How many radio signals in that box of space?

[stevehertz]

Have you ever stopped to wonder how many different RF signals there may be at any point in time in an imaginary 1m square 'box' in front of you? When you consider all the VHF, AM, SW, digital TV, digital radio, etc etc, it must be thousands?!! What do you reckon? It's also surprising with all that concentration that anything works! Of course that's the principle of tuned radio, the ability to 'tune in' to a single signal amongst many. It's just fantastic and fascinating in equal proportions.

[GrimJosef]

It's fascinating indeed. I wouldn't focus too tightly on the 1m box though. Unless it's a metal box none of the signals will be confined to it (and if it is a metal box then how did they get in ?). In reality they'll all be passing through it at the speed of light.

Looking at it from a slightly different point of view, I don't know where the RF-borne 'information density' would be highest -on a rush-hour railway platform with all those mobile phone signals perhaps ? Or an airport, likewise ?

I've just noticed the sub-forum title - maybe this isn't a vintage technology issue ?

Cheers,

GJ

[stevehertz]

Originally Posted by GrimJosef

I've just noticed the sub-forum title - maybe this isn't a vintage technology issue

Well, Marconi demonstrated AM transmissions in the early part of the last century, and that same system is still being used now. That's about as vintage as you can get in radio terms?

[turretslug]

It's something that's been slightly doing my head in since I was a small boy- the thought that you could take a battery radio (for the sake of "not cheating"!) into a field (at home, or the Sahara or the Antarctic....) and tune into intelligence from all over the world just out of the surrounding air. All of it crowded into that space, but separable. It's all proven and accepted science, of course, but it still seems close to magic.

[GrimJosef]

Yes. The short answer, in some senses, to the OP's question is "All of them". Of course most will be very, very weak and very possibly swamped by the stronger ones or by noise.

Cheers,

GJ

[Graham G3ZVT]

Originally Posted by stevehertz

Have you ever stopped to wonder how many different RF signals there may be at any point in time in an imaginary 1m square 'box' in front of you? When you consider all the VHF, AM, SW, digital TV, digital radio, etc etc, it must be thousands?!! What do you reckon? It's also surprising with all that concentration that anything works! Of course that's the principle of tuned radio, the ability to 'tune in' to a single signal amongst many. It's just fantastic and fascinating in equal proportions.

Yes I do, plus all the weird particles/waves coming at us from space that the boffins keep discovering, not to mention the host of stuff yet to be discovered

[stitch1]

I’ve worked around high power LF, HF etc and often wondered what effect all the man made RF that seems to saturate the air is on us, I accept probably nothing.

I did have the idea that when I win the lottery I’ll sleep in a Faraday cage a bit like Micheal Jackson and his oxygen tent

John

[stuarth]

Weren't there were some people (in America, probably) who claimed to be able to communicate with each other directly over long distances, but that their ability was blocked when broadcast radio started?

Hard to prove in the current crowded RF environment.

Stuart

[stevehertz]

Is there any evidence to suggest that being bathed in such concentrations of RF have a harmful effect on us? Personally, if there is, then I'd think it is more a question of their transmitting power than their sheer quantity. I remember past debates and arguments even over the effects of living next to power lines, also mobile phones. It is said that DECT phones are the worst because 99% of them permanently transmit at their full output power rather than vary or moderate it wrt distance from the base unit.

[GrimJosef]

Originally Posted by stevehertz

Is there any evidence to suggest that being bathed in such concentrations of RF have a harmful effect on us? ...

Nothing that's convincingly worrying, I believe. In the quantum-mechanical world of chemistry RF photons, which are very, very weedy, really aren't able to make anything happen. If you expose people to sufficiently intense microwaves then you can damage them, but those have to be high frequency and high power.

Sunlight, however, does some very bad things indeed. If you want something to worry about then it's very much more dangerous than the RF background. Of course it does some good things too.

Then there's the background ionising radiation (e.g. cosmic rays and naturally radioactive materials in the environment). If this bothers you then worry about plasterboard and smoke alarms and living in Cornwall (but don't worry much, to be honest). It's a little known fact that a fraction of our background dose comes from radioactive materials incorporated naturally in our own bones. That can be increased significantly if we spend 8 hours every day lying close to another person, since we then pick up radiation from them too.

Cheers,

GJ

[M0FYA Andy]

To say that sunlight 'does some good things' is a splendid understatement!

Without it the earth would just be a lifeless lump of rock............

Andy

[GrimJosef]

Yes. On balance I think we should stick with sunlight . We just need to remember to smear 'factor plenty' on children if they're going to be out in it a lot.

Cheers,

GJ

I wonder how the benefit of using an RF device next to your ear outside shielding it from sunlight weighs up to the affect of the RF?

[Herald1360]

It probably won't shield the top edge of your ear which is the bit that normally gets fried!

[bluepilot]

Originally Posted by stevehertz

It is said that DECT phones are the worst because 99% of them permanently transmit at their full output power rather than vary or moderate it wrt distance from the base unit.

A DECT phone only needs to work within a house or nearby so the power will presumably be much lower than a mobile phone which maybe needs to transmit over several kilometres. Also you usually won't carry it around with you, so most of the time you'll be far enough away from it that the signal strength is negligible.

[stevehertz]

I was thinking more about when it's pressed against your temple, actually in use. That's generally the area of concern, the effect on the brain, brain tumours. Here: https://www.electricsense.com/815/co...n-cell-phones/

[Hartley118]

It's quite remarkable that the advent of radio transmission in the 1920s didn't trigger all sorts of health worries about the effect of radio waves on the human body.

When we reflect on that cubic metre of space that was pretty empty of the radio part of the electromagnetic spectrum before 1920, we're fortunate that the only known effect of radio waves is to warm us up a little. Radiation of various flavours was widely believed to be beneficial, from UV through to radioactivity, so I don't expect there was any consideration given to potential damaging effects of the new fangled radio waves.

Had the invention of radio waited until 1990, one can imagine all sorts of health scares in the media!

Martin

[mark2collection]

Originally Posted by stevehertz

Have you ever stopped to wonder how many different RF signals there may be at any point in time in an imaginary 1m square 'box' in front of you? When you consider all the VHF, AM, SW, digital TV, digital radio, etc etc, it must be thousands?!! What do you reckon? It's also surprising with all that concentration that anything works! Of course that's the principle of tuned radio, the ability to 'tune in' to a single signal amongst many. It's just fantastic and fascinating in equal proportions.

So true, I've also pondered the idea of radio waves escaping to outter space, the idea of a craft which could travel fast/far enough to listen again to Churchill et al 'live' ...

I have the set, it's in fine fettle, just need the craft & some fuel, won't be back in time for tea!

A daft notion perhaps, but then ... who's to say ...

Mark

[Hartley118]

Originally Posted by mark2collection

A daft notion perhaps, but then ... who's to say ...

Einstein.

[G8HQP Dave]

The craft would have to travel faster than light. Might be easier to just invent a time machine and stay on the ground.