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VHF coaxial radiation???

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monty0
1st Mate

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USA
51 Posts

Initially Posted - 04/27/2008 : 19:29:18

Hi,

A friend just looked at our boat and noticed that our VHF antenna was mounted on our stern pulpit. The radio set-up came with the boat. He was concerned about possible harmful radiation coming from the coaxial connector and how close people on the boat, esp. the cockpit, would be to the coaxial connector. He thought this might be an issue, but wasn't sure. In the army he drove jeeps with radio transmitting units on them and when transmitting they put a 25 ft barrier line around the jeep. He strongly recommended we look into getting a mast head antenna. We are headed to the San Juans in June. Any opinions out there on this topic?

Monty

1977 Catalina 25 #66 SRSK "Prana"

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 04/27/2008 : 19:53:09

Very little radiation should be coming out of the coax connector or the cable... the antenna radiates the signal.

There is some new evidence linking radio wave exposure (including cell phones) to increased levels of brain cancer... a 'definitive' judgement is still out. (One can appreciate that this topic is a hot potato).

IMHO: It wouldn't be a bad idea for a full power (20W) VHF antenna to be located well above the level of your body. Note that a 5W handheld is going to be radiating signal power very close to your brain. I don't worry that much about the handheld as I don't spend much time transmitting. If I was chatty on the radio, I might consider other options.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 04/27/2008 : 20:16:26

I agree with Bruce... The whole idea of the coax cable is to shield the interior conductor to preserve the signal for the antenna, where it is propagated. You're more than safe around the cable. And the only time your antenna is generating waves is when you key the mic, which presumably is infrequently. And 20 watts is barely enough to warm an ant inside a microwave oven. Don't sweat it. Cell phones are more problematic--they are transmitting periodically to let the cell towers know where they are.

Edited by - Dave Bristle on 04/27/2008 20:20:23

quilombo
Captain

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USA
301 Posts

Response Posted - 04/27/2008 : 21:24:36

ya kidding me right?

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 04/27/2008 : 21:30:45

About what?

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quilombo
Captain

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USA
301 Posts

Response Posted - 04/27/2008 : 22:01:23

sorry dave, I guess I was being a little sarcastic,,, lol, there are so many other sources of radiation all around us, that I just wouldnt consider the radio coaxial cable a problem,
but I suppose it was a valid question,

Edited by - on

Voyager
Master Marine Consultant

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USA
5445 Posts

Response Posted - 04/27/2008 : 22:26:56

RF radiation exposure has been a controversial subject for quite a while. In the early 90's we began to see articles written by consultants for radio and television stations who tested field strengths for a living. At that time, the Federal Communications Commission started commissioning testing for the effects of ionizing radiation on test animals. Conclusions have been very difficult to draw.

There are several key factors to consider with RF radiation:
1. Frequency - what wavelength or frequency is being used?
2. Power - how much RF power is being transmitted?
3. Proximity - the power at any point is inversely proportional to the inverse of the square of the distance from the transmitter, and
4. Exposure time.

By far, the most harmful types of radiation are those that can heat body cells. Microwaves, like the kind you get from microwave ovens around 2450 MHz happen to resonate with water molecules, and since we have so much water in our bodies, these can be harmful. Some satellite transmitters (not receivers) pump out tremendous amounts of power around this frequency, as do some "radar" detectors, the kinds used for foiling police speed radar.

VHF radios do not produce radiation with water heating capability. This is evidenced by the fact that VHF radios work as well in rain storms as on sunny days.

As I mentioned above, power is also important. Many VHF TV stations and FM radio stations pump out between 50,000 to 100,000 watts, versus 5 for handhelds and 20 for fixed mount VHFs. When these technicians have to work on these towers while they are powered on and transmitting, they put on special suits to vastly reduce the amount of power they are exposed to. RF engineers have only a slightly higher death rate than average people, and part of that comes from the risk of electrocution and falls from tall transmitters.

Proximity is important with handhelds and cell phones. The damned transmitter is right next to your brain! I like to use a wired handsfree device for this reason, especially if I talk for more than several minutes. VHF radios are similar. Using the formula, say you've got 5 W two inches from your head versus 20 watts 10 feet from your body:

5W at 2 inches: 1/(.16666)^2 ----> this is a factor of 36 x 5 ==> 180
20W at 10 feet: 1/(10)^2 -----> this is a factor of 1/100th x 20 ==> 0.5

The ratio is 180/.5 or 360 times.
So the power from your handheld is 360 times more power than the fixed mount ten feet away.

Exposure time. VHF radios expose you to radiation for brief periods - by law you are expected to transmit your warnings or questions in as brief a time period as possible on a VHF. Motor mouths are not tolerated on the radio. So exposure time is pretty low.

So, in judging mortality risks from VHF radios on the boat - limit your talk time. But all in all, your mortality risk is higher from sun exposure, fatty foods and smoking than it is from RF.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 04/27/2008 : 23:29:30

In addition to water heating, which is not so much of a cumulative issue, is DNA damage which can be cumulative with resulting disease processes. Even cell phones look to be off the hook (pun intended), but the research is on-going. The good news is that that also is frequency related and everything Bruce said still applies. Its America, people get up in arms about a transmission line a half mile away while filling there homes with cell and cordless phones, wireless networks, and anything else wireless that helps them not get off the couch.

Edited by - on

John Russell
Master Marine Consultant

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USA
3444 Posts

Response Posted - 04/28/2008 : 08:56:17

I wonder if that 1,000,000 watt radar I used to sleep next to when I was in the Air Force has anything to do with the third ear I'm growing?

It sat on the back of a 5-ton truck. At least we had a flourescent tube in its path that would glow when the thing was turned on. The idea was that if the light was glowing we weren't allowed on top of any of the "buildings" at the deployment site.

Edited by - on

ilnadi
Captain

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452 Posts

Response Posted - 04/28/2008 : 11:05:33

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by ClamBeach
 (One can appreciate that this topic is a hot potato).<hr height="1" noshade id="quote"></blockquote id="quote"> I think this Bruce wins the pun contest.

Bruce Voyager is right in the math but water heating is a power issue (think that nobody makes a 5W microwave). Molecular-level damage is an energy (i.e. short wavelength/high frequency) issue. I am not going to make any assertions as to the energy content of VHF but point y'all to the [url="http://www.fcc.gov/oet/rfsafety/"]people who are watching over us[/url].

Monty, sounds like your friend is familiar with seriously-high-power installations (megawatt; like radar & TV towers) where you worry about leakage from the transport (cables from the PAs to the antennas) and I guess people are warned to stay away from the cables just in case. In your case, the whether the connector leaks is immaterial as it is connected to bit that is supposed to leak alot (technically radiate, i.e. the antenna). In fact if the connector leaks you'll probably get less overall radiation.

As much a pain it is to run coax to your masthead (and the associated cable losses probably mean you need to run your VHF on high power) you gain a HUGE distance advantage (there are good articles around on antenna height, you can google one)

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 04/28/2008 : 20:52:17

I agree, Bruce wins.

Edited by - on

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