[TenTec] Questions about NR i.e. Orion

[Bill Tippett]

W9OY wrote:

 >I have been playing with a SDR-1k recently.  The
filter scheme in that radio allows down to a 10hz
bandwidth.  What I have discovered is there is no
ringing in a filter this narrow generated by the
algorithm used in the SDR, even if the signal being
received has a bandwidth considerably wider than 10
hz. (up to 200hz for example).  Precise tuning of the
received signal is a requirement.

         Lee I have no doubt you are reporting
exactly what you observed, but doesn't this seem to
violate the laws of physics? (i.e. receiving a 200
Hz signal through a 10 Hz filter).  Have you ever
measured the actual BW of the "10 Hz" filter?  If
not, I suspect there may be some optimism in the
setting.  Many manufacturers including Ten-Tec
do this.  For example Orion's "100 Hz" 6 dB BW
is actually around 150 Hz.  Another issue is
the shape factor of the filter.  If a "10 Hz"
filter had an extremely wide shape factor, it
would actually pass energy much wider than the
stated 6 dB BW.  If I recall, Orion's "100 Hz"
setting has a shape factor around 3:1.  This
coupled with the actual 150 Hz measured BW
accounts for the fact that Orion never rings
even at its lowest DSP BW settings.

         If the SDR-1000 folks have discovered
some way around Nyquist, Shannon and Hartley,
I would love to know how they did it.

                                         73,  Bill  W4ZV