On May 14, 2007, at 5:32 AM, Don Wilhelm wrote:
John,
Thanks for that additional info - I had forgotten about the Bessel
filter.
There is a distinct advantage with the K3, the 'roofing filter' is
not the major element in setting the rolloff of the total filtering
and the ultimate receiver selectivity because that aspect is
handled by the DSP. That makes the use of roofing filters with a
slow rolloff (not steep skirts) quite feasible.
I believe we should be looking at group delay filter
characteristics more closely for use with data modes, especially
with the advent of digital voice mode.
That is especially true if you are trying to put all your bits on one
carrier. If you opt for something like OFDM (multiple carriers) and a
lower symbol rate, each carrier and its sidebands will be narrower
and will not have as much delay skew across that carrier and its
sidebands. In that case center-to-edge group delay spread is less
harmful.
OTOH, it will be critical for trying to dig a really weak narrow
signal out.
Yeah, I agree with you. I really want to see what the filters are
going to look like.
73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com
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