Roland,
That diagram has been wrong for a long time.? I used it at first to explain the sideband reversal when I was corrected by one of the original contributors to the BITX40 and later the uBitx.? Many people are using the original software without the modifications.? If there has been a sideband reversal, it is most likely the BFO is set above the SSB filter midpoint and reverses the sideband in the demodulator stage.
I have found that some of the documents for the BiTx series of transceivers have errors.? I try to verify with theory or inspection (of the circuit or code) to verify the information.? I had asked it to be corrected in the past.? The comments in the original v6 code agree with my prior post:
/**
?* The uBITX is an upconnversion transceiver. The first IF is at 45 MHz.
?* The first IF frequency is not exactly at 45 Mhz but about 5 khz lower,
?* this shift is due to the loading on the 45 Mhz crystal filter by the matching
?* L-network used on it's either sides.
?* The first oscillator works between 48 Mhz and 75 MHz. The signal is subtracted
?* from the first oscillator to arriive at 45 Mhz IF. Thus, it is inverted : LSB becomes USB
?* and USB becomes LSB.
?* The second IF of 11.059 Mhz has a ladder crystal filter. If a second oscillator is used at
?* 56 Mhz (appox), the signal is subtracted FROM the oscillator, inverting a second time, and arrives
?* at the 11.059 Mhz ladder filter thus doouble inversion, keeps the sidebands as they originally were.
?* If the second oscillator is at 33 Mhz, the oscilaltor is subtracated from the signal,
?* thus keeping the signal's sidebands inverted. The USB will become LSB.
?* We use this technique to switch sidebands. This is to avoid placing the lsbCarrier close to
?* 11 MHz where its fifth harmonic beats with the arduino's 16 Mhz oscillator's fourth harmonic
?*/
The one difference is the reason for the BFO frequency selection.
73
Evan
AC9TU
