I recently competed in the CQ WPX RTTY Contest. Well, I say “competed,” but the truth of the matter is that I wasn’t remotely in danger of winning the contest. This was my first time working with RTTY, and I spent much of the contest getting my sea legs and learning how it works.
What is RTTY?
Radioteletype or RTTY, is a digital mode that was first used by the military and newspaper industry in the early 20th century. As practiced by amateur radio operators, it is a frequency shift key (FSK) mode, meaning that the broadcast signal is comprised of a tone that is sent on one of two different frequencies. The lower of the two frequencies represents a binary 0, while the upper of the two frequencies represents a binary 1. By switching back and forth between the two frequencies at an agreed-upon rate, a radio can broadcast a string of binary data that can be decoded by whomever receives it.
The binary string that your radio sends represents text that has been encoded with Baudot code, a system not unlike Morse code that assigns a five bit representation to each character or symbol. The five bit string is padded with one start bit and two stop bits, which means that in practice, each character is transmitted as an 8 bit byte.
When first invented, a teletype system consisted of three parts: a teleprinter that displayed the messages received by the system, a modem capable of translating text to code and back, and a radio that transmitted code and received code that was transmitted by another party. In modern amateur radio setups, a computer typically acts as both the teletype and the modem, and is connected to a radio via CAT control and/or an audio interface.
Connecting the Radio to the Computer
The Yeasu FT-450D features a six pin mini din port on its back panel that is referred to as the DATA jack. Readers of a certain age will recognize this type of connector as a PS/2 mouse/keyboard jack.
This DATA jack exposes pins that allow external hardware to control the radio for Audio Frequency Shift Key (AFSK) or Frequency Shift Key (FSK) operations.
To connect my computer to this port, I purchased a cable that breaks the GND, DATA IN, and DATA OUT pins out to a pair of 3.5mm audio jacks. The output jack is connected to the input of a USB sound card, and the input jack is connected to the output of the same.
It should be noted that it’s possible to build your own data cable for this radio. I opted to purchase mine, but plans are available for making a similar cable, as well as a more advanced version that can be used for other digital modes.
Configuring the FT-450D
In order to send and receive RTTY via AFSK, you’ll need to tweak a few options on the Yeasu.
Start by pressing one of the BAND buttons until you find the band that you wish to work. The ARRL band plan will tell you where to find RTTY on each. It should be noted that 30m, 17m, and 12m are called WARC bands and cannot be used for contesting.
With your band selected, press one of the MODE buttons repeatedly until the DATA indicator appears on the front panel.
Next, we’re going to dive into some of the options in the F menu. Press and hold the F key until the MENU indicator appears on the front panel, and then turn the DSP/SEL knob to find each option. Press the DSP/SEL knob to select the option, and then spin the knob to change the value of that setting. One final press of the DSP/SEL knob will save your changes. Once finished, press and hold the F key until the MENU indicator disappears.
The following need to be adjusted for each band that you wish to work:
- D TYPE: Change this to USER-L, which will cause your radio to receive and transmit data on the lower sideband.
- DIG VOX: When using AFSK, the radio will automatically begin transmitting when the input audio level exceeds some threshold. The DIG VOX setting adjusts that threshold. Set the output volume on your computer to a reasonable level, start transmitting a RTTY signal, and then increase the DIG VOX value from zero until the radio starts transmitting. When you stop sending the RTTY signal from your computer, the radio should stop transmitting.
- RTYRPOL: This is the polarity of your RTTY signal (i.e. if the lower pitched tone is considered to be a 0 or a 1). You’ll want to set this option to NOR.
- RFPOWER: RTTY is more like SSB than other digital modes. When contesting, you’ll likely want to dial your RFPOWER up to 100 if you want to be heard through the pileups.
- DIALSTP: This one is optional, but because digital modes take up less bandwidth than phone, you may find it useful to adjust the rate at which the tuning knob changes frequencies.
You can find more information about these and other settings in the Yeasu FT-450D manual (PDF).
Installing MMTTY
For my first time out, I chose to use a program called MMTTY as my terminal emulator. CQ WPX RTTY is a contest, and I use N1MM+ as my contest logger. N1MM+ knows how to talk to MMTTY, which should have meant that I would be able to work the contest in a familiar environment similar to the one that I use for SSB contests.
In practice, I was late getting started with the contest, and never did figure out how to integrate N1MM+ and MMTTY. Instead, I opted to log manually, which worked well enough for my first time out.
If you opt to use AFSK and connect your radio to a sound card like I did, you will need to configure MMTTY to use the correct piece of hardware. To do this, select Option > Setup MMTTY, and navigate to the SoundCard tab in the window that appears. Use the radio buttons on this page to select the appropriate hardware for input and output.
One started, MMTTY will attempt to make sense of whatever white noise it hears on the portion of the band that you’re tuned to.
Sweep through the band while keeping an eye on the waterfall display in the top right corner of the window. You’re looking for two peaks in the audio signal that are the same distance apart as the two vertical yellow lines. If you line the peaks up with the yellow lines, MMTTY will be able to decode the signal, and you should start to see legible text appearing in the big text box in the centre of the window.
To transmit, type a message in the lower text box and then hit your F9 key, or press the red TX button in the upper left hand of the window. The transmit button is not a toggle, so you’ll have to click it a second time (or hit F9 again) to stop transmitting once your message has been sent.
Finally, if at any time you see the word “Overflow” in the top right corner of the waterfall display, that’s an indication that the audio signal from your radio is too loud. Turn down the input volume on either your external sound card, or in the Windows sound panel until the message disappears.
What’s Next?
This coming weekend, the North American QSO Party RTTY contest (PDF) is taking place from 1800 UTC on February 27 to 0600 UTC on February 28. I intend to use this contest as an excuse to either properly integrate N1MM+ with MMTTY, or to try decoding RTTY with fldigi. Maybe both.
Going forward, I’m hoping to use my newfound skills to play with other digital modes. I may even try to contribute some code to one of the many open source projects that are maintained by hams who play on this part of the band plan.
Until then, 73.
