Impulse noise gets stretched out in time when passed through a narrow
filter, so it must be removed ahead of the narrow filter. This is true
whether in hardware or software. Since this is a very common type of
man-made noise, effectively removing or reducing it would be very
useful. I can't see how this could possibly be done in the audio
range. It could, perhaps, at baseband in a direct sampling receiver.
In any case, a future Elecraft radio which could effectively reduce
impulse noise when a band is full of strong signals would be very
attractive, especially to urban hams. One scheme used long ago was to
use a second receiver, tuned a bit out of the band to a relatively clear
segment, to control a noise blanker in the main receiver. Could
Elecraft possibly add a mode to use the sub-receiver in this manner?
Or, because the noise-sensing receiver doesn't have to have great
selectivity, perhaps a dedicated receiver could be offered.
73,
Scott K9MA
On 8/23/2017 19:20, Kevin der Kinderen wrote:
Maybe the additional noise in the stages between where the filter would be
in IF and where it is in AF? I know I'm thinking of multi-stage RF/IF/AF
superhets and that might be what is tripping me up when it comes to a
single conversion SDR capability. Maybe there is no difference? Or maybe
components that make up a filter in an IF stage are more effective (higher
Q) than in an audio stage?
73,
Kev K4VD
On Wed, Aug 23, 2017 at 7:58 PM, Fred Jensen <[email protected]> wrote:
Doesn't appear to say very much. Other than the BW difference [RF/IF BW
might be more than ultimate AF BW], and provided that the demodulated audio
is free of IMD and other obnoxious distortion, I don't see why NR at AF
wouldn't be essentially the same as at IF. Obvious differences in the
mechanisms to do it, and I'm sure there are dozens of nits that will be
picked over this, but if you can find the signal in the noise [or the noise
obscuring the signal] at the IF frequency, I can't see any reason why you
can't do it at AF just as well.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 8/23/2017 4:06 PM, Walter Underwood wrote:
Discussion appears to be here.
https://uk.groups.yahoo.com/neo/groups/SNR_group/info?v=1&t=
directory&ch=web&pub=groups&sec=dir&slk=363 <
https://uk.groups.yahoo.com/neo/groups/SNR_group/info?v=1&t
=directory&ch=web&pub=groups&sec=dir&slk=363>
wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)
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