[RTTY] FSK and CAT via 1 serial port

[Don AA5AU]

I believe what you say is probably true about CAT using TxD.  And yes, FSK is "traditionally" keyed on the TxD line of a serial port.  However, it can be keyed on other lines as well depending what software you are using.  If you use MMTTY, then you can also key FSK on DTR (and probably RTS but this is sometimes not desireable because RTS is normally used for PTT but you can key PTT via radio control on most radios and use RTS for FSK with MMTTY).  DTR traditionally is used to key CW.  So if you're new interface includes CW keying on DTR, then you can build some sort of switch to move keying to either the CW port or FSK port on your transceiver depending on what mode you are using at the time.
 
In MMTTY, you can change the FSK keying line via ExtFsk (latest version is ExtFsk106), which is a separate plug-in download to MMTTY and can be found on the MMTTY site here:
 
http://hamsoft.ca/pages/mmtty/ext-fsk.php
 
This should also work with most or all programs that use the MMTTY engine, such as N1MM et al.  WriteLog, which uses a 3rd party MMTTY plug-in, also has provisions for keying FSK via DTR along with software-generated through a USB-to-serial adapter.
 
Having said all this, the simplest solution may be to purchase a USB-to-serial port adapter and add another serial port to the computer.  You can then build a simple transistor keying circuit for FSK or purchase a W3YY opto-isolated interface and hang it off the adapter.  The choice is yours.
 
73, Don AA5AU
 
 

From: Louis Ciotti <lciotti1 at gmail.com>
>To: rtty at contesting.com
>Sent: Wednesday, April 27, 2011 12:38 PM
>Subject: [RTTY] FSK and CAT via 1 serial port
>
>Hello,
>
>I am looking for some validation on the information I have gathered via the
>web.  I am working on building up an all inclusive interface box for my
>IC-718 to PC.  It is going to have the sound card interface, CI-V interface,
>CW key, and I want FSK but that is where my question is.  From what I have
>read, FSK via serial port is done by toggling the TX pin.  The TX pin is of
>course also used on the CI-V rig control connection.  Is this correct?  if
>so looks like I will have to have 2 serial ports if I want to use FSK rather
>than AFSK right?
>
>Thanks,
>
>Lou
>K2LRV
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