[1000mp] RTTY

[Joe Subich, W4TV]

Tad,

> One thing I had to do was reverse the RTTY  polarity
> on the MKV-- It is menu setting 6-1 on the MKV.  I'm
> still not clear about why this was but initial I was
> getting reports that I was "upside-down" and when I
> changed this setting everybody was able to copy me.

RTTY (FSK) calls for the MARK to be the higher of the
two RF frequencies.  The FSK input can have two states
"open" and "closed."  Open is generally a logic "high"
(1) and closed is generally a logic "low" (0).

In the BAUDOT code a mark is a logic high (1) and a
space is a logic low (0) and that is what comes out
of the serial port when you transmit RTTY.  However,
the RS-232 levels (+12V high and - 12V low) are not
compatible with the FSK input on most transceivers.
In order to interface with the transceiver, most
terminal units use a single transistor or optoisolator
to convert the +/- 12 volts to "open" and "closed."

A single transistor or optoisolator "inverts" the logic
state on its output.  Thus a +12V input (a "high")
will result in a "closed" condition (a "low") to the
transceiver.  Yaesu accommodates this by providing
the "Reverse" option at menu 6-1.

73,

    ... Joe Subich, W4TV
        microHAM America, LLC.
        www.microHAM-USA.com