RF Exposure limits?

ExKa|iBuR · Post by **ExKa|iBuR** » Sat Sep 25, 2004 10:43 pm

I was just wondering.

With respect to commercial FM broadcast stations, is there some kind of regulation as to how much stray RF can be present in the transmitter room?

I went up to the transmitter room at the CN Tower here in Toronto tonight where a few dozen commercial FM and Television, as well as any number of land-mobile transmitters are located. Within about 5 minutes of being in the area of all the multcouplers, filters and duplexers, my head felt like it was on fire and my fillings were aching really bad.

I'm pretty sensitive to RF as it is, but geeze, this one fellow had worked 8 hours up there before - that can't be safe!!

-Mike

Will · Post by **Will** » Sun Sep 26, 2004 1:02 pm

There is exposure limits here in the US that the FCC has set. The FCC has been actively checking the broadcast stations to make sure they comply, a lot of them did not and got heavyly fined.

Most exposure occurs near the antenna(s), and there must be warning signs and a way to keep persons away from the RF field. usally a fence.

For example, UHF 440 mhz repeater at 50 watts, no closer than thirty feet from the antenna. In a car the metal does shield you and the duty cycle is very small.

sglass · Post by **sglass** » Sun Sep 26, 2004 4:56 pm

ExKa|iBuR wrote: I went up to the transmitter room at the CN Tower here in Toronto tonight

-Mike

how in the hell did you get in there

ExKa|iBuR · Post by **ExKa|iBuR** » Sun Sep 26, 2004 5:50 pm

With an access card (legit).

Look here:

http://69.0.232.188/Images/cavities.jpg
Massive (size of a 55 gallon drum) cavities for the Broadcast FM stuff

http://69.0.232.188/Images/combiner.jpg
Combiner for all the multicoupled FM transmitters (a dozen or so)

http://69.0.232.188/Images/duplexers.jpg
All the land-mobile duplexers

http://69.0.232.188/Images/VE3TWR.jpg
The local Amateur Radio repeater!

-Mike

Alright, I don't know what's up with my server - but to view them, copy (DON'T CLICK!) the URL and paste it in a new browser window.

But yeah. It's not bad, just sucks being there for 8 hours with the RF, which is why I'd asked if it's safe - can't imagine I'd be having kids anytime soon after doing that.

VA3XDJ · Post by **VA3XDJ** » Sun Sep 26, 2004 5:56 pm

I can't see the pics.

Must've been a cool sight (or site hehe)

Tom in D.C. · Post by **Tom in D.C.** » Sun Sep 26, 2004 6:52 pm

ARRL has the exposure computations and formulas on their site.

All the US hams are supposed to have RF exposures figured out and available at their stations. I did it for my location down in Virginia and it's amazing how little power, like 35 watts into a 5DB gain antenna, it takes to get you into a marginal situation. More so when there's a condo loft bedroom right under the antenna! Some of the loft area is above the ground plane of the antenna as well, which also makes it worse.

I'd hate like hell to have to work in an area which was being hit by thousands of microvolts (and worse) of RF.

Will · Post by **Will** » Mon Sep 27, 2004 12:18 am

Love that Macoroni combiner.

That is a much better site than some I have been on.

One site had four FM transmitters at 50,000 watts each. And a bunch of commercial two way and a couple of ham repeaters. When I would leave the building I of course would turn off the hall way lights, but they would not go off. I even verified that the wall switch was working. That was one hell of a lot of RF. I am sure that site did not meet any RF exposure standards.

Flint Peak, North of Los Angeles between Glendale and Pasadena. 1991

ExKa|iBuR · Post by **ExKa|iBuR** » Mon Sep 27, 2004 12:38 am

Yep, same deal here...the light switches don't do anything!

Funny, it's the tallest tower in the world but yet my cellphone STILL doesn't have a signal. Go figure, eh?

-M

sglass · Post by **sglass** » Mon Sep 27, 2004 3:25 am

ExKa|iBuR wrote: Funny, it's the tallest tower in the world but yet my cellphone STILL doesn't have a signal. Go figure, eh?

-M

sprint huh

va3wxm · Post by **va3wxm** » Mon Sep 27, 2004 5:58 am

ExKa|iBuR wrote:Funny, it's the tallest tower in the world but yet my cellphone STILL doesn't have a signal. Go figure, eh?

-M

With all that RF floating around up there I'm surprised it didn't blow up in your hand!

Here's a link for some RF exposure information from Canadian regulations.

Cowthief · Post by **Cowthief** » Mon Sep 27, 2004 6:24 am

Hello.

There are people out there who will drive 7 alternators to charge a set of big truck batteries to run a bank of amplifiers, for CB?!
The RF field must be murder!
This is on the same level as the people who build car stereos so powerful that you need hearing protection.
http://www.cnn.com/2003/TECH/ptech/07/0 ... index.html
http://www.bigradios.com/shadow/6erscb.htm

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Mon Sep 27, 2004 9:33 am

Cowthief wrote:Hello.

There are people out there who will drive 7 alternators to charge a set of big truck batteries to run a bank of amplifiers, for CB?!
The RF field must be murder!
This is on the same level as the people who build car stereos so powerful that you need hearing protection.
http://www.cnn.com/2003/TECH/ptech/07/0 ... index.html
http://www.bigradios.com/shadow/6erscb.htm

That's CB Sexy

richyradio · Post by **richyradio** » Mon Sep 27, 2004 3:04 pm

...time for my Monday night posts...notice I only post on Mondays as I have to do xmtr/tower/antenna switching on Monday overnights (when work is done) at a rather large building situated in midtown manhattan that houses all the radio and tv stations...so this topic is pretty much up my alley...went to a few schools on it...it's not any particular level of rf that is bad- it's a matter of frequency, power and time exposed to the rf field....believe it or not, high band is the worst-(for me, the hi-V ch.7 thru 13...) sort of resonant w/ the human body they say...I always thought microwaves were the worst- not so... (however, standing next to a UHF antenna w/ 110 Kw feeding it is not good either)...generally, you wear a "radiation badge" made by either Narda or General Microwave...looks like a pager, the better ones you can diddle w/ the menu and make it do what is applicable to your enviroment....it damages you purely by heating...it's not ionizing radiation like nukes...you can go into a nasty rf field for a certain time in/ time out period without a suit...(which they actually sell on e-bay as bug suits from army surplus vendors- they're plentiful) a headache is the first sign you've got issues....here's my quick and dirty rf sensor: wear one of those neon bulb wall socket testers w/ the 6" wires hanging out the bottom...if it lights up, you're in extra deep sh*t!

Nand · Post by **Nand** » Mon Sep 27, 2004 3:29 pm

http://www.hc-sc.gc.ca/hecs-sesc/ccrpb/ ... 37/toc.htm

One section from the above…

http://www.hc-sc.gc.ca/hecs-sesc/ccrpb/ ... apter5.htm

Nand.

grinthock · Post by **grinthock** » Wed Sep 29, 2004 4:52 am

So the question is.....

Should I warn (or am I legally abliged to warn) visitors on my balcony that they may be exposed to RF? Is it dangerous me standing/sitting on the baclony as it's transmitting?

50W 2M, 35W 70cm, into 3 foot J-Pole...

va3wxm · Post by **va3wxm** » Wed Sep 29, 2004 5:04 am

Probably not legally obligated but would be a good idea to warn them. Also tell them not to touch the antenna tip when you're transmitting.

Or don't and let them "feel" the RF.

grinthock · Post by **grinthock** » Wed Sep 29, 2004 5:13 am

I've always told people who have never been on my balcony not to touch the radials, because it's running APRS. It may transmit at any time.

But I wouldn't think it's i'm exposing people (or myself) to high RF levels.

I do make a point of making sure the wife isn't standing on the balcony when i'm involved in long QSO's

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