Topband: Analog to Digital converter for 1.8MHz

[Steve Ireland]

At 01:45 PM 2/07/2004 -0400, you wrote:
>> However, the dynamic range of 71.5 dB may not do
>> so well in a contest with lots of strong signals.
>
>Steve lives where even 60dB DR may be enough.
>
>Here at my QTH, 85 dB of DR close-spaced is required, a bit
>more wide spaced. I can clearly hear the poor close spaced
>IM3DR of stock unmodified FT1000D's and rigs like the IC
>7800. I have to listen through the entire East Coast to work
>Europe.
>
>I'm sure the target value would be different in different
>areas of the world and even different areas of the United
>States, but domestically (and I suspect in Europe and Japan)
>80-90dB close spaced and 90-95dB wide spaced would be enough
>for almost any location.


VK6VZ replied:

Tom makes a good point - as he points out, the IM3DR of the stock radios
most of us use is hardly better than 70dB or so - see his web site receiver
section for details.  As he also says, where we live is the crucial point
with how much IM3DR is needed. In VK6, the nearest place of any reasonable
activity level on 160m is Japan - a lot of thousands of kilometres away...


Good luck doing that with a DSP
>system instead of a crystal or mechanical filter!

I guess the only thing to do is to try it and see how it works.  I have a
good dsp/AF back-end system to put after the A to D converter and $7 a pop
isn't too bad.  However, a single conversion superhet with a 500Hz roofing
filter after the 1st mixer, followed by the dsp back end, is probably still
a safer way to go. 

Vy 73

Steve, VK6VZ