Radar emmissions and Health and Safety

[Piers]

Hi All,

Seeing there's been recent discussion on radar emissions, I thought I publish something I've been sent from Furuno re Health and Safety.

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Radar emissions is an area of concern for many people, and a question we (Furuno) receive on a fairly regular basis. Please allow me to provide you with some data on our Radars that will hopefully help clarify subject item:

The misconception lies in the fact most people look at the "Peak Power" output of the radar and think that is what is being radiated at them when they are within the beam pattern. However, that’s not the case. Radar’s radiated power has a vertical component which is directional and focused into a beam that is approximately 20 degrees wide (+/- 10 degrees from the antenna’s horizontal plane). This means that the radar’s absolute power is radiated within this sector. Energy outside of this vertical Beam width is suppressed.

Radar’s radiated power has a horizontal component that is directional and – depending on the system configuration and the specific radar antenna – ranges from 0.75 degrees to approx 6 degrees in width. RF energy outside of this horizontal Beam width is suppressed.

The energy power density of a transmitter diminishes with the square of the distance from the transmitter. This simply means that the energy levels from the transmitter drop exponentially as distance increases.

Marine Radars employ timing circuits which turn the transmitter “off” and “on” up to 2100 times a second during normal operation. During this sequence, the transmitter is only keyed for a total of approximately 1 microsecond during its transmit cycle; the remainder of the cycle the transmitter is idle (not transmitting) while the receiver is on and waiting for the transmitted energy to travel to and from surrounding targets.

Radars are rated by their Peak Power Rating. This Peak Power rating identifies the maximum radiated energy that is transmitted during the 1 microsecond interval – or one-millionth of a second – that the Radar is actually transmitting.

The Federal Communications Commission also rates Radars according to their “Average Output Power.” The Average Radiated Power of a Radar can be calculated by taking into account the fact that a Radar is only transmitting for a very short period of time during its transmit/receive cycle. We can calculate the Average Power of Radar by using the following formula:

Pavg = Ppk x pw x prt

Where:

Pavg = Average Power
Ppk = Peak Power
pw = Pulse Width
prt = Pulse Repetition Time

As an example, please consider one of our most popular Radars: The Furuno 1835 Radar. This Radar has a Peak Power rating of 4 kW (4000 Watts), it has a pulse width of .8 microseconds in long range (.0000008 Seconds), and its Pulse Repetition Time in long range is 600 Pulses per Second.

Using the formula above, we can calculate the 1831 MK-2’s average Output Power:

4000 x .0000008 x 600 = 1.92 Watts
Peak Power Pulse Width PRT Average Power Output

The average radiated Power from our 1835 (4KW) is actually less than 2 Watts!

It may be interesting to note that the RF energy levels from VHF and SSB transmitters can be 100 to 1000 times greater than the average radiated power from a 4 kW Radar. For example: Marine VHF-FM transceivers are rated at 25 Watts Output Power. When you key the mike on a VHF-FM Transceiver, the Radio transmits 25 Watts of continuous RF energy. (Approximately 1200% greater average power output than the 1835 Radar).

The environmental hazards from such a low-power system are normally insignificant. We do not, of course, recommend looking into radar that is mounted directly in front of you a few feet away on the same horizontal plane. We include a “radiation hazard” note in our Operator’s Manual that identifies what we consider the safe distance on most of our units when Radar is transmitting. An example we generally use 'withdraw' to a power level of 10 W/m² ; the unit of measurement is Watts Per Meter Squared (W/m²), and the specification for our popular 4KW radars (all of them) is 1.65 meters for 10 W/m²; this is normally thought of as a worst-case scenario.

All Radars sold in the United States comply with Federal safety standards concerning RF radiation hazards. Although the US has not set a safety distance standard for marine radars, we would rather be on the safe side.

Here are the suggested withdraw distances from one of our commercial 25Kw radar, using antennas of different length. (Per Furuno operator's manual for the FAR28X7 series) Please note: the larger the antenna results in the power is dispersed over a larger area and shorter withdraw distances.

Distance to 10W/m² point.

4 foot antenna 11.20 meters
6 foot antenna 8.60 meters
8 foot antenna 5.80 meters

S-band radar withdrawal distance would be approx the same as X-band.

Ideally, if you can stay out of the radar beam entirely, you are better off, but we all know this isn't possible in most applications.

Overall, you are advised to stay out of the withdraw area when a radar is transmitting.

Piers

 

[sarabande]

thanks for posting that, but it is Foruno marketing/H&S output which really doesn't explain in a logical, grammatical or clear way how radar works. There's little reference to the importance of frequency on tissue damage, for instance.

4/5 for trying
1/5 for content.

 

[Piers]

thanks for posting that, but it is Foruno marketing/H&S output which really doesn't explain in a logical, grammatical or clear way how radar works. There's little reference to the importance of frequency on tissue damage, for instance.

4/5 for trying
1/5 for content.

I actually found it really interesting. However, I have gone back and asked what type of injury/damage might be sustained if you were within the 'withdraw area'.

 

[nigelmercier]

I actually found it really interesting. However, I have gone back and asked what type of injury/damage might be sustained if you were within the 'withdraw area'.

It's a microwave oven with no door, figure it out.

 

[grumpy_o_g]

There's another good write up on that subject here (apologies for the link to another mag but it is one not available here). Panbo also did a highly scientific and conclusive study by taping a raw egg to a Garmin, a Raymarine and a Navico Broadband radome for a season and found that none of the eggs were hard-boiled at the end of the season, which is good enough for me.

 

[prv]

Panbo also did a highly scientific and conclusive study by taping a raw egg to a Garmin, a Raymarine and a Navico Broadband radome for a season and found that none of the eggs were hard-boiled at the end of the season

They must have smelled after being left in the sun for six months though!

Pete

 

[noelex]

The science behind Furunos response is not very impressive. Different wavelengths cannot be compared just on their power output otherwise our 20w cabin lights would be of concern.


The data from people exposed to radar emissions is poorly documented, but I have seen some very atypical health effects from people that have worked on high powered radar installations. How this relates to to the much lower doses is very difficult to know, but my advice is not to get close to the beam ( rember the emission is horizontally very narrow).

Which is what Furuno says anyway, but their rhetoric is more dismissive of the dangers than it should be.

 

[Beadle]

Perhaps you could stick a nice juicy steak to the radome and see how long it takes to cook.

I prefer medium rare.

 

[pvb]

The Furuno article is quite clear, the actual radiated power is tiny, and there aren't significant health issues.

Radars fitted on many motor cruisers are often very close to the heads of people on the flying bridge. If there was a significant risk, surely we'd find lots of brain-damaged mobo drivers?

Oh...

 

[lenseman]

. . . . . . surely we'd find lots of brain-damaged mobo drivers?

Do they have a brain?

 

[RobbieW]

To summarise the advice I was given in the '70s whilst an apprentice in the hangars at BA during Wx RADAR testing; "if your nuts feel warm, youre too close and been standing still too long" Probably accounts for much thats happened since

 

[William_H]

It's a microwave oven with no door, figure it out.

Nigel that is completely misleading and wrong. A microwave oven produces around 600w of CONTINUOUS rf energy. As compared to the 2w equivalent continuous of the Furuno calculations. Further the radar because it is scanning is giving you RF power only when it is pointed towards you. However we could consider that the RF energy of the radar is focussed by a high gain antenna so is going to give you more energy.(perhaps by a factor of around 10)
The facts are that it is fairly easy to avoid being in front of a transmitting radar antenna. Warnings etc are an easy way to avoid criticism but are probably way out of proportion to actual danger. olewill

 

[penfold]

The facts are that it is fairly easy to avoid being in front of a transmitting radar antenna.

This plus the attenuation caused by putting fleshy bits in front of the scanner mean it's not really a difficult choice; keep out the way!

 

[hlb]

I always got a head ache when on the fly with the radar on.

 

[penfold]

I always got a head ache when on the fly with the radar on.

Are you quite tall and is it a repetitive thumping pain to one side of the head?

 

[Piers]

I actually found it really interesting. However, I have gone back and asked what type of injury/damage might be sustained if you were within the 'withdraw area'.

I've had the following response to the question.

"The closer you are; the more chance of receiving negative effects. The blood in the body can dissipate heat generated by RF, to a point. Your eyes are the biggest concern because blood moves through them slower than the rest of your body. Keep in mind our suggested withdraw distances are conservative, but for your protection. It is best to be below the radar beam, that way you can be near the scanner without any problems. If you can't be out of the beam, you want to stay out of the withdraw area when transmitting."

Question: Does anyone know if their radar manual states a 'withdraw area', safe operating limit or similar? It seems to me that many radar scanners are mounted close to where crew may be, and often directly in the main beam.

 

[nigelmercier]

Nigel that is completely misleading and wrong...

OK, I was exaggerating for effect. But using your figures, would you be happy standing all day in front of a microwave oven that leaked 2W?

 

[david_bagshaw]

so the question has to be

what is the effect of using a handheld VHF on transmit, where the radiated power is right next to the head, similarly a mobile phone?

 

[penfold]

so the question has to be

what is the effect of using a handheld VHF on transmit, where the radiated power is right next to the head, similarly a mobile phone?

A handheld VHF can transmit 5W, mobiles transmit in the mW range. I use both sparingly.

 

[john_morris_uk]

A handheld VHF can transmit 5W, mobiles transmit in the mW range. I use both sparingly.

Carry on using both sparingly if it makes you happy, but with respect VHF at 5 watts and mobile phones in mW are not going to do you any harm at all. They are in the wrong part of the of the radio spectrum.

Radiation at microwave frequencies (ie Microwave oven, Radar etc) at high power are MUCH more likely to give problems. Hence the advisory note to avoid even low doses of microwave energy.

We live most of our lives in radiation from lower frequencies - you just can't avoid it.

Microwave frequencies you CAN avoid - and should for all the well documented reasons. The microwave frequencies reacts with cells and fats and water and has effects that the VHF, UHF (and even up to mobile phone frequencies of one point something Ghz) just doesn't have.

Lots of research to back this up.