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
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