[Elecraft] ADT-200A Fully DSP transceiver

[Paul Christensen]

> I assume the BPF shown is simply one LPF anti-aliasing filter for 
> rejecting
> signals >30 MHz.  Since the ADT was designed in Europe where 40m BCI is
> (still) a significant issue, how can the 112 dB BDR cope with the dynamic
> range of nearby broadcast stations?  Is that BPF actually a set of band
> limited filters?

Hi Bill,

Yes, the ADT-200A uses a total of nine automatically-switched half-octave 
filters in the preselector.  The specified 112 BDR figure is quoted for 2.4 
kHz BW.  As I recall, that number approaches 120 dB for typical CW BW.

I'll send you a PowerPoint presentation by private E-mail that address this 
point on page 27.  It was prepared by HB9CBU and translated by Adam Farson, 
VA7OJ.  The same presentation looks at diversity reception as an "add on" 
under development.  The four "receivers" presently come directly off one ADC 
(Lyle, there's your answer!).  So, the diversity add-on requires a companion 
ADC board for true diversity (akin to the K3's need for the 2nd Rx module).

Also, regarding adaptive predistortion, one may think ADAT is achieving 
spectacular Tx IMD numbers by under-utilizing a PA of higher power 
capability (e.g., taking a 100W PA and simply running it at half-level). 
However, the same PowerPoint presentation (page 21) shows the effect of Tx 
IMD with and without AP engaged.  Without AP, 3rd-order IMD is typical of 
+13VDC PA transceivers at roughly -33dBc.  With AP engaged, 3rd-order IMD is 
driven down to -65 dBc at 14 MHz.  In this instance, the algorithm alone 
reduced IMD by a whopping 30 dB.  Also unique to the ADT-200A is a built-in 
2-tone IMD generator for testing purposes.

I also failed to mention in past posts that the ADT-200A uses solid-state 
T/R switching like the K3 and an optically-isolated, solid-state MOSFET for 
amp switching.  The ADT unit produces no mechanical noise when transmitting 
with or without an amp.

Paul, W9AC