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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
