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

[Matt Erickson]

Some guys STILL don't get it.


At 08:30 PM 5/5/02 +1000, you wrote:
>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