[Skimmertalk] CW Skimmer + RTTY Skimmer running simultaneously on Red Pitaya - Success!

[Bob Wilson, N6TV]

On Sat, Jul 1, 2017 at 8:40 AM, Tom Berry <tberry1 at triad.rr.com> wrote:

> Thanks for the good information Bob.
> Do you think the Red Pitaya is as sensitive as the QS1R?
>

Hi Tom,

Yes, if used as recommended, with the jumper moved from the factory
default, and a 14:1 transformer or similar used on the input.  I think
JF2IWL has done a lot of work comparing the skimming performance of the
QS1R and the Red Pitaya and the performance is quite similar.  Note that I
needed to use the same 10 dB pre-amp on both.

In HDSDR, with the antenna removed, I see the noise floor displayed in the
spectrum scope bouncing around at about -130 dBm at 28 MHz.  Connecting the
antenna with the 10 dB pre-amp, the noise floor rises to about -125 dBm.
That's the best measurement I can make.

I found an old thread on the Redpitaya Forum
<https://forum.redpitaya.com/viewtopic.php?f=8&t=1524> indicating that the
input impedance varies widely with frequency, and that the sensitivity is
not nearly this good, but I think that was before K1TTT discovered that you
could move a jumper
<http://wiki.k1ttt.net/Default.aspx?Page=2016%20Maintenance%20and%20Upgrade%20Blog&NS=&NoRedirect=1&AspxAutoDetectCookieSupport=1#redpitaya>
to bypass the problem and get nearly identical, if not slightly better
sensitivity, out of a QS1R.

At this point, the Red Pitaya is the only "SDR" on the market with six-band
skimming capability at a reasonable price.  I think this hardware should
have a long future, because the device is being used for so many other
purposes, instead of as just an SDR, and it is widely distributed
world-wide.  The real question is how long will the software developers be
able to keep things going, or will we be stuck on the old OS release
forever?

73,
Bob, N6TV