[Elecraft] WSJT-X, AGC, Notch, and NB

[Bob McGraw K4TAX]

I must agree with Jim on every point.    The noise blanker does work but 
only on impulse signals.  It does little to nothing on broad band noise 
and in fact, as Jim stated,  can be degrading to the decoding of signals 
if used with broad band noise.

And I agree that reducing BW or changing  SHIFT is not an ideal means, 
but do use 2.7 kHz to 2.8 kHz for better receiver performance.  Just let 
the software do its job.   With wider bandwidths as opposed to filtering 
to lesser bandwidths, with wider BW's there is less impact on the 
decoding success of the software.   The software is designed to operate 
within the normal SSB bandwidth of the spectrum.   If there are signals 
higher in frequency or lower in frequency there is nothing wrong with 
using the "big knob" on the radio to change frequency slightly to 
receive those signals.   And again, the software knows what to do when 
it comes time to transmit.

And I find the use of slow AGC is really a must.  The electronics is 
much better than I am for determining if gain needs to be adjusted.   
Just let the superior electronics and software do the job.

73

Bob, K4TAX


On 5/13/2019 12:18 PM, Jim Brown wrote:
> On 5/13/2019 2:53 AM, Richard Lamont wrote:
>> The WSJT-X decoder has huge dynamic range (16-bit 48000 samples/sec
>> input decimated to 12000 samples/sec, so over 90 dB), so it's best to
>> use the RX as a dumb converter and let the decoder deal with it. It's
>> the right tool for the job.
>
> Yes, BUT -- while the theoretical range of a 16 bit system is 96 dB, 
> non-linearities at the lower end of the dynamic range limit it to 
> about 90 dB. That's still a lot, and it's why I recommend setting the 
> audio level as high as possible at the input of the A/D.
>
>
>> This means keeping the bandwidth of the RX at least as wide as the band
>> displayed on the waterfall and avoiding the use of anything in the K3
>> that might improve the signal for aural CW/SSB reception such as notch
>> filtering, equalisation, noise blanking and noise reduction.
>
> I will offer an alternative view on use of the NB. Yesterday, AG6EE 
> was in a rare grid in northern NV on 6M, and there was VERY strong 
> impulse noise coming from his direction. Without the NB, WSJT-X could 
> not decode him. WITH the NB, it did, and I made the QSO. I would NOT 
> recommend general use of the NB, because it generates IMD that results 
> in multiple decodes of the same signal, but there are exceptions to 
> every rule. :)
>
>> AGC should be avoided because the level of every FT8 signal in the
>> passband will be modulated by fading on the strongest signal, which
>> makes the decoder's job harder.
>
> I find that this is not a problem with AGC-S, primarily because in my 
> situation, the very strong signals are locals, not subject to QSB.
>
> 73, Jim K9YC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>