[hpsdr] Selectivity design/measurement

[Ahti Aintila]

On 16/02/07, Bill Tracey <bill at ewjt.com> wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Here's the measurements Bob McGwier and Rick Hambly did with the Janus/Ozy
> Alpha 1 boards in late October 2006 - rescued from the depths of my email
> archive.   Thanks to Bob and Rick for these.
>
> Cheers,
>
> Bill  (kd5tfd)
>
> >Date: Fri, 27 Oct 2006 14:40:41 -0400
> >From: Robert McGwier <rwmcgwier at comcast.net>
> >Subject: MDS, IMD-DR, IP3
> >
> >The Ozy, Janus perform very nicely as a receiver back end for the
> >SDR-1000.  The CPU % is low on a 1.8 GHz laptop (23%).  This all appears
> >to have been completely resolved with sufficient time on sleep to allow it
> >to enumerate again after reset.
> >
> >The attenuator being inline definitely increases the dynamic range since
> >the noise floor for the system with the SDR-1000 is NOT limited by the
> >Janus,  it is limited by the SDR-1000.  The MDS was within 0.5 dB of being
> >identical (measurement error, etc.) with or without the attenuator but
> >with the attenuator,  we can take a lot more signal before the AKM5394A
> >overloads.
> >
> >Freq,Preamp setting, MDS:
> >
> >7.0 , High, -133 dBm
> >7.0,  Med, -125 dBm
> >7.0,  Low, -120 dBm
> >7.0,  Off, -110 dBm
> >
Hi,
Just for comparison, here are my measurements with an unmodified
SDR-1000 and Waveterminal 192X card:
7.0, High, -131 dBm
7.0, Med, -123 dBm
7.0, Low, -118 dBm
7.0, Off, -108 dBm

I understand that the WT192X has internal buffer amplifiers that
actually attenuate the signal by 14 dB (or more?) before the A/D
conversion. Because of that, high gain will be needed from the
SDR-1000 resulting as overloading with the stronger signals.

I think, if used with the Janus/Ozy combination without the usual
built-in attenuators of the commercial sound cards, some hardware
modifications of the SDR-1000 will be necessary for the optimal
dynamic range. Any good suggestions???

73, Ahti OH2RZ

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