[RTTY] Decoder performance on crowded bands

[Pete Smith N4ZR]

Jeff, I'd be interested to know to what you attribute the reduction in 
the number of S&P mis-spots.  Is it simply because with many Skimmers 
spotting this year, the chance of someone mistakenly spotting any given 
S&Per as CQing becomes more likely?

Rather than running your own Skimmer, people could (through ARC V6) 
limit spotters to nearby stations and then apply the CT1BOH Skimquality 
filters for further quality control.  One of the things I really like 
about them is that you can either just *see* the evaluation on-screen or 
actually use it as a filter - so, for example, you could filter out 
everything that is not spotted the same way by 3 or more Skimmers 
worldwide, while still only actually seeing the spots coming from people 
near you.

73, Pete N4ZR
Download the new N1MM Logger+ at
<http://N1MM.hamdocs.com>. Check
out the Reverse Beacon Network at
<http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.

On 9/28/2015 3:48 PM, Jeff AC0C wrote:
> Don,
>
> I ran Alex Skimmer Server on a local QS1R in the WPX earlier this year 
> and the results were hard to believe.  Performance was exceptional.  
> And the benefit is that 100% of the spots are workable because they 
> come off your local system.  I had almost zero in the way of S&P 
> mis-spots.  The downside to this configuration is that you need the 
> QS1R ($$) and if you want to skim multiple bands in their extents (96 
> Khz x 3 active bands), you literally need the best Intel chip 
> available (more $$).
>
> 73/jeff/ac0c
> www.ac0c.com
> alpha-charlie-zero-charlie
>
> -----Original Message----- From: Don AA5AU
> Sent: Monday, September 28, 2015 2:42 PM
> To: Tim Shoppa ; rtty at contesting.com
> Subject: Re: [RTTY] Decoder performance on crowded bands
>
> Tim wrote:
> "The frequency resolution and accuracy seems to have improved in the 
> skimmers in the past few years and often times I would click on a spot 
> and be tuned within 10Hz, that is great!"
> Yes, indeed. I found the frequency accuracy of skimmer spots to be 
> excellent. I had ALL the RTTY skimmer spots coming in this weekend and 
> it was amazing to see the spots flying in at a pace that seemed like 
> well over a hundred spots a minute.
> Unfortunately, IMHO, the RTTY skimmer still needs a lot of work. I 
> would prefer to see less skimmer spots so that there are less S&P 
> stations are being spotted and less busted calls spotted. It seems I 
> got spotted quite a bit when I was S&P. This means that other S&P 
> stations are being spotted as well. This means that a MAJORITY of the 
> spots are not valid run stations. This is not good. I understand there 
> will always be some busted calls but hopefully work is being continued 
> to make this better. There was one particular skimmer that seemed to 
> bust the start of calls and this caused a LOT of spots to show up as 
> new multipliers. For the most part, I knew the calls were busted but 
> it seemed I was continuously clearing bogus calls from my new 
> multiplier list. I nearly blacklisted this one skimmer, and that's a 
> solution, but I was afraid I'd miss a new multiplier! HI
> I am grateful for the time, effort and resources from the entire crew 
> of skimmer ops. They are doing great work and need to be commended. 
> This was the first time I've used the RTTY skimmer spots for a full 
> contest and it was very useful. It will take some thinking to 
> determine the best options for using this new tool.
> When using non-skimmer spots, you can nearly rest assured that a 
> station spotted is a run station and you can chase them. The only real 
> problem with that is knowing whether or not the spotter was using FSK 
> or AFSK and if the spotted station is on the frequency of my radio 
> when I go there. With the skimmers, that problem appears to be 
> eliminated (when using fFSK) and it's a great thing.
> But now you can't just click on spots because most spots are NOT run 
> stations. My solution, for now, is to run two separate packet windows 
> (not sure this is possible with WriteLog on a single PC but I did it 
> on networked PCs this weekend since I was single band). One packet 
> window will receive skimmer spots and the other non-skimmer spots. Use 
> the skimmer spots to populate new multipliers to a Packet Spots window 
> and use the non-skimmer spots to populate the bandmap. It may take 
> some work from software authors or there may be solution already out 
> there I don't know about?
> 73, Don AA5AU
>
>
>
>
>      From: Tim Shoppa <tshoppa at gmail.com>
> To: rtty at contesting.com
> Sent: Monday, September 28, 2015 9:25 AM
> Subject: [RTTY] Decoder performance on crowded bands
>
> Wow, there was a lot of activity for CQ WW RTTY! 20M and 15M were filled
> completely between 080-150kc above band edge,
>
> The "bottom ends" of the band were particularly crowded.
>
> I used 3 decoders simultaneously - MMTTY, 2Tone, and Gritty. I don't 
> always
> run Gritty for the more minor contests, but I did fire it up for CQ WW 
> RTTY.
>
> MMTTY is still my "main decoder". It decodes just a little faster than 
> the
> other decoders and handles the broadest range of senders.
>
> 2Tone did spectacularly well in decoding in the presence of strong 
> adjacent
> signals. This was particularly important on 40M and 80M where all the DX
> usually had a strong adjacent local CQ'ing. It did not do so well with 
> some
> of the "slow RTTY" signals. 2Tone AFC always did "what I wanted" and 
> helped
> with a couple of off-frequency replies.
>
> 90% of the time I was looking between MMTTY and 2Tone.
>
> Gritty did very well decoding in the presence of flutter and other 
> unusual
> effects, pulling out callsigns from flutter on 10M and the odd stuff that
> happens on 40M at sundown.
>
> Very shortly after the start of the contest I set my receiver 
> bandwidth to
> about 1200Hz because 2Tone and Gritty work best like this. If I set my
> bandwidth too narrow it seems that Gritty just stops working. I also 
> turned
> IF gain way down so AGC wouldn't pump. Only a few times did I narrow 
> up my
> receiver bandwidth.
>
> While I was not looking at the Gritty decoder all the time - I was always
> looking at the Gritty waterfall. The Gritty waterfall is very very 
> useful.
> The color-intensity range and scroll rates work very well.
>
> I happened to enter assisted as well. I started with VE7CC cluster and 
> its
> default skimmer filtering but it was not letting all the skimmer spots I
> wanted through. Even though the calls were being spotted by 3 or 4
> skimmers, lots of time they were not getting through whatever additional
> checks were enabled in VE7CC cluster. So I went straight to
> reversebeacon.net and took the full brunt of the firehose. It was obvious
> not all the skimmers covered all the RTTY band - some (especially EU)
> seemed to only be skimming in the 080-100 segments. But others were
> skimming all the way up to 150kc above the band edge and those proved 
> very
> useful because activity was just huge this weekend! The frequency
> resolution and accuracy seems to have improved in the skimmers in the 
> past
> few years and often times I would click on a spot and be tuned within 
> 10Hz,
> that is great!
>
> Again, thanks to the authors of all these wonderful decoders, and the
> skimmer guys.
>
> Tim N3QE
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