Narrowband EMI is typically from intentional transmission
sources like radio and TV stations, pagers, cell phones, and similar devices.
But is there a well-defined limit that marks the boundary between broadband and Narrowband services, can someone say that the service is internet broadband?
Since Narrowband interference affects only a small portion of the spread spectrum signal,
it can easily be removed through notch filtering without much loss of information.
PUVA is more intensive and has more side effects than broadband or Narrowband UVB,
and is usually only resorted to when treatment with the others have been unsuccessful.
(For reflective phase retarders, please see Phase Retarders.) However, most polarization altering devices-- the reflective phase retarder and waveplates--
are very wavelength sensitive and offer only Narrowband, or single wavelength operation.
The aim of pulse modulation methods is to transfer a Narrowband analog signal,
for example, a phone call over a wideband baseband channel or, in some of the schemes, as a bit stream over another digital transmission system.