[Elecraft] Intermod or mixing?

[Joe Planisky]

Hi Larry,

I assume you've tried playing with different settings of both the IF  
and DSP noise blankers.  If not, by all means try it and use the least  
aggressive settings that make the situation tolerable.

I'm not sure how the DSP NB works, but the IF NB works by essentially  
shutting off the signal path in the IF stage for the duration of the  
noise pulse.  For relatively infrequent pulses, these brief blank  
spots in the received signal aren't very noticeable to our ears.   
However, if the blanking action is frequent (either because of the  
nature of the noise or because the threshold is set too low), the  
blanker effectively becomes a mixer combining the desired signal at  
the IF frequency with the frequency of the noise pulses (and harmonics  
thereof, etc.)  When this happens, you'll hear distortion and  
"intermod" just as you've described.  I'm afraid it's the nature of  
the beast.

Your best bet in the long run is to find and fix the source of the  
noise.  A distant second best is backing off the NB settings to find a  
compromise between the noise and the intermod that's at least tolerable.

73
--
Joe KB8AP


On Jun 12, 2010, at 2:34 PM, Larry Godek wrote:

> I've got some local noise around here that sounds like a water  
> heater or sorts or something along that line.  Anyway it's really  
> giving me fits on 6 meters.  I ahve to run the NB almost all the  
> time and that distorts the signals and sometimes it doesn't even  
> clean up the noise.  Doesn't matter if i use the preamp, attenuator,  
> Noise reduction or what.  Plus when i turn the NB on i get all sorts  
> of crap from SSb signals 40 plus kc up in the band.  If i turn the  
> NB off the SSb crud is gone.  I operate mostly in the CW portion of  
> the band.  When the NB is off i don't ahve this problem. Other than  
> finding the noise out there in the 0-90 degree quadrant anyone have  
> any idea as to whats going on?  I'm really getting sick of the SSb  
> crud showing up when the NB is on down in the CW portion of the  
> band.  I only have one antenna hooked to the radio.  What else can i  
> tell you?
>
> Larry
> W0OGH
>
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