11 SPECIALIZED COMMUNICATIONS

AMTOR/ PacTOR/ CLOVER/ G-TOR/ PSK31

Besides Packet and RTTY, digital modes which have been used among hams include AMTOR, PacTOR, CLOVER, G-TOR, and PSK31. This manual does not describe much about these modes. For details, consult reference books about Amateur Radio.

AMTOR (AMateur Teleprinting Over Radio) has brought amateur HF digital communication into the computer age. It is the first error-free HF digital mode by which data bursts (not steady stream of data) are transmitted.

PacTOR (Packet Teleprinting On Radio) has combined the best features of both AMTOR and Packet to improve the efficiency of HF digital communications. Like Packet and AMTOR, PacTOR sends error-free data using a handshaking method.

Of all the Amateur Radio HF digital modes, CLOVER offers the best overall performance using a complicated modulation technique, automatic power adjustment and other advanced features. It may allow communications to be maintained under the worst conditions.

G-TOR (Golay-coded Teleprinting Over Radio) is a relatively new Amateur Radio digital mode currently in use. G-TOR was developed specifically to handle the adverse conditions of communicating, across the solar system, with spacecraft during their missions.

PSK31 was developed by an RTTY enthusiast, G3PLX, in the Great Britain. The operating technique is very similar to the conventional Baudot-RTTY, although more sensitive fine-tuning is required, as a PSK31 signal requires a tuning accuracy of a few Hertz. A special feature of PSK31 is that it allows the entire ASCII character set, including the back space character.

Your MCP should handle some or all of the above modes. For available modes on your MCP, consult the instruction manual for the MCP. For the cable connections, see “MCP AND TNC” {page 95}.

On most HF bands, audio frequency shift keying (AFSK) is used for the above modes. This method of modulation uses audio tones therefore either LSB or USB mode should be selected. Traditionally, LSB is used, similar to RTTY, with the exception of AMTOR which is normally operated in USB.

AMTOR activity can be found on or near 14075 and 3637.5 kHz. These are also good starting places when searching for PacTOR, CLOVER, G-TOR, or PSK31 stations.

Note: When using SSB mode for digital operation, use a fast AGC setting and switch your Speech Processor OFF.

SLOW SCAN TV/ FACSIMILE

Slow-scan Television (SSTV) is a popular application for transmitting still images over the air, from one station to another. Instead of trying to describe your station, simply showing it is much faster. Transmitting images over the air requires a scan converter, besides a transceiver. A scan converter transforms images taken with a video camera into audio signals that can be fed into your transceiver. The recipient’s scan converter transforms audio signals back into video images so that he or she can view them on a TV set.

Nowadays instead of a scan converter, many hams use a personal computer, a software application, and an interface attached to the transceiver. This is much cheaper, more flexible, and does not require a TV set. In recent years, many low cost digital cameras have become available. You can transfer images from these cameras into your computer.

For further information, consult reference books about Amateur Radio. The frequencies (measured in kHz) commonly used for SSTV operation are listed below:

U.S.A./ Canada

ARU Region 1

(Europe/ Africa)

 

3845, 3857

3730

~ 3740

 

 

 

7171

7035

~ 7045

 

 

 

14230, 14233

14225

~ 14235

 

 

 

21340

21335

~ 21345

 

 

 

28680

28675

~ 28685

 

 

 

145500

 

—

 

 

 

Fax (facsimile) is one of the original image transmission modes. Using this mode allows you to exchange more detailed graphics than SSTV. Amateur Radio fax functions much like old analog fax systems. It scans paper and converts acquired image data into a series of tones representing white and black portions of the image. Because fax requires longer transmission time, you should use it only when band conditions are stable with strong signals.

Popular fax frequencies include the following:

•7245, 14245, 21345 (International Net), and 28945 kHz

Operating on SSTV or fax mainly involves learning the functionality of your computer application or accessory hardware that supports these modes. Consult the instruction manual that comes with your software or accessory equipment.

Note: When operating either SSTV or fax, use a fast AGC setting and switch OFF your Speech Processor, for best results.

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