Handheld radios

[mister p]

SPR, sorry I meant 71's not 8's

[rigi36]

I'm being serious. Is it serious enough to move it. VHF doesn't get used often.

[SPR]

Originally Posted by maxhar

I'm being serious. Is it serious enough to move it. VHF doesn't get used often.

I was too! but only device I know needs mounts at least 6 foot away is radar!

The amount of time you use your radio, I think not an issue...

s.

[chewy]

Originally Posted by maxhar

I'm being serious. Is it serious enough to move it. VHF doesn't get used often.

Google VHF health issue or harmful and see what comes up, nothing of any relevance to VHF radios.
I think how close the VHF aerial is to your head is would be the least of my worries these days....

[Erin]

Well Garmin seem to think the aerial should be mounted at least 1.5m from any persons in their instructions.

I've always been under the impression that it should be away from people when transmitting. 25watts at whatever radio frequency is quite a lot of power.

…..”All the effects appear to be worse as the frequency is raised. A serious side effect of exposure at frequencies above 150 Mhz, (that is VHF and above), is that body parts can become resonant absorbers, which raises the amount of energy taken in, and reduces the threshold exposure level at which effects are seen.”

[captnjack]

Originally Posted by maxhar

I'm being serious. Is it serious enough to move it. VHF doesn't get used often.

Then I wouldn't worry about it. If the aerial were continuous duty it would be of greater concern.

There are RF limits and a 25W aerial 1m from your head definitely exceeds what the HAM radio community would do for instance. Here is a table for the US occupational health standards.
Section

Marine VHF is in the 156-174Mhz range so the middle line on the table.

The problem is knowing the radiation pattern of your aerial. For simplicity sake I am going to call it 1/2 of a sphere. It does not transmit up or down for instance. A 1m diameter sphere has a surface area of about 12.5m or 125000 cm2. 1/2 of that is 62500 cm2.

25w maximum power = 25000 mW
25000/62500 = 0.4 mW/cm2

About 2x what you'd be allowed to exposure your neighbor to if you mounted the aerial on an apartment building. But a little less than half of a "controlled" occupational exposure. This depends significantly on the radiation pattern of your aerial.

Since your duty cycle is small I wouldn't worry about it. With any kind of RF energy, use the low power setting if you can communicate with that and only use 25W if required. There's no RF issue with receiving full time.

[Poly]

Originally Posted by captnjack

There are RF limits and a 25W aerial 1m from your head definitely exceeds what the HAM radio community would do for instance.

Have you met "ham radio guys"? I'm not sure if they start out like that or its the exposure...

[Vandad]

Originally Posted by chewy

Who told you this as it sounds like bollocks to me.
A radar is transmitting all the time it is turned on, even IF a VHF did cause a health hazard it would only do this when it is transmitting.

OK, that's because you don't know the effect of radiation on the body.

It is because the antenna converts currents which comes from the radio device into radio waves. The increased signal strength of the handheld radio antennas is achieved by concentrating the signal into various narrow discs and therefore, the signals are much more
focused. So it is received better by the receiver. At the same time the signals are moving to all directions (horizontally => line-of-sight system).

In medicine, Electromagnetic radiation and health are discussed quite widely and something called "Specific absorption rate" (Watt/kg) is used to measure it. So it measure the rate of enegry absorbed by the body or even tissue. That was a hot topic in 1990s when mobile phones first came!

Therefore, most radio manufacturers follow the guidance of US military/IEEE which has set out some limits on how much especially the handheld radios can be powered. Potentially, one reason behind not having a 25W handheld radio other than the limited bettery life could be this.

Whether it harms your brain or not, most researchers have found little evidence, but the limits have not yet been changed!

[Vandad]

Originally Posted by martini

You need a license to transmit at any power level up to 25W. Anything over 25W is illegal, whether you have a license or not.

We have 50W or 100W+ station radios. I meant the station radio license not the VHF user license.

[martini]

Originally Posted by SPR

yes - and that mobile phone you use, x-rays and microwaves are not helping much either....

not forgetting the Wi-Fi and Cordless phone waves....

hence I wear a tin foil hat!

S.

I can vouch for the power of microwaves at least, buried a good friend of mine last week after he decided to open up his oven and have tinker with it

[captnjack]

Originally Posted by Vandad

The increased signal strength of the handheld radio antennas is achieved by concentrating the signal into various narrow discs and therefore, the signals are much more
focused. So it is received better by the receiver. At the same time the signals are moving to all directions (horizontally => line-of-sight system).

Short whip antennas on handheld's transmit in a very broad pattern to compensate for the fact they may be tilt at odd angles during transmit. The only areas they don't transmit are straight out the end and towards the radio itself.

This concept has been discussed many times before, its the reason you don't really want a "high gain" antenna on a RIB nor on the end of a sailboat mast as both bobs around in the swell constantly changing radiated direction.

[chewy]

Originally Posted by Vandad

OK, that's because you don't know the effect of radiation on the body.

I understand enough to know it won't do you any good.
Even if a VHF aerial does emit harmful radiation it will only do so when transmitting, agree?

[Vandad]

Originally Posted by chewy

I understand enough to know it won't do you any good.
Even if a VHF aerial does emit harmful radiation it will only do so when transmitting, agree?

Absolutely, I am not saying it is 100% harmful, it is the job of scientists to prove it!

But as I said manufacturers must follow the standards. The standards are developed to protect against even unexpected consequences; known or unknown!

One good example is that in Aircraft Fueling depots, and in particular in the Army, the Handheld radios are limited to only 3W and the personnel are not even allowed to transmit whilst the aircraft is being refueled.

The amount of power needed to cause fire (igniting the petrol) from a radio wave is much Higher than the power which could cause health problem.

At the same time, the airplanes' radio are using much higher power compared to handheld!

[mister p]

I know a commercial pilot of both exec jets and passenger 'planes that tells me there is no policy on crew not transmitting whilst refuelling......this includes mobiles.
His somewhat interesting log additions are emails, with attachments showing refuelling taken from cockpit to failsafe the aircrafts apron time.

[chewy]

Originally Posted by Vandad

Absolutely, I am not saying it is 100% harmful, it is the job of scientists to prove it!

But as I said manufacturers must follow the standards. The standards are developed to protect against even unexpected consequences; known or unknown!

One good example is that in Aircraft Fueling depots, and in particular in the Army, the Handheld radios are limited to only 3W and the personnel are not even allowed to transmit whilst the aircraft is being refueled.

The amount of power needed to cause fire (igniting the petrol) from a radio wave is much Higher than the power which could cause health problem.

At the same time, the airplanes' radio are using much higher power compared to handheld!

If the radio has the appropriate Ex rating then they won't be an issue.

[Copinsay]

Hi there

In the wider radio world, it's not uncommon to hook up a handheld to an external antenna to increase its range. Indeed, this is commonly done on other systems where handhelds are used inside a building.

This does not increase the unit's rated power output though, it just enables the signal to be transmitted more efficiently. And as long as the separate antenna is connected correctly, there is actually less theoretical hazard to the user, as the radio signals are transmitted from the external/separate antenna, rather than from the flexible one close to the person's head.

Using a more effective antenna will increase the "effective radiated power" (as the signal gets out into the air more effectively) but this does not increase the power coming out of the handheld... It will still be 6w, 5w or whatever.

Think of an external/better antenna as being like a better lubricated bearing, or tyre with less rolling resistance on a car etc; the engine power is the same, but it is used more efficiently.

One practical drawback can be that the BNC coupling (or whatever) from the top of the handheld to the external antenna may not be as waterproof as with the flexible rubber one supplied.

Hope this helps.

Best wishes

Steve

[chewy]

Welcome to the forum Steve, at last someone who talks sense

[Copinsay]

Hi there Chewy and all.

Happy to help - I joined as I want to learn more about ribs, but as a former communications engineer, I'm happy to help others where I can, rather than just always take information!

I hope it came across as helpful, as while it's great there's just a lively community keen to contribute, I wanted to make it clear that using an external antenna properly would be technically even "safer" than the antenna by the head.

The whole issue is quite complex as the frequency, duty cycles (as someone else stated) and pulsation can all make a very big difference. When working in the NHS we use various radio waves intentionally to warm or simulate muscle and other human tissue for beneficial effect. So it all depends, and thus generalisations between a microwave oven and a VHF handheld are not always the best basis for decision-making.

But all contributions were clearly well intentioned so I think that’s a good thing... I look forward to a similarly helpful debate about my posting about the best electronic charts around Orkney and the North coast of Scotland :o)

Beats wishes and thanks for the welcome.

Steve