Understanding Radio Bands: Amplitude & Frequency

[sophiecentaur]

I think the answer is ideally yes. But the carrier would have to be on and unchanging for infinite time to have the least possible information.

People use CW (just a carrier) for communication using Morse code. The carrier is cycled on and off to form dots and dashes. The act of turning the carrier on and off spreads the frequency spectrum a little. In fact such transmitters must be constructed to turn on and off at a slow enough rate so as not to spread too far into neighboring channels.

CW is an oxymoron. The wave isn’t continuous when Morse keyed so where is the difference between that, AM and all other forms of mod?
Your post could easily Be taken to imply some hard boundary between modulation and non-modulation. Arbitrary exceptions can confuse.

 

[sophiecentaur]

In fact such transmitters must be constructed to turn on and off at a slow enough rate so as not to spread too far into neighboring channels.

Imagine you made a receiver for 'CW comms' with a very narrow band receive filter, (Bandwidth of 0.01Hz). If it were tuned spot on the carrier frequency, you would just see the carrier with no visible envelope. That's despite the fact that the carrier "isn't there" for half the time; the filter would have stored Energy at the carrier frequency for 100s or more. The modulation has been wiped off.

One great advantage of 'CW' is that you can, in fact use a receive filter with just a few Hz bandwidth which can drag the signal up from what would seem to be unusable noise levels. Of course, the Tx and Rx tuning would need to match well within a Hz or so. No problem at all these days. Great for covert comms and not requiring any fancy codulation systems.

 

[Paul Colby]

Your post could easily Be taken to imply some hard boundary between modulation and non-modulation. Arbitrary exceptions can confuse.

Agreed, but only if you don't read it and think carefully about it. CW is what people call it. It is in fact an amplitude modulation.

 

[sophiecentaur]

only if you don't read it and think carefully about it.

Ah well, that's it! Who is the intended audience for these posts? Which of us is always thinking carefully? (Present company excepted of course)

The term "CW" means two different things, according to context. If you say you picked up a CW signal, that does not imply that some old geyser was using it to send Morse with. If you say you were chatting to someone using CW, the old geyser was definitely there on his key! In my head, I was including Morse in amongst all the other mod systems. (not carefully, perhaps)

 

[Charlie Cheap]

Yes! Digital TV was marketed as ‘all-or-nothing’, either a perfect picture or none at all. But there is a slight threshold between the two. Anyone who has sat down to watch an anticipated TV programme, only to experience the blocky screen refresh and maddening cutting audio with the high-pitched ‘sssippp’ sounds, will understand why I once nearly threw my TV out of the window.

How about those times you are really into a movie and a storm moves in. I installed an old "regular" antenna just for that purpose. A flip of the switch and I am back on...if the show is locally broadcast. We lived 20+ miles out in the country and 50 miles from the towers. I stacked 2 half a wave length apart and usually got a good signal...but at that distance, not always. OH, antenna companies have been known to LIE! A 100 mile capture of TV signals...really Dude?

 

[berkeman]

The term "CW" means two different things, according to context. If you say you picked up a CW signal, that does not imply that some old geyser was using it to send Morse with. If you say you were chatting to someone using CW, the old geyser was definitely there on his key! In my head, I was including Morse in amongst all the other mod systems. (not carefully, perhaps)

https://www.yellowstonepark.com/.image/t_share/MTQ3MzIwMDY3OTc4NjM1MDU1/yellowstone_old_faithful.jpg

https://clipartstation.com/wp-content/uploads/2018/10/old-geezer-clipart-7.jpg

 

[sophiecentaur]

@berkeman
I see you found my publicity photo somewhere.
I guess the spelling is GeeZer.

 

[Paul Colby]

Dah dit dah dah dit di dah dah dit

 

[Baluncore]

Dah dit dah dah dit di dah dah dit

Some punctuation would help.
Does that begin with T, N, K or Y. Does that end with E, N, G or P.

 

[Paul Colby]

Dah dit dah dah, dit, dit dah dah dit

dit dit, dah
dit dah dah, dah dah dah, dit dit dah, dit dah dit dit, dah dit dit

 

[dlgoff]

https://www.yellowstonepark.com/.image/t_share/MTQ3MzIwMDY3OTc4NjM1MDU1/yellowstone_old_faithful.jpg
View attachment 254130

Now you've got me wondering if there's a way to modulate a geyser.

 

[sophiecentaur]

Now you've got me wondering if there's a way to modulate a geyser.

Put him in a barber’s shop quartet?

 

[Baluncore]

If you say you were chatting to someone using CW, the old geyser was definitely there on his key!

Definition of geyser. A hot spring in which water intermittently boils ...
Definition of guiser. A person in disguise, a mummer especially in a Christmas or Halloween play.

 

[sophiecentaur]

Definition of geyser. A hot spring in which water intermittently boils ...
Definition of guiser. A person in disguise, a mummer especially in a Christmas or Halloween play.

Perhaps in your part of the world, but “geezer “ and other versions is an old (usually) guy with bizarre looks, hobbies or behavior. Or sometimes a smooth operator etc.. used mainly in London.

 

[Tom.G]

Now you've got me wondering if there's a way to modulate a geyser.

Stuff a geezer in it!

 

[sophiecentaur]

Phonetic spelling "Geeezaahhh!" - to be said with feeling.