Getting Started on RTTY

Getting Started on RTTY - Introduction

Everyday more and more Amateur Radio operators are operating on the HF digital modes, in particular, RTTY. In each RTTY contest I operate, I find about 8-10% new calls that I've not seen before. There are several reasons for wanting to be a RTTY op. No matter what that reason might be, it is the purpose of these pages to assist getting you started on RTTY.

Even though I've been active on RTTY for over 20 years, have won several RTTY contests and have achieved RTTY DXCC Honor Roll, I don't claim to have all the answers. I do have a technical background and am familiar with many of the technical aspects of operating RTTY. RTTY is the most fun I've had in over 30 years of Amateur radio. It can be both complicated and simple. So I'll try to keep things simple.

Anyone can operate RTTY. You don't have to know how to touch type to run RTTY. Hunt & peck works fine. Every program I know for RTTY includes special "buffers" which hold pre-typed messages that can be sent by pressing a function key or clicking a button on your screen with a mouse. The late Junior, previously N5JR (this call has since been re-issued to Joel Rubenstein who is an active RTTY operator too), was a paraplegic and earned RTTY DXCC before he died. He operated RTTY with a stick in his mouth. He should be an inspiration to all of us and shows that even those with disabilities can enjoy this very fun and exciting mode. There's really no excuse not to try.

Whether you desire to operate RTTY for DX'ing, contesting or ragchewing, you have to start somewhere. It's my hope that I can point you in the right direction. From there you will be able to make your own decisions on how you want to operate RTTY from your station.

RTTY is Baudot code (see http://chem.ch.huji.ac.il/~eugeniik/history/baudot.html for excellent information on Mr. Baudot and his code). More specifically, on the Amateur HF bands, it's 5 bit baudot meaning that every character consists of five bits, either mark or space (in actuality Baudot is 8 bits because a start bit and two stop bits are added for synchronization see http://www.aa5au.com/gettingstarted/rtty_diddles_technical.htm). In general, a baud rate of 45.45 baud is used on HF. 45.45 baud is the equivalent of 60 wpm. Even though 45.45 is standard, you will occasionally come across a RTTY signal at a different speed. Ed, P5/4L4FN, preferred to run 50 baud rate (66 wpm) when he was active on RTTY from North Korea. 75 baud (100 wpm) can also be used on the Amateur HF bands.

The standard mark and space tones are 2125 hz and 2295 hz respectively. These frequency tones are also referred to as “high” tones. Although these standard tones are used by most Amateurs, it's possible to operate RTTY using other frequency tones. This is fine as long as you maintain the standard 170 hz shift (2295-2125 = 170 hz). Some commercial TNC's such as the KAM and PK232 use a 200 hz shift when running AFSK. Although 200 hz shift will work OK, 170 hz is standard on HF. Sound card programs will sometimes change the frequency of the mark and space tones when transmitting AFSK while using the NET feature to line up your transmit signal with that of a received station, but they maintain the 170 hz shift. Although that's important to know, I suggest not using the NET feature just yet.

For the purpose of getting you started, MMTTY will be used here as the example program to use for running RTTY. Why? For several reasons. MMTTY is a simple program to use. It's easy to set up and in all the years I've operated RTTY, MMTTY is the best decoder I've ever used. The best part of MMTTY is that it's free! The MMTTY help file has an abundance of information about RTTY in general.

AFSK vs. FSK (Audio Frequency Shift Keying vs. Frequency Shift Keying)

The biggest decision you will make when you begin to set up for RTTY, is whether you want to use AFSK or FSK to transmit RTTY. Either way is acceptable.

There is an excellent explanation of AFSK and FSK in the MMTTY help file so I won't go into a lot of technical detail here. For simplicity sakes, AFSK and FSK are terms to describe how RTTY is transmitted. AFSK is when you send audio from a TNC or Sound Card to the audio input of your transmitter either via the mic input or accessory jack. FSK is when you send on/off keying from a TNC or Serial COM port (with MMTTY you can also use a parallel LPT port to transmit FSK) to the FSK input of your transmitter. Most modern transceivers today have an FSK input. By using the FSK input to your transceiver, you can then operate the radio in the RTTY or FSK position and make use of filters available for receiving RTTY, such as a narrow 250hz or 500hz IF filter. In most cases, when using AFSK, your radio will be placed in the LSB position (although some, especially in Europe, prefer using USB).

I am biased in my opinion of AFSK vs. FSK. I prefer FSK over AFSK all of the time. There are advantages and disadvantages to both. When operating AFSK, you must make sure the audio coming from your TNC or Sound Card is at the correct level and maintain this level. If the audio is too high it will overdrive your transmitter and more than likely result in a distorted RF signal or cause your radio to put out "image" signals across the band. You also must make sure you do not have the speech processor turned on when transmitting AFSK RTTY. This will also cause problems on your RF signal. The only real advantages to running AFSK are that you can get started rather quickly using this method because it's simple audio-to-a-soundcard input for receive and audio-from-a-soundcard output to your transceiver for transmit and you can also make use of the NET features of sound card programs. But personally, I think NET is a nice feature, but it can cause problems when not used correctly. Another disadvantage of using AFSK is that most transceivers will not allow you to use the narrow IF filters in your radio when operating in the LSB or USB positions. Some recently manufactured radios allow you to change the characteristics of your IF filters so you can effectively receive RTTY in the SSB position. Check your manual to see if this is the case for your radio. And if you wonder how your radio works on RTTY, go back to my RTTY Page and find your radio listed under my "RTTY Radios" section.

I prefer FSK because it's straight on/off keying into the FSK input of my radio. I don't have to worry about the audio level or whether I forgot to turn the speech processor off. I can then use the FSK mode on my radio along with the narrow 250 and 500 hz filters. When I switch from SSB to RTTY, I only have to change the mode on my radio. There is a little more work involved when using FSK. If you use a sound card, you must have a spare serial COM port (or parallel LPT port) available on your PC in order to key both FSK and PTT, whereas if you use AFSK, you don't need this extra COM or LPT port and you can use VOX to key the radio. However, if you use MMTTY or any other sound card program to generate AFSK and use VOX to key your radio, any other sound generated by Windows could possibly key your radio and send that sound out on the air. That would not be good. There are ways to keep this from happening and I will explain that as well.

There is more detailed information covering AFSK and FSK on pages 5, 6 and 7 which will help you make your decision on whether to set up for AFSK or FSK RTTY transmission.

Let's get started. The first thing we will do is to download MMTTY from the Web.