[AMPS] Receiver performance

[Peter Chadwick]

Tom says;

>The problem is dynamic range, and the fact the DSP is way down 
>the chain from the mixers. 

Maybe we have to define exactly what is meant by dynamic range here.

It would appear from the DSP gurus that by oversampling, we should be able
to get the 'dynamic range'. My boss just brought me some text to look at on
the subject. Because oversampling appears to work by effectively averaging
the values of the samples, I can see it working on noise. I am not sure that
I can see how it does it on IMD and non linearities of that sort.

So I think I still like the idea of a first IF between 1.4 and 10MHz, and a
first filter (or filters) that are about 2.7kHz wide for SSB and selectable
between 250 and 850Hz for CW.

Then another set of filters to allow shift/width, and then DSP at audio.

A project for retirement - I have a set of 455 filters, USB, LSB, AM, all
Collins mechanical, and 500 and 250Hz crystal, as well as a lot of 1.4MHz
USB/LSB/AM and CW filters.

But with DSP on transmit, we could, at least in theory, pre-distort the SSB
signal such that even a Class C PA would give out a clean signal on SSB.
We could certainly clean up the G2DAF amp!!!

73

Peter G3RZP




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