Some questions about mobile phone masts

At my workplace there was a proposal to site a mobile phone mast with two antennae on top of a sports hall. This was voted down by those in charge citing vague health concerns (people breathing heavily running around below it).

I don’t know what frequency or power it would be running, but it was proposed by Vodafone (this is in the UK) and would have been about 2 metres tall.

The sports hall roof is made of metal of some sort, I don’t know how thick, not very would be my guess. My questions are:

  1. what frequency do these things run on?

  2. what would be the typical power output?

  3. would the roof provide any sort of shielding to the people below?

  4. at the height of the antennae - 15 metres - how would the radiation exposure compare to say the typical use of a mobile handset? and to what you’d get from a wifi router?

If you want some accurate data, then this site has it:

Most sites, as I suspect you have found out, have an axe to grind and it’s hard to find unbiased scientific opinion. Part of the problem is that the ‘defence’ is usually - “There is no evidence…” It’s hard to prove a negative and there is lots of anecdotal stuff to muddy the waters.

1- A new Vodaphone tower would be 4G, and in the UK Vodaphone use 800Mhz and 2.6GHz.
2- Each 10MHz block is allocated a maximum power of 46dBm (40 Watts).Vodaphone have 2 10MHz blocks in the 800Mhz band, a 20 and a 25MHz block in the 2.6GHz band. Thus total maximum power is 260 watts. It would be unusual to actually use this power at once.
3- Yes. Precisely how much is difficult to predict, but in general you would expect significant shielding.
4- The antennae are highly directional, and they are designed to radiate power straight out and to avoid power going anywhere it doesn’t do any good (like straight down) but this is a matter of degree.

Clamping a handset to your head yields rather higher power levels on your head. About half a watt at point blank. WiFi base stations are about half the power of mobile phones. However (depending upon protocol) both can vary their power levels as needed. Even standing under a cell tower, actually using a mobile phone probably does expose you to more radiated power than comes from the tower. (Unless it is talking to that actual tower, in which both will reduce power to a minimum)

If you go stand next to such a mast for several hours straight you’ll find that your skin turns red and hurts.

So if you want to stand next to that mast for an extended period, wear sunscreen or stand in the shadow to avoid sunburn.

… or do it at night?

The worries about radiation are highly questionable (baseless, really). But when people are positing concerns about “breathing heavily” in the area, you know you are well into lala land.

Yes this is my opinion too, I’m looking for the facts so I can fight the ignorance and maybe get them to change their minds.

This got me thinking. Typical emissions are in the microwave region, right? With a maximum power output of less than 300W, this is lower than a microwave oven
(mine is rated at 800W). Microwave ovens don’t leak much and their shielding is just thin metal. Is this a reasonable analogy?

Would you find this?

iljitsch is joshing you. Sunburn.

Might the “people breathing heavily” bit not be a bit of misunderstanding, and the safety concern isn’t a “Woo! radiation!!!” one, but rather a “Big heavy metal thing fall down when the floor gets shook up by sporty types” one?

In my estimation, a microwave leaks about 2 watts. A cell phone can go as high as about 1 watt, but unlike the other stuff, that’s right next to your head.

I wouldn’t talk about shielding. Rather, look at these facts:

  1. The antennas are highly directional. They don’t send much signal down.

  2. Inverse square law. The strength of the signal diminishes with the distance squared. So if you can handle 1 watt from your cell phone at 30 cm, you can handle 250 watts from the tower at 16 times that distance = 2.5 meters.

Sort of but not really. The power levels certainly. Microwaves are difficult beasts to really tame, and they have a bit of a life of their own. A microwave oven indeed is only thin metal, and that is all you need. However ovens are carefully made and it is the precise dimensions and construction that matter. If you cut a hole in the door a pile of microwave energy can come out, and the size of the hole need not be large, just the right size. A large expanse of steel roofing would almost certainly provide shielding, but there are devils in the details. Microwaves could quite conceivably pass unhindered through a small crack that is trivially overlooked - if the crack was just the right size and shape. If you think about the wavelengths involved (2.6GHz is close to 12cm) - if this were sound it would be about 3kHz. Getting to the sort of frequencies that bounce everywhere and are hard to localise. This isn’t to say a steel roof is useless. Quite the opposite. But any sort of quantitative metric is very hard, and really impossible to predict as opposed to measure.

Microwaves are getting to the level of black magic, and engineers that design these systems will disdain lower frequencies - “anything that will go down a wire is DC”.