[RTTY] More on the KH6ZM mystery

[Jim W7RY]

I have him on 20 and 40 as KH6ZM.
73
Jim W7RY


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From: "Kok Chen" <chen at mac.com>
Sent: Tuesday, January 11, 2011 8:39 PM
To: "RTTY Reflector" <RTTY at contesting.com>
Cc: "Alex Malyava" <alex.k2bb at gmail.com>; "Mark n2qt" <n2qt at verizon.net>
Subject: Re: [RTTY] More on the KH6ZM mystery

> Gotcha!
>
> As a last resort, I took a look at the waveforms :-).
>
> Very clean signal, as I told Alex in an email earlier.  In the recording 
> the KH6ZM had almost 20 dB SNR in the noise bandwidth that Alex uses. (I 
> can only wish I have a receiving antenna like that!)
>
> I can see that KH6ZM used 1.5 stop bits.  And the "Z" of KH6ZM was clearly 
> there, every single bit [sic] of it.
>
> And then it gets interesting...
>
> He sends a start bit followed by 2 more zeros for the least significant 
> bits, then followed by 1.86 bits of ones.  And then cuts off.
>
> So he was basically sending ?1100 and no stop bit, instead of 11100. 
> (Remember, least significant bit gets transmitted first -- typical of 
> UARTS.)
>
> He is chopping off his stop bit and 1.14 of his data bits.
>
> I do see some low level signals afterwards, but too low inside the noise 
> floor of the sound file (Alex' recording was down 25 dB from full scale 
> sound card level).  It is possible that the west coast is hearing his 
> barefoot signal after his linear turned off too early, and the east coast 
> could have copied him if they had matched the sound card gain to the 
> signal.   Maybe.
>
> I don't use amplifiers, do people sequence their amps this way for RTTY?
>
> Anyway, people should at least copy him as KH6Z (but not as "KH6M") since 
> the entire Z was cleanly transmitted.  But the last character is 
> definitely ill formed.
>
> The ARRL contest robot is going to have lots of fun with this one :-).  I 
> wonder if it gives points to one or both sides if the call is incorrectly 
> copied at one end.  Personally, I would give credit to everyone who copied 
> him as KH6Z* where * is anything including null, since that is what I see 
> in Alex' sound file.  Unfortunately, the robot don't look at sound files 
> and you have to log what you copied.
>
> 73
> Chen, W7AY
>
>
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