I was reading the ICOM manual for a new VHF installation and noted the
warning shown below.  It strikes me that very few of our boats comply with  these
requirements.  On my boat, the antennas are on top of the pilothouse  but not
far enough above my head.  On the installation this spring, there  will be 4 ft
antenna extensions.  Perhaps Bob Austin or someone else with a  medical
background or knowledge might enlighten us on the risks posed by RF  exposure that
we are likely all getting.

Icom requires the radio operator to meet the FCC Requirements for Radio
Frequency Exposure. An omnidirectional antenna with gain not greater than 9 dBi
must be mounted a minimum of 5 meters (measured from the lowest point of the
antenna) vertically above the main deck and all possible personnel. This is the
minimum safe separation distance estimated to meet all RF exposure
compliance  requirements. This 5 meter distance is based on the FCC Safe Maximum
Permissible  Exposure (MPE) distance of 3 meters added to the height of an adult (2
meters)  and is appropriate for all vessels. For watercraft without suitable
structures,  the antenna must be mounted so as to maintain a minimum of 1 meter
vertically  between the antenna, (measured from the lowest point of the
antenna), to the  heads of all persons AND all persons must stay outside of the 3
meter MPE  radius. Do not transmit with radio and antenna when persons are
within the MPE  radius of the antenna, unless such persons (such as driver or
radio operator)  are shielded from antenna field by a grounded metallic barrier.
The MPE Radius  is the minimum distance from the antenna axis that person
should maintain in  order to avoid RF exposure higher than the allowable MPE level
set by  FCC.
FAILURE TO OBSERVE THESE LIMITS MAY ALLOW THOSE WITHIN THE MPE RADIUS TO
EXPERIENCE RF RADIATION ABSORPTION WHICH EXCEEDS THE FCC MAXIMUM PERMISSIBLE
EXPOSURE (MPE) LIMIT....

It notes that the MPE is determined assuming a radius of 3M, maximum power
of the radio and a 9dBi antenna.

Jim

(Jim & Mim McCrea, mcc272@aol.com Nordic Tug 37-134  "North Star" Home Port
Norwalk, CT)

Saturday, February 19, 2005, 2:32:29 PM, McC272 wrote:

Mac> I was reading the ICOM manual for a new VHF installation and noted the
Mac> warning shown below.  It strikes me that very few of our boats comply with  these
Mac> requirements.  On my boat, the antennas are on top of the pilothouse  but not
Mac> far enough above my head.  On the installation this spring, there will be 4 ft
Mac> antenna extensions.  Perhaps Bob Austin or someone else with a  medical
Mac> background or knowledge might enlighten us on the risks posed by RF  exposure that
Mac> we are likely all getting.

RayMarine has a similar warning in their Ray54 manual, but refers to a 3dB antenna and lists smaller distances.  I expect most of us will use a 6dBi antenna, so if we want to obey the warnings, we should try for half way between the Raymarine and Icom distances.  However, I think even the RayMarine distances are impractical on my (and probably most) boats - I'd need a 10 ft mast for 3dB antenna, with the base of the mast mounted to the side of the flybridge.  With a 6 dBi antenna, I'd need a 15 ft mast, plus an 8 ft antenna - a bit much for a 20 ft power boat!

I can't speak to the health concerns, but will observe that we've all been violating these warnings for years, and the current radios are no more powerful than the ones we bought in 1980.

RayMarine's warning note:

========
This system has a Maximum Permissible Exposure (MPE) Radius of 1.5
meters (per OET Bulletin 65), assuming the maximum power of the radio
and antennas with a maximum gain of 3dBi. Accounting for the height of an
average adult (2 meters) the minimum height of the antenna above the deck
to meet RF exposure compliance requirements is 3.5 meters.
For watercraft with suitable structures, an omnidirectional antenna with gain
not greater than 3 dBi must be mounted a minimum of 3.5 meters vertically
above the main deck and all persons on board. For watercraft without suitable
structures, the antenna must be mounted so as to maintain a minimum of 1.5
meters vertically between the antenna (measured from the lowest point of the
antenna), to the heads of all persons.
Do not transmit when anyone is within the MPE radius of the antenna, unless
shielded from the antenna field by a grounded metallic barrier.

--
Peter Bennett, VE7CEI    Vancouver, B.C., Canada
Lien Hwa 28 (AKA Polaris 30) "Sea Spray"
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

Saturday, February 19, 2005, 3:38:10 PM, Peter wrote:

PB> With a 6 dBi antenna, I'd need a
PB> 15 ft mast, plus an 8 ft antenna - a bit much for a 20 ft power boat!

Arggghh!  Make that a 28 ft boat. (damn keyboard :-) )

--
Peter Bennett, VE7CEI    Vancouver, B.C., Canada
Lien Hwa 28 (AKA Polaris 30) "Sea Spray"
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

My website has a compliance calculator for those that wish to play.  You
will find it here:

http://www.wirelessconnections.net/calcs/rfsafety.asp

Mike

Mike Cowan
MV Sue's Pool III
65 Hatteras LRC hull #2
Off-List email: mikec@wirelessconnections.net

Jim McRae wrote:

On the installation this spring, there  will be 4 ft
antenna extensions.

Jim, we have the base mounts for our antennas roughly four feet above the
side decks on the sides of the wheelhouse.  We have 8-foot extensions, with
25-foot fiberglass whips, giving an effective height of about 43 feet above
the waterline to the tips.  They give significantly better range than most
of the boats in our area.  The only problem comes when running in the canal
system or under bridges - you have to check the clearances carefully.  (I
knocked the tip off one a couple of years ago on a bridge identified as
having a clearance of 45 feet) If you are planning a new installation, and
want to comply with the directions set out by ICOM, might I suggest you use
longer extensions.  5 meters is something over 16 feet, and a four-foot
extension may not comply with the FCC Requirements.  Unless of course, you
have a pilothouse that is 12 feet tall!

The advantages are improved range and increased separation from your head.
The cost differential should not be that great.

Bob Davies
Toronto

(SNIP) How many boats have you seen with the radar mounted on the flybridge
crotch high?  Harry

Too many!  But there is a bright side-- Where do you think they get the
singers for the "Vienna boy's choir"?

                                      Regards....

Phil Rosch
Old Harbor Consulting
M/V Curmudgeon MT-44TC
Currently Lying Highborne Cay, Exuma, BA.