[Icom] FW: A DSP IF filtering test any IC-756Pro/Pro2 owner can perform

Sun, 5 May 2002 20:30:21 +1000

g'day all on the icom reflector

this is a useful and demostrative test
i would not dispute that dsp has a role to play in a quality communications
receiver

but only as a post filter beyond a couple of good tight xtal filters which
determine the
close in two tone third order intermodulation dynamic range

the test proves conclusively that the dsp has a dynamic range in excess of
60db - big deal,
so does a typical radio shack "communications receiver" (sic), as hams we
should be getting 100dB
from the big name manufacturers rather than the 70dB to 80dB currently being
thrust upon us.
it is not all that difficult to achieve in a mass production environment

again, we should be clear in voicing this to icom, yaesu & kenwood :

(1) we are prepared to pay the extra for high dynamic range 1st mixers,
      which almost entirely determine the intermodulation dynamic range
achieved -
      if the rest of the package is of similarly high quality

(2) dsp is a useful adjunct & can entirely replace all the VBT, PBT, twin
PBT stuff
      that we grew addicted to before we understood much about
intermodulation
     dynamic range, but don't fob this stuff upon us at the expense of
dynamic range

(3) if you can't give us at least an option of tight narrow bandwidth at
first IFs in the 70MHz region
     then we can live without absolutely continuous coverage from 100kHz to
60MHz; give us a 1st IF around
     9MHz where quality discrete lattice xtal filters are cost effective (if
costly) and leave a gap in coverage
     around the first IF freq  (or in the top end rxs with sub-receivers,
let the main & sub have different
     non-overlapping coverage gaps). with cpu control & DDS as standard now,
mixing and matching
    of multiple local oscillators & IFs is a trivial exercise

just my 2 cents worth

73s gd dx de sam dellit vk4zss

----- Original Message -----
From: "Adam Farson" <[email protected]>
To: "Icom Reflector" <[email protected]>
Cc: "GEORGE T. BAKER" <[email protected]>; <[email protected]>
Sent: Sunday, May 05, 2002 3:13 PM
Subject: [Icom] FW: A DSP IF filtering test any IC-756Pro/Pro2 owner can
perform

> I am posting this test procedure to the reflector on behalf of, and by
kind
> permission of, Rob Peebles, W8LX. The test procedure can also be found on
my
> Icom page:
>
> http://www.qsl.net/ab4oj/icom/w8lx.html
>
> Best 73,
> Adam, VA7OJ/AB4OJ
> North Vancouver, BC, Canada
> http://www.qsl.net/ab4oj/
> Note new e-mail address:
> mailto:[email protected]
>