FSK RTTY

Introduction

Operating RTTY and especially RTTY contesting has quickly become my favourite facet of amateur radio. I started operating RTTY in 1984 using a Dragon 32 (6800 CPU) computer and G4BMK software and Terminal Unit. My interest then waned until 2002 when I discovered MMTTY and N1MM. This software combination has made RTTY contesting a point and click operation and combined with the increase in RTTY operators can create high QSO rates during contests.

AFSK RTTY

I initially operated RTTY using AFSK with a Rigblaster Nomic interface to an Icom IC-756 Pro transceiver. Using AFSK meant that I could not use the Icom's RTTY filters and QRM during contesting meant that I generally operated rather high in the RTTY sub-bands.

FSK RTTY Attempt 1

Recently I decided to try FSK RTTY and then found out that my Rigblaster Nomic could only work with AFSK. Fourtunately K5WW has very clearly described how to modify the Rigblaster Nomic to allow FSK to be used. The modification is a single transistor and resistor and was easy to add. However, I was unable to get the PTT switching to work using the COM port on my Dell laptop probably due to low levels as using a desktop PC's serial port everything worked well. Running FSK I was able at long last to use the Icom's RTTY filters (5 of them - 1 kHz, 500Hz, 350 Hz, 300 Hz and 250 Hz) along with the wonderful Twin APF filter which literally brought RTTY signals out of the noise. I am very impressed by the Icom's RTTY filters.

FSK RTTY Attempt 2

Frustrated at not being able to use my laptop I spent some time looking around the Internet. I found that Mako-san, the MMTTY author, had released COM-FSK which allows MMTTY to perform FSK keying using USB to Serial devices and also the Parallel Port. To use the Parallel Port for FSK Oba-san, JA7UDE, has provided an example Parallel Port interface circuit (reproduced below):

I replaced the Japanese NEC 2SC945 transistors with 2N4401 devices. The components easily fitted into the Parallel Port shell. For the Icom IC-756 Pro the connections to the transceiver were as follows:

To enable Parallel Port FSK keying with MMTTY on Windows 2000 or XP it is necessary to do the following:
If you are using Windows 95/98 or ME then steps 3,4 and 5 can be skipped.

  1. Download the COM-FSK MMTTY extension

  2. Extract extfsk.dll and place the DLL in the same directory as MMTTY

  3. Download DLPORTIO which allows COM/LPT ports to be used under Windows 2000 and XP

  4. Extract the following three files from the dlportio.zip file into the same directory as MMTTY:
    Dlportio\dll\TDLPortIO.dll
    Dlportio\DriverLINX\drivers\DLPORTIO.dll
    Dlportio\DriverLINX\drivers\DLPORTIO.sys
    (note that this step is still required even if you have already installed DLPORTIO for N1MM)

  5. Reboot the PC

  6. Run MMTTY and from the MMTTY setup window enable FSK keying from the "Misc" property page by selecting the "Com TxD (FSK)" radio button as below

  7. From the "TX" property page select "EXTFSK" from the "Port" drop down menu as below

  8. Close the MMTTY setup window. The EXTFSK window will then appear as below. Select "LPT1" as the Port. If "LPT1" does not appear in the drop down list then another reboot is required

  9. With the JA7UDE Parallel Port interface circuit I configured EXTFSK "LPT1" to use Pin 2 (D0) of the Parallel Port as the FSK output and Pin 1 (Strobe) of the Parallel port to control PTT

Using the IC-756 Pro I found that I had to invert the PTT keying using EXTFSK to key the transmitter correctly. Otherwise, the Parallel Port FSK keying works great and frees up the serial port for PC to transceiver communication as well as working with laptops that do not have a serial port.

< Return to G4ZFE