[Elecraft] Noise Reduction

[K9MA]

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 <k6dgw at foothill.net> 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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-- 
Scott  K9MA

k9ma at sdellington.us