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
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