[AMRadio] New analog phone bandwidth petition


Larry Szendrei ne1s at securespeed.us
Sun May 15 16:47:24 EDT 2016


On 5/15/16 2:29 PM, manualman at juno.com wrote:
> The only reason I can think of to not limit the bandwidth is that it
> typically makes one sound better (for whatever that's worth).
How about these reasons:

(1) It's another -unnecessary- restriction on our freedoms which we 
should not tolerate.
(2) It's an attempt to fix something that's not broke.
(3) It's something that the FCC will not have the resources, and 
possibly not even the desire, to enforce.
(4) Some stock commercially-manufactured amateur transmitters of 
days-gone-by may not be able to meet that specification and therefore 
would become illegal. For example, I recently "swept" 3 different 
Central Electronics 20A exciters in good operating condition (and 
recently properly-aligned), and measure relative output vs. frequency 
for both the desired and undesired sideband in the SSB mode. None of 
them would meet the 8Kc @ 20dB spec EVEN IN SSB modes. This is because 
at audio frequencies above 3.5 Kc or so, the passive audio phasing 
network can't maintain it's +/- 45 degree phase relationship between the 
two audio channels which is necessary for cancellation of the undesired 
sideband, and hence those frequencies make it into the undesired 
sideband with minimal attenuation. The only way to meet this spec would 
be to severely restrict the audio bandwidth by making modifications to 
the speech amp or adding some sort of filter. (I did the latter to one 
of mine, as it's a rig I use regularly on those occasions I operate SSB, 
and I choose to occupy a channel width that's appropriate for the mode).

Probably several other good reasons exist, but that's just off the top 
of my head.

73,
-Larry/NE1S



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