[RTTY] Decoder performance on crowded bands

Mon Sep 28 17:09:40 EDT 2015

One potential step toward improved RTTY Skimserv results is to use the 
CT1BOH "skimquality" filters available through AR Cluster V6. See 
<http://reversebeacon.blogspot.com/2013/12/a-new-tutorial-on-using-rbn.html>, 
about halfway down.

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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