Some Amateur Radio Communications Modes

Some of the more common communications modes for Amateur (HAM) Radio

Human to Human

Morse Code, also known as CW - The simplest mode that can utilize a very simple transmitter and receiver. In the early parts of the 20th century, many many Hams built their own rigs from scrounged parts.

Voice - There are several modes used for voice but the two most often used now are SSB (Single Side Band), used on the HF (High Frequency, 1.8MHZ-30MHz) bands and FM, most commonly used on the VHF and UHF bands.

Digital (Computer Communications)

These modes will use a computer hooked to an SSB voice transceiver with a simple interface. Most will work fine even on older tube-type radios. In addition, some of the newer ones like PSK31 and similar, can also use a specialized, usually inexpensive, transceiver dedicated to that mode.

Radio Teletype (RTTY) - This mode is a basic keyboard to keyboard mode that is essentially the same as using two 1940’s vintage teletypewriters to communicate. It’s unchanged since the 40’s except with the substitution of computers for teletypewriters. This mode is susceptible to interference causing garbled text at times.

Packet - This mode uses an adaptation of protocols used on the internet where a packet of information is sent, then the receiving station sends back an acknowledgement if it was received correctly. No acknowledgement is sent if it wasn’t received perfectly without errors. This works well if the communication channel is clean and free of interference. However if the is natural or man-made interference, it may be almost impossible to get any of the long packets through without at least one error, so no data will be transferred since the whole packet has to be error free before any more can be sent. It CAN work well on HF if you have a strong signal and no interfering stations. This mode can also be used for sending text or binary files.

PACTOR – This is a mode that’s a combination of Packet and an older one called AMTOR. It has characteristic that make it much better on HF than Packet. It is a popular method used by Marine Ham Operators to pick up email from their boats. It cal also be used to send files.

PSK31 – This is a keyboard to keyboard mode that uses the computing power of the computer to create and decode a signal that can communicate even when you can barely hear it over the noise. It sends text at about typing speed. The basic mode has no error correction but it still perfume very well. If necessary a mode can be enabled that includes FEC (Forward Error Correction) which is much more robust. Throughput slows down when this is done.

Pictures

Many of the digital modes can be used to send digital picture files but that will take a long time due to the sizes of the files. Using the analog SSTV modes can greatly reduce the time to send a picture on HF down to less than a minute, at the price of maybe having interference in the picture.

SSTV – Slow Scan TV. This was not a digital mode when it was originally developed in the late 1950’s. However now computers are used to send and receive the images.

Any of these digital and picture modes are easy to use now with just a simple interface, either homebuilt or purchased, between your computer and a regular HF CW/SSB transceiver. Most of the time, the software is free. The ones I mentioned above and others don’t require a very speedy computer. Many older computers are way more than good enough. There are quite s few more of the digital modes, I just mentioned a few here. More are listed at sites like:

http://wb8nut.com/digital/

http://www.athensarc.org/digital-modes.asp

http://www.ogdenarc.org/downloads/HF%20Digital%20Mode%20Primer.pdf

http://www.dxzone.com/catalog/Software/SSTV/

I’ve just listed a few that I think are applicable here, probably PSK31 and SSTV will be easily used by beginners. I’m happy to answer any questions that someone might have.

August Johnson

KG7BZ