LSB tone vs USB tone question...

[Hawkeye351]

Got a question for the pros that I hope doesn't sound like a stupid question:

Why do some radios with USB/LSB have big changes in the tone of receive from USB to LSB?

What would cause LSB receive and transmit tone to sound nasally (tinny) sounding, although on frequency but USB receive and transmit tone would sound normal? And visa-versa...?

I've aligned many radios with no issues, but some come out with nasally (tinny) sounding LSB or USB when compared to the other SSB mode, but they sound on frequency, just has that nasally (tinny) sound.

 

[brandon7861]

Sounds like a filter passband isn't where it needs to be. IF out of whack or maybe the crystal filter drifted off freq.

SSB comes from the balanced modulator as a DSBSC signal with the frequency set where only one sideband is in the pass band of the crystal filter, with the remaining carrier and other sideband falling outside the pass band. Where the filter rolls off on both sides is where the lows are cut off.

if the filters pass band moves one way or the other (see orange highlighter), it will cut off the lows in one sideband and increase them in the other, maybe even letting some carrier through..

If this is the issue, the solution is moving the IF just a little (and noting the new alignment frequencies on the inside cover for the next guy). A signal generator and an eye on the s-meter can tell you if the passband has moved, assuming the frequency alignment went good.

 

[bob85]

you can use your ears to fine tune frequency response then put it back on frequency,
very rarely will the alignment procedure in a service manual get the best results,

The manual assumes that the filter centre frequency is spot on & the skirt shape is symmetrical, more often than not won't be.