Digital Modes…

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Hello again and thanks for coming back to my blog. If this is your first time seeing my blog, please check out my previous posts. I hope you will find some good information. Our topic for today is digital modes. The one thing that all digital modes have in common is the use of a computer interfaced with a radio. While I was doing research on this topic, since I’ve only had first hand experience with VHF digital modes, I realized that there is a lot of different methods that I had never heard of. I have been a ham since 1995 and I consider myself a fairly educated person in the areas of ham radio, but I’ve learned since I started writing this blog that I have barely scratched the surface of what can be done with ham radio. That being said, let me say that some of this stuff that will be in this post, I have no clue about currently, therefore, it is going to be just a general overview. I am going to put some of these things on my to do list for future posts.

So first off lets talk about HF digital modes. First off, let talk RTTY. RTTY or “Radio Teletype” is a FSK mode that has been in use longer than any other digital mode (except for morse code). RTTY is a very simple technique which uses a five-bit code to represent all the letters of the alphabet, the numbers, some punctuation and some control characters. At 45 baud (typically) each bit is 1/45.45 seconds long, or 22 ms and corresponds to a typing speed of 60 WPM. There is no error correction provided in RTTY and as such noise and interference can have a seriously detrimental effect. Despite its relative disadvantages, RTTY is still popular with many radio amateurs. 

PSK31 is a relatively new digital mode and is the first new digital mode to find popularity on HF bands in many years. It combines the advantages of a simple variable length text code with a narrow bandwidth phase-shift keying (PSK) signal using DSP techniques. This mode is designed for “real time” keyboard operation and runs at a 31 baud rate. At this speed it is only fast enough to keep up with those that have a slower typing speed, say around 25wpm. PSK31 enjoys great popularity on the HF bands today and is presently the standard for live keyboard communications. Most of the ASCII characters are supported. A second version having four (quad) phase shifts (QPSK) is available that provides Forward Error Correction (FEC) at the cost of reduced Signal to Noise ratio.

On the older end of digital modes stands Amtor. Amtor is an FSK mode that is hardly used by radio amateurs anymore. Even though it is a robust mode, it only has 5 bits and can not transfer extended ASCII or any binary data. With a set operating rate of 100 baud, it does not effectively compete with the speed and error correction of more modern ARQ modes like Pactor.

Pactor is an FSK mode and is a standard on modern Multi-Mode TNCs. It is designed with a combination of packet and Amtor Techniques. Although this mode is also fading in use, it is the most popular ARQ digital mode on amateur HF today and primarily used by amateurs for sending and receiving email over the radio. This mode is a major advancement over AMTOR, with its 200 baud operating rate, Huffman compression technique and true binary data transfer capability.

There are several other types of HF digital modes, but these I believe are the common ones. I may be wrong since as I said above, I’ve never really dived into HF Digital modes very much. In all honesty, I haven’t used HF very much, other than on like Field Day or other special events. Maybe one of these days, I will, maybe once I’m able to have a ham station at my house again.

Anyway, lets move on to VHF Digital Modes. I guess lets start with Packet. Packet radio started in the mid 1960s. It is basically the amateur radio version of the internet in a manor of speaking. The same basic hardware exists in both. A TNC replaces a phone modem, the telephone is replaced by a amateur radio and the phone line is replaced by amateur radio waves. Packet has three great advantages over other digital modes: transparency, error correction, and automatic control. It is transparent as to when you connect to another station and type a message, it is automatically sent. Error correction is done with every packet of information that is sent. The receiving stations says, “This is what I got”, the sending station says “Yep that’s right” or “Nope, not right, here’s the correct information”

Packet radio is faster than the HF modes we have talked about before, with its ability to connect at 9600 baud, but its limited to basically line of sight transmissions unlike its HF cousins. There are/were packet networks set up that were used to extend the range of a single user. Whether they are still up anymore, I can’t say. While I did use this mode before, I haven’t used it in a LONG time. With the birth of Automatic Position Reporting System(APRS), packet radio as it was has pretty much fallen to the way side.

APRS, is in the fore front of digital modes now. It still uses the same basic protocols and methods that packet radio used, but its main function is position reporting. APRS is used for tracking storm spotters in the field, relief/repair vehicles during a race and just a casual, “here I am.” As an added bonus, information that is shared over the air, can be sent via the internet to a website and displayed for everyone/anyone to see. Check out http://aprs.fi to see APRS in action. Another function of APRS, is you can hook a weather station up to your computer and send out weather data for others to see.

I think that pretty much gives you a wide spectrum of information as to what digital modes are in ham radio. There are a few of these topics, that I would like to dig into a more in a later posts so I look forward to you coming back and checking it out then. I hope that you got a little bit of information about digital modes at least. Maybe enough that it peaked your interest in some of these methods and you will try them out for your self.

So as usual, please bookmark my blog and like my new facebook page, Everything Hamradio, and please share by posts with your friends. I guess that pretty well wraps it up for this post. I hope that you will check back later for more posts about this wonderful hobby called ham radio.

73 de K5CLM

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