[TenTec] Fixed BFO freq = Fixed Beat Note

[Chuck Guenther]

N6KB wrote:

"In Ten-Tec Omni VI the BFO frequency is fixed, for any given mode, using crystal oscillators. So for a narrow filter with a specific center frequency, only a specific narrow range of audio tones will be heard. Why not make the BFO variable so that we can adjust to any audio not we desire? There are a number of reasons. If the BFO were adustable, the frequency display would be incorrect (except when the BFO is just at the right frequency) or some kind of compensation would have to be made to the digital readout, or to the 1st local oscillator (VFO) frequency, without changing the displayed frequency. To accomplish this would require more control control loops of more oscillators, more complexity and likely more phase noise."
 

But doesn't the "ST" (sidetone) adjustment on the OMNI VI also adjust the BFO frequency?  

Your posting reminds me of another question that has nagged at me. Before I acquired my OMNI VI, I used a Kenwood TS-850S (which also had an adjustable sidetone/offset).  However, I don't recall having to worry about the offset frequency of the IF filters-- even the narrowest of filters (270 Hz, 250 Hz, and 125 Hz).  I'm not sure what design characteristic of the OMNI series radios requires us to purchase a first IF filter with a fixed offset frequency.  Does this have to do with the OMNI being double-conversion versus triple-conversion? 

73 de Chuck  NI0C