[RTTY] More on the KH6ZM mystery

[Kok Chen]

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