The electromagnetic spectrum - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Argus25 · 20th Feb 2019, 2:09 pm

It is probably a good thing that our visual perception is limited to a restricted bandwidth, and audio perception too. There is easily far to much data to process (and ignore) in that range.

If we could hear from 1/2 a Hz to 50kHz and see across the entire EM spectrum well above and below light, we would be unable to function.

Even with the limited bandwidth of our senses it can still be problematic to try to apply our attention to the problem we are interested in and ignore extraneous data.

Notice how if you watch black & white TV for a while, you forget it is not color. We are presented already with a lot of data that is superfluous to conveying the important information.

SteveCG · 20th Feb 2019, 3:31 pm

I think it would be fair to say that the investigation of our Universe at wavelengths different from the optical did not go at a pace because the Astronomers of the pre-war era assumed that it would look fairly similar to what they were seeing on the optical - except at drastically lower resolution. Really it was the war-time experience of Solar Radio Bursts causing serious interference to the newly developed Radar systems that signalled that all was not quite what had been expected.

In the case that kalee20 mentions radio eyes would see, at those wavelengths, just 'thermal blackbody radiation' from the lamp. And it is thermal blackbody radiation that the pre-war astronomers expected to be detected at radio wavelengths. Whilst the radio radiation I've mentioned in regard to astronomical sources is being created by the complex interactions of high velocity electrons and magnetic fields.

kalee20 · 20th Feb 2019, 5:24 pm

Quote:

Originally Posted by kalee20

Quote:

Originally Posted by SteveCG

If our eyes were sensitive to radio waves instead of light waves then the sky would seem very different.

But it set me thinking, what would an electric "light" be like? Probably the business end could be a coil of wire, with AC going through it. Not a lot different to now, really!

Probably I expected readers to follow my twisted thoughts - a coil maybe 1" in diameter, energised by 100kHz AC! As opposed to a coiled tungsten filament in a vacuum, energised by 50Hz AC.

Quote:

Originally Posted by SteveCG

In the case that kalee20 mentions radio eyes would see, at those wavelengths, just 'thermal blackbody radiation' from the lamp.

No, because from the AC-energised coil, there would be a small amount of energy radiated. It could be intensified by a ferrite slug - basically a ferrite rod aerial used for transmitting.

But I did think it curious that a similar basic structure, could be used for generating energy at such hugely different frequencies!

G6Tanuki · 20th Feb 2019, 7:51 pm

Quote:

Originally Posted by Argus25

It is probably a good thing that our visual perception is limited to a restricted bandwidth, and audio perception too. There is easily far to much data to process (and ignore) in that range.

If we could hear from 1/2 a Hz to 50kHz and see across the entire EM spectrum well above and below light, we would be unable to function.

Indeed: but there are various of our coexisting furry friends [dogs, bats] whose hearing goes well-towards 100KHz, Serpents with infra-red-sensing ability, and Bees/insects who see in ultra-violet as well as the visible spectrum.

Add in various marine creatures [Electric Eels, octopi] who can detect DC/sub-1Hz electrical signals, and Whales/Dolphins who can detect similarly-low-frequency acoustics, and you have to admit that us humans live in a world of very narrow sensory-bandwidth.

Radio Wrangler · 20th Feb 2019, 10:48 pm

Quote:

Originally Posted by G6Tanuki

and you have to admit that us humans live in a world of very narrow sensory-bandwidth.

But we, unlike the others have the ability to make machines to extend our perception far beyond the abilities of any other creature. We've managed to deduce, discover and use things far beyond our direct perception.

We haven't done so bad, but did we have to use it to broadcast game-shows, the Bay City Rollers, party political broadcasts, Dynasty....

David

Argus25 · 20th Feb 2019, 11:34 pm

Quote:

Originally Posted by G6Tanuki

Add in various marine creatures [Electric Eels, octopi] who can detect DC/sub-1Hz electrical signals, and Whales/Dolphins who can detect similarly-low-frequency acoustics, and you have to admit that us humans live in a world of very narrow sensory-bandwidth.

Apparently if you roll an electrical eel up in aluminium foil, it shorts out and after half an hour it is ready to eat

20th Feb 2019, 2:09 pm	#41
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: The electromagnetic spectrum It is probably a good thing that our visual perception is limited to a restricted bandwidth, and audio perception too. There is easily far to much data to process (and ignore) in that range. If we could hear from 1/2 a Hz to 50kHz and see across the entire EM spectrum well above and below light, we would be unable to function. Even with the limited bandwidth of our senses it can still be problematic to try to apply our attention to the problem we are interested in and ignore extraneous data. Notice how if you watch black & white TV for a while, you forget it is not color. We are presented already with a lot of data that is superfluous to conveying the important information.

20th Feb 2019, 3:31 pm	#42
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: The electromagnetic spectrum I think it would be fair to say that the investigation of our Universe at wavelengths different from the optical did not go at a pace because the Astronomers of the pre-war era assumed that it would look fairly similar to what they were seeing on the optical - except at drastically lower resolution. Really it was the war-time experience of Solar Radio Bursts causing serious interference to the newly developed Radar systems that signalled that all was not quite what had been expected. In the case that kalee20 mentions radio eyes would see, at those wavelengths, just 'thermal blackbody radiation' from the lamp. And it is thermal blackbody radiation that the pre-war astronomers expected to be detected at radio wavelengths. Whilst the radio radiation I've mentioned in regard to astronomical sources is being created by the complex interactions of high velocity electrons and magnetic fields.