[RTTY] Audio Card Reccomendations

[Kok Chen]

On Mar 8, 2009, at 8:40 PM, Darl Deeds wrote:

> I use mine for PSK, RTTY, CW and Feld Hell. It works great for that  
> usage with no problems for me, but I am not an expert so I am sure  
> that there are limitations for others.

If you use Feld Hell, you will have to turn on some diddle in  
software, otherwise the first part of a character will be missing at  
the receiver's screen when you pause your typing long enough for the  
VOX of the SignaLink to disengage (i.e., every time the red LED  
extinguishes).

When you start typing again, the VOX takes a short time before it  
kicks in to key the transmitter, so the person who is trying to copy  
you will see a small missing portion at the leading edge of the next  
glyph.  The VOX turn-on delay has to be much less than 8 millisecond  
for the first glyph to be visually close to perfect (each pixel of  
standard Feld Hell is 8.136 ms in duration).

Many Feld Hell implementations therefore has an optional "diddle" to  
keep the VOX alive.  Often, this is in the form of periodically sent  
full-stop (period) characters.  You send enough diddles per second to  
keep the VOX engaged until you change back to receive mode.

If you are using FM Hell, this is not a problem since FM Hell modes  
are 100% duty cycle.  The VOX does not disengage when you pause typing  
to FM Hell.

Similarly, if you are using J2A for Morse transmission, the first part  
of a dit (or an entire dit, if you operate fast enough CW) will be  
missing if the PTT disengages and reengages.  With HSCW, characters  
could be missing before the VOX driven PTT has time to engage.

With hard PTT, this does not happen because the software that you are  
using will key the PTT line down before it transmits any information.   
It will keep the PTT keyed down until you are ready to go back into  
receive mode again.

73
Chen, W7AY