[TenTec] Re: TenTec digest, Vol 1 #729 - 11 msgs

John Buck kh7t@arrl.net
Wed, 30 Oct 2002 17:44:28 -1000


OUCH!  True but nasty.  George will now have to try to recover.  Watch out.

I think an interesting alternative approach is a Tayloe quadrature mixer 
direct to the A/D and DSP.  It seems to have excellent linearity and 
dynamic range and even acts as a very narrow band front end filter.  In 
this case, the roofing filter can possibly be a digital brick wall low 
pass operating at the high side of the received bandwidth.  No other 
stages are required except the 4X VFO and divider and some gain before 
the A/D.

John KH7T

Jim, you wrote:

The argument that filters in the front end of a heterodyning
receiver are not needed if "everything" is absolutely linear
is just not so.  The mixer is not linear,  so an image reject
filter is NEEDED.  And it might as well contribute to the
narrowing of the spectrum of energy to be handled by
the entire following system as well as doing the job of image
and spurious signal product rejection.  To imply that the use
of narrow,  muti-pole crystal lattice filters following the first
mixer is a "cover up"  for poor linear design characteristics
of the front end or following stages,  is just not being technically

Lots of words,  hope this is understandable.

73,  Jim  KH7M