[RTTY] Decoder performance on crowded bands

Tim Shoppa tshoppa at gmail.com
Mon Sep 28 10:25:41 EDT 2015

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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