[hpsdr] Selectivity design/measurement

[pvharman at arach.net.au]

These measurements seem to indicate that the Janus board has a NF of ~12dB 
(with the input attenuator bypassed).

In which case it would be interesting to connect the SDR1000 QSD capacitors 
directly to the balanced inputs of Janus and run without any post QSD gain. 
This should give a useful increase in dynamic range.

73's Phil...VK6APH 
 





Quoting Bill Tracey <bill at ewjt.com>:

> ***** 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
> >
> >14.2,  High, -137 dBm
> >14.2, Med, -126 dBm
> >14.2, Low, -118 dBm
> >14.2, Off, -116 dBm
> >
> >At 14.2,  with input tones at -16 dBm and spacings at 2 kHz,  the third 
> >order product was 85.5 dBc down.  This means the IP3 is
> >-16 dBm + 85.5/2  = 26.75 dBm
> >
> >We are proceeding to use the fancy audio generator to repeat the Janus 
> >only sensitivity tests.  But again,  the extra sensitivity without the 
> >attenuator IS NOT USABLE WITH THE STOCK SDR-1000.
> >
> >More in a bit.
> >
> >Bob
> >
> >--
> >AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
> >TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
> >"You see, wire telegraph is a kind of a very, very long cat.
> >You pull his tail in New York and his head is meowing in Los
> >Angeles. Do you understand this? And radio operates exactly
> >the same way: you send signals here, they receive them there.
> >The only difference is that there is no cat." - Einstein
> 
> And the fancy audio generator results:
> 
> >Date: Fri, 27 Oct 2006 14:57:23 -0400
> >From: Robert McGwier <rwmcgwier at comcast.net>
> >
> >With a nice audio generator making 11 kHz at -20 dBm and the PowerSDR 
> >calibrated to -20 dBm,  we then removed the signal generator and 
> >terminated both inputs with 600 Ohms resistors.
> >The MDS was -135 dBm in 500 Hz with the attenuators jumpered.
> >
> >Bob
> >
> >--
> >AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
> >TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
> >"You see, wire telegraph is a kind of a very, very long cat.
> >You pull his tail in New York and his head is meowing in Los
> >Angeles. Do you understand this? And radio operates exactly
> >the same way: you send signals here, they receive them there.
> >The only difference is that there is no cat." - Einstein
> 
> 
> 
> At 04:56 PM 2/15/2007, Robert McGwier wrote:
> >***** High Performance Software Defined Radio Discussion List *****
> >
> >I did all of these measurements on the alpha Janus and Ozy boards.  The
> >AKM5394A is  one of the the  best recommendations I have ever given to
> >any project or collection of projects and the Phil's and Bill and Lyle
> >have a done a great job.   The Janus board lowers the noise floor of my
> >SDR-1000 and that system is not SDR-1000 noise limited rather than Delta
> >44 noise limited and the "hump" is gone on my set up where I used to
> >have a hump with my Delta 44.  I never had one with the Lynx L22 and it
> >uses the AKM5394A with balanced inputs.
> >
> >I am in Boston all week at Mercury computing for Cell processor
> >training  and will be at Virginia Tech next week at the wireless group
> >but I invite any of the other developers to feel free to publish the
> >numbers Hambly and I measured in the lab using the SDR-1000 and with
> >with the fancy audio generators.
> >
> >Bob
> >N4HY
> 
> .....
> 
> 
> 
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