AOR AR8000 Operating Manual page 41

AM
Amplitude Modulation - Used by broadcast services throughout the world on
medium wave and shortwave. AM is also used by VHF Civil airband, UHF
Military airband and some PMR (Private Mobile Radio) and utility services.
NFM
Narrow Band Frequency Modulation - this provides high quality communication
for relatively short distance operation. FM uses a greater frequency bandwidth
than other modes such as SSB so is less efficient.
NFM is the most common mode used above 30 MHz with the exception of the
airbands. NFM is widely used on the VHF bands: VHF Marine band, 2m
amateur Band (145MHz), 70cm amateur band (433 MHz), PMR (Private Mobile
Radio) and utilities.
In the absence of a signal, the background white noise may appear quite loud.
For ease of listening the squelch control should be rotated clockwise until the
background noise just disappears, this should be carried out when no signal is
present. The point where the background noise is cancelled is known as
"threshold point".
Do not advance the squelch control more than necessary or the receiver will
appear to be desensitised and weaker signals will be missed.
WFM
Wide band Frequency Modulation - used by VHF and UHF broadcast stations
as excellent audio quality is available due to the relatively wide frequency
bandwidth employed. Used only for local services such as VHF band-2 stereo
(received as mono on the AR8000) and UHF TV sound channels.
When listening in VERY strong signal locations especially when using an
external aerial, the WFM I.F. amplifier may be overloaded. This will not
damage the AR8000 but may result in "apparent signal loss". Should this be
encountered, use the attenuator to reduce signal strength or swap to the
standard semi-flexible whip aerial.
LSB
Lower Side Band - is a form of Single Side Band (SSB). LSB tends not to be
used commercially but is extensively used by Radio Amateurs on frequencies
below 10 MHz. This assists the separation of Commercial and Amateur users
on traditionally shared bands and prevents them from speaking to each other.
SSB is a very efficient method of transmission as the unwanted second
sideband and carrier have been removed. This allows the full transmitter
power to be employed in carrying useful information within the wanted
sideband. As a result greater distances are possible on SSB and a smaller
frequency bandwidth is required than most other modes.
The AR8000 uses true carrier re-insertion and a dedicated SSB I.F. filter so
that voice becomes intelligible. However due to the complexities of SSB,
audio never sounds 100% natural and often listeners comment on it sounding
a little like "Donald Duck" or "Micky Mouse" but this is normal and with practice
you soon become used to this characteristic.