2.8 KHz is a third wider than the 2.1 filter that came in all 100,000+
Collins S-line and a large number of KWM-2. I never noticed not copying
nice audio with them though listing to very narrow FM with simpler
transmit audio was nicer than listening to SSB.
I think 2.4 is wider than necessary. I find 1.8 uncomfortably narrow.
The concepts of spectrum and using the IF shift or bandpass tuning to
adjust what spectrum is being heard is beyond the comprehension of many
amateurs. Else they'd not move frequency 500 Hz from a QSO in progress
and consider it a new frequency.
Only a FEW DSP transmitters have the capability of changing the
bandwidth without hardware changes.
SSB does use a whole lot more spectrum than CW but uses a lot less brain
power and that's important for many hams.
The switch over point is where adding bandwidth adds nothing to the
understanding of the conversation. Not necessarily where increasing that
bandwidth adds naturalness of the perceived voice. The rules currently
only require using the minimum bandwidth for communications, they say
nothing about using a wider bandwidth to sound more natural.
Then when listening for WEAK signals at the noise level or below
reducing the receiver bandwidth reduces the noise power and so enhances
the signal to noise ratio improving weak signal communication allowing
running minimum power as required by the FCC rules. All of which reduces
QRM.
Part of the problem in the past with many receivers is that reducing the
IF bandwidth didn't necessarily reduce the QRM and noise because of
intermod, blocking, and reciprocal mixing that effectively broadened the
bandwidth.
73, Jerry, K0CQ
--
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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