[4] What differences are there between digital & analog?
Shortwave radios are sometimes distinguished from each other by their
readouts and internal tuning methods, either of which may be analog
or digital. With regard to the shortwave signals themselves: analog
is mostly used for voice transmissions; digitally, CW (Morse code),
RTTY & FSK are examples of signal modes for non-voice transmissions,
versus DRM for voice (by state-sponsored institutional supremacists).
Digital Readout: (e.g. 17.775 MHz)
There are a variety of tuning methods that provide a digital readout.
At one extreme, there are a few radios with a separate knob for each
digit. A few others have separate tuning knobs for the digits to the
left & right (the "17 & "775" above) of the decimal point (whereby
readouts are calibrated in MHz). Usually, there is a single tuning
knob to cover the entire range of available frequencies, although on
most such radios the amount of turns needed will be reduced via knobs
that have 'fast' modes, or switches that quickly select between a
variety of smaller tuning bands, or both.
At the other extreme are radios with digital readouts that have no
tuning knobs. Most of these have numeric keypads for selecting a
frequency. Some have no keypads, and so are very inflexible in use,
unless you plan to listen only to stations that you have programmed
into those radios' memories, in which case their reduced cost, size
and/or weight may better suit your needs. Many shortwave car radios
fall into the latter category, but there may be remote controls
available with keypads, if not 'rotary commanders'.
Analog Readout
There is also a wide variety of analog readouts. Some use drums or
dials that rotate under indicators. Others use cursors that run along
linear scales (sometimes as a result of pressing down on the 'presets'
found on old car radios). Selective modern radios do not use analog
readouts, but if they do, also have digital readouts, since it would
otherwise be difficult to tune to a specific shortwave frequency.
Most analog-only radios on the market are small portables that are
unselective (they cannot separate stations that are right next to
each other) and only cover the main International Broadcast bands.
Digital Tuning
This uses PLLs to electronically tune to a frequency, and allows for
stable reception of SSB signals, and storage of frequencies in memory
chips. However, the micro-electronics needed can be noisy, expensive
or power-hungry. Cheaper radios tend not to exploit further benefits,
such as scanning. On the other hand, digital radio kits that interface
with a computer exploit most of the benefits of digital tuning for
just a few hundred dollars. Digital tuning is usually accomplished by
means of keypads, and on some radios by turning knobs.
Analog Tuning
This relies on circuits which are tuned directly by you, i.e. not via
microchip control. As a result, stations tend to drift on most radios
with analog tuning, which makes SSB reception problematic. Analog
tuning is just by turning knobs (and pushing old-car-radio buttons).
However, these radios often tolerate more abuse, last longer on
batteries, and are simpler to use, than digitally-tuned radios.
_________________________________________________________________
optimised for screen reading in pine
