Thursday, October 28, 2021

Recipe for Success: What is RTTY?

Radioteletype or "RTTY" is a digital data mode that allows text to be sent over radio and has been around since the 1930's.   

Before RTTY signals were sent over wireless, teletype was used going back to the mid 1800's which makes this one of the oldest modes of non-spoken communication, just like Morse Code.

Within amateur radio, RTTY is commonly sent on HF bands by using 45.45 baud at 170 Hz shift width along with a mark frequency of 2125.  It is also possible to use RTTY on all other bands such as the popular 2m band and at even greater speed. What does this all mean?  Lets find out.....

RTTY Basics

The term "baud rate" is used to explain how many words per minute can be sent and there are 60 (45.45 baud), 67 (50 baud), 75 (56.25 baud) and 100 (75 baud) options as standard within amateur radio.  

Here is where sending large amounts of data really started thanks to RTTY since even trying to speak more than 60 words a minute may be a challenge for many people.

If you think about how that translates to 1200 baud which is what APRS uses, or the last generation of "dial up internet modems" in the late 1990's which used 56,000 baud and now, all the way to modern broadband which would be too fast to even easily think about, RTTY sounds pretty interesting, right?

Some of the earliest RTTY activity took place just down the Hudson River on Long Island and a brief history is available on the RTTY Wikipedia page.  Lets keep building on our regional history by keeping RTTY alive! 

Here is what a RTTY signal would look like and how the "mark" and "space" are visualized.

Each of the signal peaks are one of opposing tones that help identity bits in the symbols being sent which translate to letters, numbers and special characters.

While there are more efficient modes of "keyboard to keyboard" communication available today, RTTY is not only reliable, but easy to be sent with basic equipment.

We learned with SSTV experimentation during the weekly UNDR Net in September 2021 over the 146.805 MHz repeater operated by the Overlook Mountain Amateur Radio Club, its possible to send images, so now its time to send some text.

RTTY takes up around 250 Hz of receiver bandwidth if your radio is set for 170 Hz shift between the high and low tones. This is more than ok if you plan on sending RTTY over FM since a typical signal is 25 kHz wide, so there is more than enough room to send RTTY over FM.

The year 2021:  Why RTTY?

While RTTY is mainly used during special contests or between just a few friends, its still a mode that is worth keeping in your communications tool box.

A benefit of audio frequency shift key (AFSK) based modes is that they are easy to decode simply by holding a smartphone near your radio speaker. You can even send RTTY by holding the microphone of your radio near the speaker on your smartphone.

Better results can be had with a wired interface like the Easy Digi device for use with most any handheld radio or the Masters Communications Model RA-40

Some radios even include a built in decoder for RTTY like the Icom IC-7000, IC-7100 and IC-705. 

As we learned by sending the PD50 SSTV mode which takes about one minute over FM,  this should mean we can send at least 60 words of text or more in the same time using RTTY.  This capability could be very useful in certain situations where accuracy counts and a digital signal is better than speaking.

What if we wanted to share Uncle Grants Field Day Chili recipe over the air?  

According to the below photo courtesy of the ARRL, this recipe page has 313 words and it may actually be quicker sending a recipe like this over RTTY compared to multiple smaller sectional photos sent over PD50 SSTV or one higher resolution photo using the PD290 SSTV which would take almost 5 minutes!

The above recipe can certainly be condensed and reformatted for more "human readable" reception if sent over RTTY.

This will be one of our first tests in sending some interesting information using RTTY in the month of November during the UNDR Net.

If you are interested in joining our experiments, feel free to come up with your own interpretation of the above recipe and lets see who can transmit it the fastest that is human readable on the receiving end. 

Please join us every Tuesday at 8:00 PM Eastern US time in the month of November to listen in or participate with what we are doing each evening with RTTY.

IMPORTANT:   Starting December 6th 2021, UNDR Net will be moving to Monday 8:00 PM 

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