[hpsdr] Selectivity design/measurement

[Tayloe Dan-P26412]

> And the fancy audio generator results:
> 
> >Date: Fri, 27 Oct 2006 14:57:23 -0400
> >From: Robert McGwier <rwmcgwier at comcast.net
<http://lists.hpsdr.org/listinfo.cgi/hpsdr-hpsdr.org> >
> >
> >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
> >

If the MDS is -135 in a 500 Hz bandwidth with just a signal generator,
what was the largest signal that be injected without harmonic artifacts
showing up?  

>From the specifications of the AKM5394A, it appears as if the difference
between the differential inputs is 2.25v max. If I think of this as the
direct detector outputs (no post detector audio pre-amp at all), then
the largest input signal will be half of this or 1.12v pk, or 2.25v
pk-pk, since the A/D converter will have at is balanced input signals
with the polarity of +S and -S at the same time.  2.25 volts pk-pk makes
sense, since the A/D converter will differently sum these two
differential inputs into a new signal of 4.5v pk-pk, a reasonable limit
given the 5v supply voltage used.

Since ~ 610 mV pk-pk corresponds to a 0 dbm RF input on the detector,
2.25v pk-pk is a maximum input of +11.5 dbm before blocking.  Thus the
blocking dynamic range should be +11.5 - (-135) or 145 db of blocking
dynamic range.  That would indeed be excellent performance.  

When I designed the NC2030 (a narrow band analog DC phasing receiver)
using this type detector, I got 142 to 145 db blocking dynamic range 10
KHz away from the desired frequency.  At that point, the limiting factor
that I ran into was LO phase noise and the LO that I used was very
clean.  This implies a strong emphasis on LO phase noise in order to
take advantage of the outstanding performance of this new A/D converter
board.

No post detector amplifier needed!  145 db of potential blocking dynamic
range!  Wow! HPSDR indeed.

Great job guys!

Was there any testing on the IP3 of the new sound card?

With no post detector amplification needed, it implies that the detector
should have very, very short audio connections to the A/D converter.

- Dan, N7VE

 1171908463.0