[hpsdr] MDS, IMD-DR, IP3

[Christopher T. Day]

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.]


-----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

-- 
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