Ed,
You make a good point. I do however need to bring up that bandwidth needs
to be specified with a certain roll off in DB. For example a mechanical filter
in a receiver is often specified at -6, and -60 db and with a certain shape
factor.
A clean AM ham rig may be 30 Khz wide at the - 60 db points +/- 15 Khz away
from the carrier. That same rig may be 6 Khz wide at the -6 db points, and 8
Khz wide at the -20 db points. So what bandwidth is this rig?
I contend that a clean well modulated AM rig that has low distortion in the
audio, and RF modulated stage (and any linear amplifiers) will generally not
cause a problem in the ham bands when running the audio unrestricted. That is
because the voice spectrum of the average ham's voice is such that the energy
content is way down by 3-4 Khz anyway. A little roll off kicking in at 3 khz of
about 6 db / octive or more is a good thing so long as the lowpass rolloff is
preceeded with a high pass as Don has done. This needs to be taylored to the
rig, microphone, and your voice.
Look at the scenerio where the AM rig has a steep low pass filter after a
speech clipper, but the high level modulated stage has high distortion, and the
RF plate modulated stage is not linear. This rig will be wider in bandwidth
than the clean AM rig with wide open audio.
So you might say that my rigs are 30 Khz wide. Maybe so, but using the same
criteria of not specifying a roll off in DB away from the carrier level, so is
most any ham rig on the market today.
Jim
Edward B Richards <[EMAIL PROTECTED]> wrote:
What about bandwidth? +/- 5kc would be a 10 kc band width. I thought we
were supposed to limit our band width to 6kc. Please correct me if I am
wrong.
73, Ed Richards K6UUZ
On Fri, 24 Sep 2004 23:37:25 -0500 "Crawfish"
writes:
> The phone company is responsible for that illogical 3 kHz upper
> limit. The
> consonant sounds are missing unless you go above 4.4 kHz( 5 kHz is a
> good
> compromise).
>
> Joe W4AAB
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