[AMRadio] Frequency Response

Jim Candela jcandela at prodigy.net
Sat Sep 25 13:29:14 EDT 2004

    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.

Edward B Richards <zuu6k at juno.com> 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

73, Ed Richards K6UUZ

On Fri, 24 Sep 2004 23:37:25 -0500 "Crawfish" 
> 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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