There is a tutorial on power and grounding for ham radio in this link.
Details of power distribution are specific to North America, but the
same principles apply inside our homes and shacks are the same worldwide.
http://k9yc.com/GroundingAndAudio.pdf
The same concepts are covered in text form in N0AX's new book on Power
and Grounding, published by ARRL. The slides in the reference above
are, in large part, the basis for that book.
73, Jim K9YC
On 7/23/2017 3:44 AM, Bill Somerville wrote:
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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