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Re: [RTTY] ST0R RTTY Statistics

To: RTTY Reflector <rtty@contesting.com>
Subject: Re: [RTTY] ST0R RTTY Statistics
From: Kok Chen <chen@mac.com>
Date: Thu, 11 Aug 2011 09:09:37 -0700
List-post: <rtty@contesting.com">mailto:rtty@contesting.com>
On Aug 11, 2011, at 8:02 AM, Joe Subich, W4TV wrote:

> With nearly three times as many CW QSOs as RTTY (Digital) QSOs and
> five phone QSOs for every two RTTY QSOs, there is still a long way
> to go before major DXpeditions are giving RTTY more than "lip
> service."

I suspect this will improve as DXpeditions adopt better tuning techniques for 
RTTY.  IMHO.

With CW, you can listen for signals and decode a signal that are a full kHz 
away (guys like N5KO use the filters in their own brains for CW; Trey's advice 
to me was to call away from a CW pile if I know that he is the op at the DX 
end).  

With voice, you make use of the "cocktail party effect" (the term is actually 
used in technical papers, see also here 
http://en.wikipedia.org/wiki/Cocktail_party_effect).  

You cannot do either in RTTY if you are tuning with a VFO knob.

If the pile is heavy on the previous RTTY QSX, it could take a bit of waiting 
for a call to appear cleanly on the DX's screen, or for a really large signal 
to override everyones power combined (like the FM "capture effect," but with 
one station against the power of many stations combined, versus one station 
against one other station), or having to retune slowly using the VFO knob.  
None of this is especially fast.

If the DX uses an RTTY skimmer, or a waterfall with memory, they could find a 
station far away from the pile to work.  Just find the first station that is in 
the clear within a 20 kHz (or however wide the receiver can tune) passband to 
work next.

You can imagine that for CW, you are instantaneously working with a 2 
dimensional field (time and frequency).  With a traditional way of tuning RTTY, 
it is one dimensional (time only).  But you gain back the advantage compared to 
CW when you use a skimmer or memory-buffered waterfall tuning (standard 
waterfalls won't give you that of course). 

All digital modes are machine decoded today anyway, so you might as well take 
advantage of that fact to pull out one signal from among many signals.  
(Whether you prefer to call it RTTY or something else -- the technology today 
that people use for keyboard modes is far different from the "RTTY" that was 
used with mechanical teletypes; the only similarity to real steam powered RTTY 
is the use of two FSK carriers, a shift of 170 Hz and a baud rate of 45.45 Hz.  
And if you don't write your own software to do the demodulation, that 
distinction between the different digital modulation modes is blurred even 
further.)

Bear in mind that dynamic range is not so big a problem if you are the DX.  
They can polish off all the large signals first before working their way to the 
weaker ones.  The limitation of being able to concurrently decode RTTY signals 
whose signal strengths are separated by "only" 10 or 15 S units is not a 
problem.  At some point, that weak signal that is barely above the noise floor 
is going to be within 10 S units of the loudest signal present at the time.

Once a DXpedition adopts wideband, agile tuning for RTTY, we too would have to 
change our pileup busting behavior.  The key is to look for an empty hole, no 
matter how far away from the previous QSX it is.  That has already been shown 
to be true with 9X0TL.  In Tom's Quicktime video, you can also watch 9X0TL 
clear out the strongest signals first but eventually get to the weak ones.

I don't myself really look forward to that progress (where the DX can pick you 
off quickly as long as you are above the FSK decoding threshold with respect to 
their noise floor).  Working DX becomes "shooting fish in the barrel" and the 
challenge goes away.  How hard anyway is it to find an empty bandpass to 
transmit.  He eventually finds you.

BTW, the above scheme also applies to working a DX that is "begging" in an 
almost empty subband where you have no idea what his QSX is.  Today, you have 
to wait for him to slowly tune across you while you are calling.  If you are 
weak, he will usually miss you completely if he is not a seasoned RTTY operator 
(this happens to me so often that I prefer to let the DX find a strong station 
first and then call next at that frequency; the strong station acts as a beacon 
for the inexperienced RTTY op to hone in on).  With a skimmer or waterfall at 
his end, he will notice you the instant you transmit.  

The skimmer allows inexperienced ops to be pretty much as effective as the 
experienced ops -- is that what we want eventually?  (Even a child can use a 
cell phone.)

73
Chen, W7AY

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