The ubitx filter are low pass design. The Ubitx has NO band pass filters.
The Bitx40 current has a filter that has a peaked low pass. The really old
versions of the bitx20 had a true band pass.
if your VFO is in the 5Mhz range you will see 9mhz IF +vfo and 9MHZ if - VFO
there is no mystery as hams have use that trick for year to get dual band
radios.
So first you bandpass filter is very poor is you can hear 80M at all!
Second Your BFO is likely not set right and 20M (nomally USB) the
product detection is suffering and since 80M is nominally LSB if it
sounds better fix the BFO.
FYI harmonics of SSB signals are unintelligible, always.
You are getting an IMAGE response due to poor input filters.
Allison
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