I have been using Martin's settings on my 7300 for over a year. (I arrived at these settings experimentally, collecting data on the number of decodes per sequence in the presence of strong signals.)
AGC FAST and audio level adjusted for about 55 dB on band noise, produced the largest number of decodes per sequence, but AGC off and riding the RF Gain was slightly more effective...but rarely worth the bother. BTW, Uwe's latest code, 240806, has lowered the threshold for decoding (in practice) to -15 SNR for solid decodes and -16 for occasional decodes. Prior versions were -14 for solid and -15 for rare decodes. Using FAST on N5J today on 40m, 17m and 12m showed no evidence of what Mike reported on his 7300. I did not notice any symptoms like Mike reported on either my IC-7300 (FAST AGC), or the RSPdx SDR with AGC OFF. Both receivers reported the same number of decodes per sequence and 'roughly' the same SNRs. This was done with a simple wire antenna: 80m OCF, at 42' and an auto-tuner, with deep long term QSB. JARVIS and Palmyra DXp ------ 2024-08-07 - 22:01:30 UTC - 12m - FT8 220130 -11 0.2 752 ~ JI6IHG N5J -04 220130 -11 0.2 752 ~ K1DG N5J -16 220130 -11 0.2 752 ~ W0CCR N5J -13 220130 -11 0.2 752 ~ N0AN N5J -13 N5J verified ------ 2024-08-07 - 22:02:00 UTC - 12m - FT8 220200 -12 0.2 752 ~ JI6IHG N5J RR73 220200 -12 0.2 752 ~ N0AN N5J RR73 220200 -12 0.2 752 ~ W0CCR N5J RR73 220200 -12 0.2 752 ~ HC1BI N5J -06 220200 -12 0.2 752 ~ VE4VT N5J -05 220200 -12 0.2 752 ~ JA4RQO N5J -09 220200 -12 0.2 752 ~ NR0T N5J -05 N5J verified Just Now: AGC OFF, 56 dB Band Noise (thermometer) ------ 2024-08-07 - 22:41:00 UTC - 12m - FT8 224100 -15 0.2 751 ~ JA7KHQ N5J RR73 224100 -15 0.2 751 ~ JR6LDE N5J RR73 224100 -15 0.2 751 ~ JL1CNY N5J RR73 224100 -15 0.2 751 ~ JE6RLB N5J +10 224100 -15 0.2 751 ~ JA0DBQ N5J +10 224100 -15 0.2 751 ~ JM1LSQ N5J +07 224100 -15 0.2 751 ~ N8NZM N5J -16 N5J verified 73, N0AN Hasan On Wed, Aug 7, 2024 at 3:03 PM Martin Davies G0HDB via wsjt-devel < wsjt-devel@lists.sourceforge.net> wrote: > On 7 Aug 2024 at 15:30, Black Michael via wsjt-devel wrote: > > > We noticed a phenomena on the IC-7300 where the AGC is interfering > > with SuperFox decoding. I'm interested in seeing if anybody else sees > > this on other rigs. May explain why RR73's are being missed.With AGC > > on slow we see large variations in the signal strength.With AGC off > > these variations disappear. > > > > Top one is AGC off -- bottom is AGC slow which is 3 seconds for the > IC-7300 by default. > > Operating with a rig's AGC off is fine as long as you can be ABSOLUTELY > SURE that > medium to strong incoming RF signals won't drive some part of the receiver > chain into > overload, which in turn could/will cause the generation of unwanted and > undesirable artefacts > on the audio signal that's being fed into WSJT-X. > > For example, I know by rigorous measurement that, with AGC off, the audio > output from my > present IC-7610 and also its IC-7600 predecessor begins to overload and > becomes distorted > when the RF input signal reaches a level of around -85dBm, which equates > to an S3-S4 > signal. Measurements made by Rob Sherwood NC0B on his IC-7610s have shown > almost > identical results to mine. The presence of distortion on the audio signal > going into WSJT-X is > presumably undesirable... > > On the HF bands the minimum discernible signal (MDS) of my IC-7610, as > measured by the > late Adam Farson AB4OJ and also by me, is around -126dBm with the > preamp(s) off so an > incoming signal of -85dBm is only about 40dB above that MDS level. > Assuming the audio > levels are set in accordance with the suggestion made in the WSJT-X user > documentation, > ie. to give a reading of 30dB when receiving only band noise (which could > easily be 10-15dB > higher than the rig's MDS), then it is entirely conceivable that the rig's > audio output could > become distorted when the level shown on the WSJT-X audio level > 'thermometer' is around > the 60-65dB mark, ie. well below the clipping threshold for the audio ADC > used by WSJT-X. > > The PDF document created by Rob NC0B that's available via the following > link makes for > interesting reading: > > http://nc0b.com/wsjt/ > > Based on my own findings and also those by Rob NC0B as documented in his > paper I have > for the past several years operated my IC-7610 with AGC on, with a fast > time constant set to > 0.8secs. Furthermore, I adjust the audio levels to give a WSJT-X > 'thermometer' reading of > 68dB when receiving only band noise. The rig's AGC ensures that even on > the strongest > incoming signals the reading on the 'thermometer' never exceeds about 78dB > which is below > the level at which ADC clipping is indicated by WSJT-X. Also, the > IC-7610's front-panel > 'OVF' annunciator, which indicates clipping of the rig's front-end ADC, > never illuminates > because the gain of the overall receiving chain is being controlled by the > AGC. > > Finally, I haven't yet copied N5J since they started but using the > settings I've described above > seemed to work entirely satisfactorily when I was copying and working the > K8R SuperFox. > > -- > 73, Martin G0HDB > > > -- > This email has been checked for viruses by Avast antivirus software. > www.avast.com > > > _______________________________________________ > wsjt-devel mailing list > wsjt-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/wsjt-devel >
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