[Skimmertalk] Red Pitaya STEMlab SDR 122-16 now online at N6TV

[Bob Wilson, N6TV]

I've replaced two (2) Red Pitaya 125-14 boards with a single STEMlab SDR
122-16, which is now online.  It is currently set up to skim 192 kHz slices
on 3.5, 7, 10, 14, 18, 21, and 28 MHz, running CW Skimmer Server and RTTY
Skimmer Server via CWSL_Tee on the first MAC address, and 45, 384, 1800,
5330, 24890, 28200 and 50000 kHz CW only skimming on the second MAC
address.  The "top" command on Alpine Linux reports about 35% CPU
Utilization for the first MAC address (eth0), and 44% CPU for the second
virtual MAC address (mvl0 - "Mac VLAN") (total, 79%).  I removed the 14:1
impedance transformer, but kept the 10 dB Clifton Labs preamp for now,
which I may end up removing.

The critical thing I had to remember to do was to update CWSL_Tee.cfg in
the RBN directory to use the new MAC address, as well as renaming
HermesIntf_XXXX.dll to match the address I wanted each skimmer to use.

The only problem I'm seeing is very broad and loud AM or FM broadcast band
(?) inter-mod at the top and bottom ends of the two 10m segments, as shown
here:

https://www.kkn.net/~n6tv/STEMlab_SDR_122-16_Intermod_N6TV.png

The screen shots are from HDSDR via Extio_CWSL.dll and Extio_CWSL2.dll.

There are FM broadcast stations very close to me, but the closest AM
broadcast station is a few miles away.

The antenna is a VE3DO loop
<http://www.ok1rr.com/index.php/antennas/8-the-ve3do-receiving-loop> (passive
antenna) which isn't particularly sensitive on 10m, but I saw some of the
same inter-mod issues on my Pixel loop (active preamp).

Switching back to the STEMlab SDR 125-14 with the same VE3DO loop antenna
and preamp, but with the 14:1 transformer inline, I see only a little bit
of the same interference (it is much weaker).  It disappears completely
when I disconnect the antenna.

I tried bypassing the preamp, but it made little difference.  Maybe I need
a high-pass or low-pass filter on the SDR input, or both, or a broadcast
band filter.  I haven't identified the station yet.

Other than those issues, I'm pleased with the replacement, as now I can do
with a single Red Pitaya SDR what I was previously doing with two different
boards.

Now if only there was a way to start both instances of CW Skimmer Server
automatically from the Aggregator.  For now, the second has to be started
manually, same as before.  Terminating the second skimmer immediately stops
the first, so  have to restart (the "NOW" button the the Aggregator .INI
tab is very handy for this).

The CPU is an Intel i7-7700 3.6 GHz, CPU Mark 10731.  I think 7 bands of
RTTY Skimming is the maximum it can handle.  The Windows CPU utilization
runs about 65-70%, but much higher when there are lots of RTTY signals on
the bands.  Network throughput to the SDR seems to be a steady 150 Mbps
over 1 Gb Ethernet with 14 bands x 192 kHz.

This web site below is a good reference to check CPU speed for just about
any processor you might consider using for RTTY Skimming:

https://www.cpubenchmark.net/CPU_mega_page.html

Just about any processor can handle CW Skimming.

73,
Bob, N6TV