Sending Pictures Via Radio
Exchange Pictures Wordwide Using Amateur Radio
The first steps to transmit pictures used wire to connect transmitter and receiver. As might be expected, initially the transmissions were of single pictures and it was much later that transmissions were of multiple photographs to the stage where we have television.
Now and the Amateur
While sending pictures by amateur radio might seem to be a very expensive and complicated process, the advent of computer based signal processing techniques and relatively simple and inexpensive equipment has made this part of the hobby much simpler than it might appear. There are a number of groups involved in experimentation and operation in this aspect of amateur radio and those interested should find someone in their local club who can provide steerage towards a successful knowledge of what and how.
Sending Single Photo’s – Facsimile and Slow Scan TV (SSTV)
A "fax machine" usually consists of a means of scanning the image, a device to convert that scanned image into an encoded signal that can be transmitted ( the modem) a means of transmitting the signal and , at the other end, some form of receiver, decoderand printer to reproduce the image.. The first patent for such a device using wire as the transmission means was issued in the 1840’s but it was not until the 1920’s that radio was successfully used to transmit facsimile images.. Weather information images are a common usage of radio fax today. Facsimile for the amateur involves scanning the image and encoding that information.. That encoding is transmitted in the form of audio tones which are within the usual voice frequencies and hence can be readily transmitted with either Frequency Modulation (FM) in VHF or UHF bands or Single Sideband for HF bands.
There are similarities between Fax and Slow Scan TV in that to transmitting a photograph or map is often spread over several minutes using coded low frequency tones and this process produces a signal that can be readily transmitted by HF radio.as well as by VHF or UHF.. Both Facsimile and SSTV can transmit signals in colour, usually by the use of multiple scanning of each line using the three primary colours of Red, Green and Blue.
The majority of amateur stations operating in Fax or SSTV modes use the power of the computer to generate the required tones and to to decode them back to pictures which can be displayed on the computer screen or printed.
There are a number of software programs allowing the amateur to operate in the Fax/SSTV modes.