Subj : Re: HAM Radio
To   : Lord Gareth
From : tenser
Date : Sat Jun 06 2020 02:18 pm

On 04 Jun 2020 at 11:30p, Lord Gareth pondered and said...
 
 LG> Also, I've heard a bit about HAM radio but haven't taken the time to
 LG> dive in too deeply.  So, when you said SSB I knew it meant "Single Side
 LG> Band". However, I have absolutely no idea what that means...LOL

Radio is transmitted via radio waves.  All waves, regardless of
whether they're radio, sound, seismic, oceanic, etc, have the
same basic shape: the sine wave.  But to usually convey information,
we have the _modulate_ a wave: that is, we have to manipulate it
some way so as to encode the information we want to transmit.  On
the receiving end, we _demodulate_ it to recover the transmitted
information.

There are only a few basic ways you can manipulate a wave to
effectively modulate it for the purposes of moving information
around: you can turn it off and on (this is the basis of Morse
code, which is just a wave at a single frequency, what we call
a carrier wave, that's transmitted off-and-on in a specific
pattern that let's us encode letters, numbers, and a few
punctuation and control signals).  But you can also vary the
amplitude (basically, height) of the wave, it's frequency, and
it's phase.  There are useful information modulating "modes"
based on all of these techniques and their combinations: most
people are already familiar with AM (Amplitude Modulation) and
FM (Frequency Modulation) in which we transmit audio information
by using the base audio frequencies (which are pretty low, like,
a couple of thousand cycles per second, or a couple of kilohertz)
to modulate the much high-frequency radio carrier wave we
actually transmit: in AM, we use the audio frequencies to guide
the amplitude of the transmitted carrier; in FM, we vary the
radio carrier frequency in a way that corresponds to the audio
base-band frequencies.

When we modulate a wave to transfer information, doing so requires
a certain amount of "bandwidth", or part of the radio spectrum, to
hold the transmitted signal.  The spectrum of frequencies is large,
but not infinite; thus, we'd like to compress the amount of bandwidth
we use if possible.

An interesting property of AM is that the upper and lower halves
(or sidebands) of a wave are mirror images of each other: this
means that we really only need to transfer one sideband; we can
reconstruct the other on the receiving side.  Furthermore, if
we know the carrier frequency, we can filter that out of the
transmission too, thus saving a little bit of bandwidth.

And so that's what SSB is: the transmission of an amplitude-modulated
radio signal conveying audio base-band information by suppressing one
of the AM sidebands and possibly the carrier: this uses only half
of the bandwidth of the corresponding AM transmission, which is
much more efficient use of the available spectrum.

--- Mystic BBS v1.12 A46 2020/05/28 (Windows/32)
 * Origin: Agency BBS | Dunedin, New Zealand | agency.bbs.nz (21:1/101)

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