There are two common causes of sidebands with a station that is properly
adjusted and uses good equipment.
1) The best gear (Elecraft K3, K3S, or a Flex 6000-series), and a first
class power amp) have sidebands roughly 40 dB down on both sides of
their signal due to IM distortion in the RF stages. These sidebands are
generally symmetrical, and the total -40 dB bandwidth is about 680 Hz.
2) Doppler shift produced by reflections from aircraft. These sidebands
are generally asymmetrical (that is, on one side or the other of the
main signal). Here in the SF Bay Area, which includes Silicon Valley and
extends down along the Monterey Bay, we have glide paths for major
airports in San Jose and San Francisco.
There are roughly a dozen or so locals running 500W with gear like this,
and we all regularly experience what you're seeing.
73, Jim K9YC
On 7/5/2019 11:02 PM, Paul Kube wrote:
’ve seen various kinds of problematic FT8 signals that I think I
understand -- “barcode” harmonics etc. – but what is going on here:
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