[hpsdr] QSD architecture and image suppression

[Bob McGwier]

Oleg:

WELCOME to hpsdr.  I have been following your personal SDR and DSP work 
for years.

As with all such engineering questions,  "it depends".  It depends on 
the care with which you work hard and layout balanced designs.  That 
said,  the image is suppressed on the decent QSD and QSE based radios better
than the traditional receivers and transmitters in almost all cases.  
BUT,  this is not really acceptable.  We must greatly exceed their 
capability because the image, especially on transmit,  falls into the 
ham band.

As you already know,  the I/Q baseband signal is a representation of a 
actual analytic signal, made from a real signal, so at one time,  it was 
in perfect quadrature before it hit the analog equipment.  This means 
there is a transformation of the signal after the roof filter/baseband  
opearation of the QSD  or before modulation/upconvert of the QSE which 
can remove this "distortion" almost completely and in fact, greatly 
exceed that of traditional designs.  This is a requirement given in band 
images.

This image rejection works well and shows that the performance is just 
excellent and you large dynamic ranges and IP3,IP2, good BDR with 
excellent A/D's, etc.

Welcome and please stay.  We can use the interaction with great people 
like you.

Is your web site with your zero-IF work still available and if so, could 
you provide a link to it for all the others to enjoy and admire your work?

Bob
N4HY



Oleg Skydan wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
>   
>
> ------------------------------------------------------------------------
>
> Hi, All!
>  
> I have seen a lot of different projects/radios based on QSD.
> I understand that most parameters can be at a competitive
> level with traditional designs, but it is still not clear for me
> how well the image suppressed?
>  
> I understand that you can get a very good image supression
> (80-100 dB is real) for the limited time with stable temperature
> and etc. But I wonder how well the image is suppressed with
> all this parameters from the real life (at least with time/temperature
> influence)?
>  
> All the best!
> Oleg
> 73 de UR3IQO
>  
> ------------------------------------------------------------------------
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