[hpsdr] QSD architecture and image suppression

[Ahti Aintila]

Bob,

Obviously you mean this site: http://t03dsp.skydan.in.ua//index.htm
It is working and last updated 09/19/2007. It shows Oleg's great work.

Bob, you are right about the risk of destroying the perfect balance of
the digitally generated signal by analog means in zero-IF and low-IF
frequency translators (aka mixers). All balance errors and clock
spurii end into our own ham bands. No practical filter can remove
them.  We have to take care of the best possible balance and
suppression of the spurious frequencies from the DDS or PLL circuits.

And Oleg, thank you for your web site. Welcome back and please, inform
us if there is something more and new to come.

73, Ahti OH2RZ


On 20/02/2008, Bob McGwier <rwmcgwier at gmail.com> wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> 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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