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Old 05-26-2017, 01:53 AM #17
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Default Re: Global Cyberattack Hits 150 Countries, Europol Chief Says

Quote:
Originally Posted by trencheel303 View Post
On a slight tangent here in the UK we still have BBC Radio 4 that comes to us over the "Long Wave" AM Airwaves, as well as the more usual FM and DAB, internet etc.

...

Now that is an example of still using ancient tech, as thermionic valves went out, what, in the 50s/60s?
Well no, not really.

It has everything to do with how radio waves propagate depending on frequency, not really on modulation method.

Signals used for broadcast FM (88-108 Mhz) and for DAB (220 MHz or so) do not reflect off the ionosophere under usual conditions, and are limited basically to line of sight applications. This means you need to construct a transmitter tower that is over the horizon to get coverage, which could be problematic.

To give a brief example: in the netherlands the tallest transmission tower is the gerbrandy tower which is a bit over 300 meters tall, slightly taller than the eiffel tower in paris. The horizon from that tower is about 75 kilometers, covering much of (the very flat) netherlands.

We have additional towers that provide line of sight coverage in the entire country to transmit FM and/or DAB.

But what if your country was very large, like australia, and you still want coverage most of the time? Using AM radio is still the best solution, though it will not work 24/7. Digital modes on low frequencies are certainly available like DRM (not the rights management thing!) but slowly implemented.

As in global radio, sending signals across continents, low frequency AM is still the most viable option: the receiving equipment is already there and the propagation pathways are too. Downside is low audio quality, but if you need to just get a message across it still is the most reliable method to reach any part of the world that does not have internet access somehow.


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Old 05-26-2017, 03:23 PM #18
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Default Re: Global Cyberattack Hits 150 Countries, Europol Chief Says

Quote:
Originally Posted by Benm View Post
As in global radio, sending signals across continents, low frequency AM is still the most viable option: the receiving equipment is already there and the propagation pathways are too. Downside is low audio quality, but if you need to just get a message across it still is the most reliable method to reach any part of the world that does not have internet access somehow.

If you want to get really pedantic, CW is way more reliable than AM for long distance simplex communications given the same carrier power, antenna system and propagation.
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Last edited by diachi; 05-26-2017 at 03:29 PM.
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Old 05-27-2017, 01:39 AM #19
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Default Re: Global Cyberattack Hits 150 Countries, Europol Chief Says

Well yeah, that is true, but it has some limitations:

To properly receive CW/morse code you would need to have a single sideband receiver, which are not that common and at least more complex to build compared to an AM receiver.

Also the listener must be able to understand morse code which is not very common among the general public, though many radio amateurs would.

And it is a bandwidth tradeoff as well, since you cannot really send legible morse code as fast as you can human speach.

That said, if you revert to digital modes, morse code really is not that good as it lacks any proper forward error correction. For an unreliable channel you'd probably opt for solutions lke reed-muller or golay schemes as used with singals send from deep space.

Downside to all of those is that you must know the encoding scheme and have equipment to decode it, whereas AM radio requires very little in prior knowledge or equipment.
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