up the radio. We leave power save off because that minor issue.

YES! I keep forgetting to mention that minor annoyance. Thank you! Was scratching my head going "there's action, but I can't hear anything!"

 

[Tandom]

All in all

Thank you all for the wonderful input on my first thread. From what I've gathered, I'll simply keep my body away from the antenna. Kinda stinks how short the mic is. Its a standard length, but if I pull it, unless the radio is propped somehow, it will topple over. My original fix for this is the connections and jumpers I ordered. Once those arrive, and the new copper J-pole ship in, I'll be able to TX, much better then I do now, and all without frying my brains. Thank you!

 

[Hans13]

I'm thinking about making some legs to fit on the bottom to keep it from falling over. I've also considered making a longer microphone lead. Lastly, I've used a right angle connector for the antenna connector and four medium sized round non-skid adhesive feet on the bottom that I picked up at Lowe's for about four or five bucks.

 

[Tandom]

I remember back when the PlayStation 2 came out, Sony released "legs" for it because it was kinda thin and fell over alot. All it was was an advanced vertical base. I kinda want to use the same system. Google "Fat PS2 Vertical Stand" and you'll see what I mean.

Also, I was wondering how hard it would be to make an extended mic lead. Shouldn't be to hard.

 

[bharvey2]

A lot of good information here. While you aren't likely to "fry your brains" in just a few minutes, long term exposure is a bit more questionable and I wouldn't want to spend a significant amount of time in the presence of an antenna radiating 25W. You might consider getting a small yagi and sticking it on a pole out your window. even a few feet increase in distance will significantly reduce your exposure. The yagi will further reduce the amount of RF radiating in your direction. Either that or get an RF "bunny suit" and impress your friends!

 

[paulears]

I have to admit to being a bit negative to the potential risks, as they're based on .... well, I don't really know who found these 'safe' limits in the first place, and the safe dose will change every year for a long time - but it did occur to me that some of the newcomers posts about why then they hand-hold a radio, the results seem very variable? Asking why as they turn their body, people can't hear them? The RF must be being absorbed by something - and the answer of course is the person's body. So we accept as total fact that RF can't go through bodies very well, but nobody seems to twig that that means it has to be doing something - and the obvious answer is warming up their tissues!

 

[SCPD]

Tissue penetration is dependent on a number of factors, but most RF will only go a few millimetre's deep-- this is a very apt application of the term "skin effect"...literally. Heat up the tissues?, you can bet it will! but unless it is high energy photons--Ionizing radiation ( "x-rays") RF can be considered quite harmless---in small amounts! Exposure time, frequency, all all are in the mix--( think: popcorn in a microwave oven v.s. your 1 watt handheld.....

..........................CF