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

[Jeff Blaine]

Bob,

Specific to RTTY skimming, when looking for a processor the most 
important criteria is the floating point capability.  CPUs that have 
fine and super fact logic facilities but poor FPU will struggle in RTTY 
skimming.  The prior generation AMD chips had a pair of logic cores that 
shared a single FPU and they were particularly limited.

When I built my system for RTTY skimming last fall I picked the AMD 
2700x as a lower cost alternative to the similar Intel 6-core option and 
subsequent testing in RTTY contest loads has shown it to have enough 
horsepower for the task.  My suggestion to anyone building a system 
specifically to do multiple band RTTY skimming under contest loading 
without throttling, use the AMD 2700x as the minimum spec for a 
baseline.  The good news is AMD just released a new series of CPU and 
the 2700x should fall further.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

On 6/4/19 11:04 PM, Bob Wilson, N6TV wrote:
> 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
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