[Elecraft] K3: KRX3 question

[d.cutter at ntlworld.com]

Thanks Bill, it was the first 2 that were of interest.

David
G3UNA
> > 
> 
> 
> 
> David Cutter wrote:
> > 
> > Bill
> > 
> > I can't recall seeing that figure published before; where would I look for
> > that figure?
> > 
> > David
> > G3UNA 
> >> snip
> > 
> > 
> >> The purpose of the roofing filter is mainly to reduce strong
> >> (approximately
> >> S9+30) signals from over-driving the ADC in the DSP.  If they do that,
> >> then
> >> the DSP determines the final selectivity over its ~100 dB dynamic range.
> >> 
> >> 73,  Bill
> > 
> > 
> 
> David I'm not sure which figure you meant, so I'll try to cover all bases:
> 
> 1.  S9+30 limit for over-driving ADC.  This can be deduced by the setpoint
> of the Hardware AGC Mod quoted from Elecraft's mod page below:
> 
> "This modification raises the hardware AGC threshold from about S9+5 to
> about S9+25 to +30. The new threshold still protects the DSP's
> analog-to-digital converter, while providing better receive performance when
> wider crystal filters are used."
> 
> 2.  100 dB dynamic range of DSP.  I'm not going to search for the exact
> source but this is often quoted by manufacturers as the practical limit of
> current DSPs using 24-bit ADCs.  Theoretically it should be higher based
> only on 24-bit ADC resolution but practically it's limited by other factors. 
> All hybird heterodyne/DSP rigs such as Orion, K3, FT-2000/9000 and
> IC-7700/7800 have about the same limit.  I suppose if we get 32-bit ADCs
> this limit could increase.
> 
> 3.  DSP Shape Factor formula from KK7P:
> 
> http://www.mail-archive.com/elecraft@mailman.qth.net/msg53271.html
> 
> Hopefully I covered the figure you were questioning.
> 
> 73,  Bill
> 
> 
> 

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