Getting Started on RTTY - Page 7
Setting Up MMTTY to run FSK
With FSK, you
are not concerned about audio coming out of the sound card. You must key
the FSK input to your transmitter with an interface circuit connected to a
serial COM port using either the simple transistor circuit shown below or some
other type of circuit. Many operators use opto-isolator transistors or IC
circuits to key FSK and PTT from a COM port. Some commercially sold
interfaces also include an FSK keying circuit (see Page 9). The choice of
interface circuit is up to you. I've had great success with the simple
transistor circuit. The advantage of opto-isolators is electrical
isolation between COM port and radio. This may be helpful if you
experience RFI or to protect the PC or radio in the unlikely event of a
lightning strike. To eliminate RFI on my cables between computer and
radio, I use ferrite or iron powder rods or toroids on nearly all my
cables. Click here for my RTTY RFI
page.
With FSK you have two necessities - FSK & PTT. With PTT,
you have three choices. You can either build another circuit identical to
your FSK circuit (for a nice packaged interface, check out the one built by Ron,
ND5S, here), use a commercial interface, or use Radio Command within
MMTTY. With MMTTY, if you are going to key PTT with an interface, you
must use the same serial COM port for both FSK and PTT. And you set
this COM port on the TX Tab of MMTTY Setup as shown here.
The "PTT port" setting on the TX tab is actually for both PTT and FSK. If you use Radio command for PTT, you still must set the "PTT port" setting to the serial port where your FSK interface is connected. In the example above, the FSK interface is connected to COM3 regardless of how PTT is activated.
Once the "PTT port" is set to the serial port connected to the FSK interface, go to the Misc tab of MMTTY Setup. Here you must set the "Tx Port" to "COM-TxD (FSK)". Click OK and go back to the main MMTTY screen. Once the physical FSK connection is made to your transceiver, you are now ready to transmit FSK.
