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Old 04 January 2012, 23:03   #31
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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.
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Old 05 January 2012, 00:27   #32
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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?
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Old 05 January 2012, 14:31   #33
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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!
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Old 05 January 2012, 15:16   #34
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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.
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Old 05 January 2012, 16:14   #35
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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.
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Old 07 January 2012, 12:37   #36
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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
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Old 07 January 2012, 18:26   #37
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Welcome to the forum Steve, at last someone who talks sense
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Old 08 January 2012, 08:29   #38
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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 thatís 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
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