On 17/03/2017 18:27, Gordon Higgins wrote: > Hi bill not no if this is the right place to ask this ? > > i am noticing a lot off stations on jt9 that print up more than once > on my screen they are usale +8 or more and secondary prints are > normaly -20 or more had on station print up 17 timems i run WXJT-X > v1.7.1 r7441 any comment i to have been told that i have multy > decodes @ local stations usaly @ -20 or more below my main signal no > problem on jt65 any help appritated
Hi Gordon, no problem asking here although in future it helps everyone if you start a new thread rather than post unrelated questions as replies to existing message threads. There are normally two causes of multiple decodes of station's signals. Both are related and likely to be due to some level of line hum in an audio circuit. This can happen at the transmitting station in which case the mixing products are being transmitted on air. The line noise tends to be at twice the local line frequency due to power supply rectification methods. So signals from a station on a 50Hz line frequency may have spurious mixing products at +/- 100Hz, +/- 200Hz etc. and a station on a 60Hz line frequency may have spurii at +/- 120Hz, +/-240Hz etc.. It is very hard to totally eliminate all sources of hum in audio circuits, especially when connected between equipment. If the strongest spurious mixing product is at least 40dB down on the main signal then it is reasonably OK and acceptable. The same problem can occur at the receiving station, this is less serious as the spurii are not transmitted although eliminating them can only help. If you find all strong signals suffer this issue, roughly in proportion to the main signal strength, then the receiving station is probably at fault, if only few stations exhibit this issue, especially when there are stronger ones that do not, then the transmitting station is probably at fault. Good quality earth bonding between PCs and rigs usually helps with minor cases although this can be difficult with laptop PCs. Note that these effects are different from another often seen where one or more weaker versions of a signal at higher frequencies are seen. When these are harmonic products their main characteristic is that they are wider by a multiple of the harmonic number plus 1. These will not be decoded but may be apparent on the waterfall and 2D spectrum displays. These are usually due to audio level overdrive causing clipping distortion and most commonly caused at the transmitting station. 73 Bill G4WJS. ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ wsjt-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel
