Safety - HF radio and children

My Sat phone has a warning about standing within 1 metre the aerial but the curly cord on the hand piece is less then a metre long :))

Mike, the Australian Radiation Protection Standards are published here http://www.arpansa.gov.au/pubs/rps/rps3.pdf
There is an overview here
http://www.arpansa.gov.au/pubs/eme/fact4.pdf
Using Table 7 (page 12) in the standard the limit for occupational
exposure averaged over any 6 minute is 1000/f-sqrd.

So if I assume a 10 metre long antenna, then at 1 metre distance the
area is 10 x 3.14 x 1 x 1 = 31 sq. m.

If 100w voice is averaged to 30 watts and there is 50% transmit and
50% receive then the average power will be 15 watts and so the
average power flux density will be 15/31 or 0.5 watts / sq m.

The safe limits are
2 MHz - 250 w/sq m
5 MHz - 40 w/sq m
7 MHz - 20 w/sq m
10 MHz - 10 w/sq m

Hope this helps.

Does that mean that 5w handheld UHF's are potentially unsafe in terms of RF energy that they output from the antenna which is usually only a few cms from your head??

G'day Mike,

this was my field for a few years in the nineties. We worked to Australian Standards AS2772.1/2 (1988) and AS 1188 (1990) it is a controversial area indeed, especially at the time as mobile phone technology was beginning to ramp up. i was responsible for carrying out surveys on all sizes of radio and tv transmitters. HF was not involved but it was one of the more complicated and dangerous frequencies we were aware of. we were always required to exercise extreme care.

RF radiation is non ionizing, i.e. it will not break molecular bonds in the body. However, it can heat it up the body tissue and can also give you nasty burns if you come into direct contact with radiating equipment, which could be induced or transmitting. As well as working on the ground and in transmitter buildings, I was required to climb towers and masts to measure two different exposure boundaries - Occupational (8 hrs) and Non-Occupational (24hrs)

Our equipment, of course, had to be strictly maintained, regularly calibrated by the Australian Radiation Authority, and checked before every operation.

I do not know if HF products such as Codan and Barrett and their associated equipment, are sold with warning, I assume they should be, but that does not mean they have warnings on those areas one may be exposed to. eg. leaning against a roo bar while the HF antenna next to you is being used for transmission by someone in the car. Indeed, pacemakers are a concern that RF users should be aware of.

kind regards,

Jeremy.

Interesting topic, however I suspect I should be more concerned about all the Radio/TV/Mobile antennas popping up around our cities than the occasional use from the HF.

Is there any detail on the exposure from a time perspective?

It must be a worry on yachts then, usually the backstay is the HF aerial which can be only 3 or 4 feet from the helmsman, in fact on some yachts, you can steer & lean against the backstay!

Well if that is the case, I should have been dead years ago; fried beyond recognition.

In these days of legal liability, I assume that any Government safety guidelines will have a good safety margin.

Here are some tables taken from the Australian Communications Management Agency website.
http://www.acma.gov.au/webwr/stds_compliance/electromagnetic_radiation/licensee_book/amateur%20radio.pdf
HUMAN EXPOSURE TO EMR: ASSESSMENT OF AMATEUR RADIO STATIONS FOR COMPLIANCE WITH ACA REQUIREMENTS

100 watt voice transmissions on SSB have an average power of 20 watts (see page 3 of 18)

TABLE 2a HF Bands (page 6 of 18)
Estimated distances (in metres) from transmitting antennas necessary to
meet [ACA-EMR] power density limits for general public exposure.
Frequency - Power=25watts
2 MHz - - - - 0.3 metres
4 MHz - - - - 0.5 metres
7 MHz - - - - 0.8 metres
14MHz - - - - 1.0 metres

TABLE 4. Omnidirectional HF quarter-wave vertical or ground plane antenna (estimated gain 1 dBi) (page 8 of 18)
Frequency - Power=25watts
4 MHz - - - - 0.5 metres
7 MHz - - - - 0.9 metres
14MHz - - - - 1.1 metres

TABLE 5. Horizontal half-wave dipole wire antenna (estimated gain 2 dBi) (page 8 of 18)
Frequency - Power=25watts
4 MHz - - - - 0.6 metres
7 MHz - - - - 1.0 metres
14MHz - - - - 1.3 metres

So I will continue to feel safe having any part of my body at least a metre away from an HF antenna while I am transmitting on VKS737 frequencies.

At 450 MHz and 10 watts continuous transmission and a 6dB gain antenna, the safe distance is 1.2 metres.

At 50 watts (some Amateur Transceivers) and 9 dB gain antenna the safe distance is 3.7m. Don't mount the antenna on the mudguard or bullbar ! The roof is the only safe place !

Hi Mike

Very aware of radiation issues and observed the damage, however I don't put the normal 4wd HF installation down as a serious risk.

While all radiation exposure should be minimized I class it as less harmfull than a mobile phone held against the ear.

The radiation risk is related to how likely it is to be able to be concentrated into a field such that a voltage gradient can be established across something as opposed to an absolute level, and this in turn is frequency related.

Its hard to focuss HF power , or to "resonate it into part of the body" compared to UHF and beyond.

Robin Miller