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

[Jeff Blaine]

Bob,

There's not a good chart, but one that uses some kind of FPU benchmark 
would be the start.  In the end, I did not need to get that far.  Here's 
the back story...

I skim the 7 bands at 192 Khz, rotating between day/night under 
Aggregator.  With a serious contest event on, I drop back to just the 
5/6 contest bands.

It takes around 400 decoders per band to fully decode a major RTTY 
contest event, assuming you have blocked the FT8 slots which can drive 
decoder counts up pretty high.  Let's say you need two bands for So2r 
coverage, plus the band above and below to watch for openings.  As those 
adjacent bands are typically not fully open even in a solar peak, I 
estimated another 300 decoders would be enough to cover the remaining 
two bands.  So call it 1100 skimmer decoders system capability needed.

An old AMD system with a 945 cpu (4 cores with 4 FPU and about 3.4G) 
would support about 250-300 decoders.  So my initial hunt for CPU was to 
pick something with about 4-5x the FPU capability of the 945.  Very 
scientific so far.

And then reality comes up.  The problem with this theory is that there 
are a lot of FPU benchmarks and I never could find anything to tie a 
given benchmark to it's RTTY skimmer capability through some scaling 
factor.  So in the end, I stopped looking at the FPU charts and just 
took a leap on the 2700x as it was reasonably priced and at least 
similar in performance to the Intel 6-core I was looking at.

Turns out that was a very fine pick.  Don't think I have seen the CPU 
utilization over 45% in any of the contests in the last year.

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

On 6/5/19 12:00 AM, Bob Wilson, N6TV wrote:
> On Tue, Jun 4, 2019 at 9:19 PM Jeff Blaine <KeepWalking188 at ac0c.com> wrote:
>
>> 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.
>
> So how do we look that up?
>
> 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.
>
> I found two "AMD 2700x" processors listed here:
>
> https://www.cpubenchmark.net/cpu_list.php
>
> AMD Ryzen 7 2700X
> <https://www.cpubenchmark.net/cpu_lookup.php?cpu=AMD+Ryzen+7+2700X&id=3238>
> Passmark  16982
> AMD Ryzen 7 PRO 2700X
> <https://www.cpubenchmark.net/cpu_lookup.php?cpu=AMD+Ryzen+7+PRO+2700X&id=3292>
> Passmark
> 17161
>
> Which must mean they are about 70% faster than the Intel i7-7700 3.6 GHz
> that I'm using.  How many bands are you skimming for RTTY?
>
> 73,
> Bob, N6TV
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