Typical intesities of electromagnetic spectrum found outside 1

[mielke]

Does anyone know where I can find a chart of intensity vs frequency of electromagnetic radiation that can be found outside for a typical day.

 

[VEBill]

There's no such thing as typical. For example, intensity in the visible light band is much higher at noon than midnight. The amplitudes in the radio spectrum varies widely with location.

 

[mielke]

I understand this...but is there any guidance for 'typical' range/maximum. It seems like there would be studies done on this (radiation exposure on people). Like you said there is no typical but we should have a knowledge somewhere about maximum expected intensities of light and ultraviolet rays on a sunny day, radio waves in a downtown city, etc through the hole spectrum...

 

[VEBill]

Canada's Safety Code 6 defines the maximum permitted levels across the radio spectrum (in Canada). But that has little to do with actual levels. You can Google this document.

Maximum solar incident radiation levels are well defined, but keep in mind that this would be the maximum. You should be able to find this online.

Going back to the main point, by way of example: If you tune into a very strong international broadcast signal on a certain shortwave frequency, its signal amplitude might be described as "+40 dB over S9" or more. Tune the radio dial to a nearby empty channel and you might be listening to weak background noise at "S0" or less. Each S-unit is approx 6dB, so there's basically a 100+dB range of amplitudes from one radio frequency to the next. 100 dB is ten billion to one power ratio.

 

[Higgler]

Typical RF levels are so low, it's difficult to measure even with sensitive equipment.
TV and Radio stations put out the most RF. The antennas have to be physically high for safe transmission levels to humans, in addition to better aerial coverage. They put out many tens of kilowatts power.
Everything else, even cell towers transmit relatively tiny amounts of power.

 

[DHambley]

You mentioned "typical". Just recently I was working with a spectrum analyzer and I tuned in to local FM stations for fun. "Typical" signal intensities which I saw ranged from 1 nW (-90dB) to 100 nW (-70dB) for stations which were close by.

 

[Higgler]

1-100 nanowatts is low. Considering the old standard for harm to humans was 1 milliwatt per sq. cm, which is about 70 watts RF into a human...enough to raise his temp from 98.6 to 99.6 F, or so my memory thinks was the rationale for the old limit.

 

[VEBill]

Hgldr's examples are given in nanowatts (not field strength) and would thus include an unknown "antenna factor" (the antenna' transfer ratio from field strength to voltage under stated conditions, presumably including 50 ohms input impedance).

The RF spectrum has an incredible range of amplitudes. One could look up the license conditions of AM and FM broadcast stations to see what field strengths are the goal for the coverage area. But the adjacent channels might be more than 100 dB lower in amplitude. 100 dB is ten orders of magnitude.

By way of example, the ratio of the length of a bacteria (~1µm) to the length of a Blue Whale (~30m) is only "75dB" (so to speak, excuse the horrible parallel). So how long is a "typical" lifeform?