On 23/07/2017 11:33, Costantino Cerrotta wrote:
how can I stop the multiple decodes in FT8 mode??? Sometimes, when signals are strong, I receive signal with 100hz spacing. Thanks in advance
Hi Costy,spurious images of signals spaced at two times the line frequency are due to mixing with PSU hum in the audio domain, this can happen either at the transmitting station or at the receiving station. You need good quality earth returns to your power supplies and also to ensure that devices using different power supplies and connected by signal paths have their earths well bonded to each other or that the signal paths are fully air gap isolated with transformers or other optical based isolation.
One simple check to see if you have a problem is to tune to a band where there are very strong signals from an area with a different line frequency from your own. For example your line frequency is 50Hz and North America is 60Hz, so if you see images on DX signals from NA with 100Hz spacing then the problem is at your station.
Spurious images more that 40 dB below the wanted signal are probably acceptable although better is of course desirable.
73 Bill G4WJS.
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