[TenTec] Omni VI Plus audio

[Dr. Gerald N. Johnson]

On Tue, 2008-03-18 at 18:31 -0500, Bob McGraw - K4TAX wrote:
> I suspect that you may have a defective filter.  The fact that you had to 
> pad an oscillator is a clue.  Or maybe a BFO crystal is out of tolerance.
> 
> I measured the audio frequency response of my Omni VI Plus using the 
> sinewave/power method.  Once I did this, I was able to see the shape of the 
> filter and take into account the group delay which affects the "sound" of 
> the radio. I didn't do a squarewave response however.   I also confirmed 
> that the DSP artifacts were present in the RX signal regardless of the NR or 
> Auto Notch usage.
> 
> I've found that the mechanical Collins filters used in the Omni VII offer an 
> significantly enhanced signal on SSB both in transmit and receive.  They are 
> clearly different than crystal filters regardless if they are ladder of 
> lattice configuration.
> 
> 73
> Bob K4TAX
> 
> 
Ladder filters inherently have different upper and lower skirt slopes.
They also inherently have a more rounded transition from pass band to
stop band which gives them a much better time response.

The Collins mechanical filter has enough design versatility to allow
symmetry even when neither a ladder or a lattice filter, though the S-
line vintage filters were really bad at ringing. I'm not noticing that
so much with the modern Collins CW filter in my FT-857D.

73, Jerry, K0CQ