[RTTY] 160m in RTTY Contests

[Kok Chen]

On Nov 1, 2009, at 11/1    10:36 AM, Jeff Blaine AC0C wrote:

> One of Chen's earlier comments closed with essentially - do it (a  
> contest)
> and then we would have data.

Remember to include extra diddles or LTRS shifts if your software has  
the capability.  That is the easiest way to detect if, and how much,  
echo is present.  A LTRS character consists of a short Space tone  
(start bit) followed by a long Mark tone (5 data bits of all ones  
followed by the stop bit.

A LTRS character makes a good sounder pulse as long as the echo is  
less than 50 ms long.

Sending two LTRS in a row will allow us to identify any pre-echos (a  
weaker signal that arrives before the main signal), although we might  
be able to guess it by looking at the tail of a single LTRS character.

This is probably the time to also mention the "V" that we often see on  
RTTY.  Those are almost certainly caused by multipath signals since a  
V is a Baudot 11110 and a LTRS is a Baudot 11111.  You don't see it as  
often in contest exchanges as during real DX QSOs where the op pauses  
his or her typing (i.e., diddles get transmitted).

I first became conscious of this problem many years ago when we (in  
California) were seeing strings of VVVV from a DX station.  One local  
RTTY op (who shall remain unnamed :-) broke in on top of the DX and  
sent something like "what is with all the Vs" :-).  I then noticed  
that a V never replaced any of what the DX was actually typing.  It  
simply was a bunch of extra V sprinkled in his text.  It finally  
dawned on me what was happening.

If you start printing sporadic V characters, you can pretty much  
assume it is a strong echo delayed by 7 to 20 ms.

You will not find me transmitting in an 160m RTTY contest, but I will  
definitely try to use it as a opportunity to listen and learn.

BTW, to a potential organizer of a 160m RTTY contest: it might be  
worth accepting SWL logs.  There could be folks who might not be able  
to transmit on 160m (including from some DX countries) but we can all  
receive the stronger signals.  They can provide useful information in  
the Soapboxes; e.g., whether or not they can print all the signals  
that are audible over the noise.

73
Chen, W7AY