[hpsdr] MDS, IMD-DR, IP3

[Bob McGwier]

Christopher T. Day wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Bob,
>
> So, if I get this right, if I'm using an SDR-1000 as the I/Q source to
> my Janus, then I should take JP3 & JP4 _out_, so that the attenuation is
> _in_ as this gives better strong signal immunity without damaging
> sensitivity as seen at the antenna input of the SDR-1000. Right?
>
>
> 	Chris - AE6VK
>
> P.S. - Anyone know if there is a Teamspeak session today? I've been out
> of touch too long. Thanks. [Berlin was very nice indeed. Museum heaven.]
>   

Yes.  With the SDR-1000,   you should leave the jumpers OFF.   You will 
be using the unbalanced plug.  The Janus improves the noise floor on my 
system over the Delta-44 by a few dB and it has much higher head room.  
The overall dynamic range improves!  The SDR-1000 is the limiting factor 
in this case.  This is a good thing.  One thing I am anxious to try once 
I get a bit further down the road,  I want to "knife" the INA's out of 
the SDR-1000,  which removes the switcher power supply influence on the 
signal path, and take the differential output from the QSD and tie 
directly to the Janus balanced inputs.  I believe this will be a great 
combination but I am going to wait a bit.  I love my Elecraft K2 but I 
don't want to lost my SDR-1000 just yet.  ;-).

I am getting very excited for HPSDR to have its first real hardware "in 
the wild".  I do hope everyone appreciates the extremely high level and 
quality of work being done on hardware and software by the participants 
in the work on Ozymandias, Janus, Atlas.

http://n4hy.smugmug.com/gallery/2061313

Bob
N4HY

>
> -----Original Message-----
> From: Robert McGwier [mailto:rwmcgwier at comcast.net] 
> Sent: Friday, October 27, 2006 11:41 AM
> To: High Performance Software Defined Radio Discussion List
> 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
>
>   


-- 
Robert W. McGwier, Ph.D.
Center for Communications Research
805 Bunn Drive
Princeton, NJ 08540
(609)-924-4600
(sig required by employer)



 1162224700.0