Slow Scan Television is a picture transmission mode developed and used by the Amateur community for quite some time. The original SSTV required expensive commercial equipment. Today, with Personal Computers, Software and a Interface to your transceiver you can be on the air with SSTV.

While SSTV signals are FAX-like in function they do not possess the scratching quality of the FAX signal. The sound of an SSTV signal is more tonal in its composition. It is considered that each mode cannot be distinguished apart by ear. SSTV unlike domestic television is a method of transmitting still pictures over a very narrow bandwidth, on frequencies normally used for speech by Radio Amateurs.

SSTV was originally invented by Copthorne Macdonald and first used by Radio  Amateurs. The original idea was to find a method of transmitting a television picture over a single speech channel. This meant that a typical (at that time) 3MHz wide television picture had to be reduced to around 3kHz (1000:1 reduction). Slow Scan Television occupies the same amount of bandwidth as a typical SSB signal. The choice of time base for synchronising was the readily available domestic power supply at 50 or 60 Hz (depending on the country of origin). This gave a line speed of 16.6Hz and 120 or 128 lines per frame (against the then UK standard of 405 lines (now 625) per frame), giving a new picture frame every 7.2 or 8 seconds.

The hardware used to receive/transmit SSTV is a sound card or you can build/buy an interface which uses one of your serial ports of your computer. The shareware software can be freely downloaded from the internet. There are also programs available for different operating systems. 

An Amateur Radio SSTV transmission is transformed to an audio signal. Each colour has its own tone between 1500Hz (BLACK) and 2300Hz (WHITE). A SSTV picture has 256 lines with each line  transmitted 3 times (the 3 RGB colours). There is a compromise between image quality and time. At one extreme we have low resolution (120 line) black and white images which take only 8 seconds. At the other end we have software providing high resolution with 16 million colours at 640 x 480 resolution which take up to 7 minutes. Most images these days are full colour 320 x 240 resolution. The average time taken to send  a HF SSTV picture varies although 2 minute period  could be considered average using Scottie S1 for example.

In other words, the signal frequency shifts up or down to designate brighter or darker pixels, respectively. Colour is achieved by sending the brightness of each colour component (usually red, green and blue) separately. This signal can be fed into an SSB transmitter, which in part modulates the carrier wave.

There are a number of different modes of transmission, but the most common ones are Martin M1 (popular in Europe) and Scottie S1 (used mostly in the USA). Using one of these, an image transfer takes 114 (M1) or 110 (S1) seconds. Some black and white modes take only 8 seconds to transfer an image.
 

A transmission consists of horizontal lines, scanned from left to right. The RGB colour components are sent separately one line after another in the order R, G, B. Some Robot modes use a YC color model, which consists of luminance (Y) and chrominance (R-Y and B-Y). The modulating frequency changes between 1500 and 2300 Hz, corresponding to the intensity (brightness) of the color component. The modulation is analogue, so there is not a defined number of pixels in each line; they can be sampled using any rate (though in practice, the image aspect ratio is conventionally 4:3). Lines end in a 1200 Hz horizontal synchronization pulse of 5 milliseconds (after all colour components of the line have been sent).

With the introduction of Robot 1200C, Robot Research introduced the VIS code, which is used to indicate the speed and mode at the beginning of the transmission. The VIS code, when decoded by the receiving station, will let the receiver automatically set the necessary parameters for proper reception. The VIS code is sent as part of the vertical sync pulse and is 10 bits long lasting 10*30ms. The start and stop bits are represented as a 1200Hz tone with the remaining 8 bits (including 1 even parity bit) left for encoding information. This breaks down as 1 30ms start bit at 1200Hz, 7 data bits, each 30ms, sent Lowest Significant Byte (LSB) first (logical '1' is transmitted as 1100Hz, logical '0' is transmitted as 1300Hz). 1 30ms even parity bit and 1 30ms stop bit as 1200Hz.

Below is a table of some of the most common SSTV modes and their differences. These modes share many properties, such as synchronization and/or frequencies and grey/colour level correspondence. Their main difference is the image quality, which is proportional to the time taken to transfer the image and in the case of the AVT modes, related to synchronous data transmission methods and noise resistance conferred by the use of interlace.

SSTV Standards for Synchronization

Parameter	Value
Synch Tone	1200 Hz
Black Tone	1500 Hz
White Tone	2300 Hz
Picture Synch	30 ms
Line Synch	5 ms

SSTV Modes

Mode		Type	Time [s]	Resolution[Pixel x Line]	Notes
Martin	M1	RGB	114	320 x 256	a
	M2	RGB	58	160 x 256	a
	M3	RGB	57	320 x 128	b
	M4	RGB	29	160 x 128	b
Scottie	S1	RGB	110	320 x 256
	S2	RGB	71	320 x 128
	S3	RGB	55	320 x 128
	S4	RGB	36	160 x 128
	DX	RGB	269	320 x 256	*
Robot	8	B/W	8	160 x 120	c
	12	B/W	12	320 x 120
	24	B/W	24	320 x 240
	36	B/W	36	320 x 240
	12	YUV	12	160 x 120	*
	24	YUV	24	320 x 120	*
	36	YUV	36	320 x 240	*
	72	YUV	72	320 x 240	*
B/W Mode	SC-1 8	B/W	8	128 x 128
	SC-1 16	B/W	16	256 x 128
	SC-1 32	B/W	32	256 x 256
Wraase	SC-1 24	RGB	24	128 x 128	b
	SC-1 48	RGB	48	256 x 128	a
	SC-1 96	RGB	96	256 x 256	a
	SC-2 30	RGB	30	256 x 128
	SC-2 60	RGB	60	256 x 256
	SC-2 120	RGB	120	512 x 256
	SC-2 180	RGB	180	512 x 256
Scanmate	1	ROB	391	310 x 512	*
	2	RGB	261	310 x 512	*
	DX	RGB	269	256 x 256	*
AVT	24	RGB	24	128 x 128	*, d
	90	RGB	90	320 x 240	*, d
	94	RGB	94	320 x 200	*, d
	188	RGB	188	400 x 320	*, d

 

Mode Name	VIS Code	Picture Size	Pixel Time (exact)	Total Picture Time (exact)
PD240	97*	640 x 480	382 microseconds	248.00000 seconds
PD180	96	640 x 480	286 microseconds	187.05152 seconds
PD120	95	640 x 480	190 microseconds	126.10304 seconds
PD160	98*	512 x 384	382 microseconds	160.88320 seconds
PD90	99	320 x 240	532 microseconds	89.98912 seconds
PD50	93*	320 x 240	286 microseconds	49.68448 seconds
PD290	94*	800 x 600	286 microseconds	288.68224 seconds

 

Notes:

*        Not implemented

a        Top 16 lines gray scale

b        Top 8 lines gray scale

c        Similar to original SSTV

d        No Horizontal Sync (start of a new line)

SSTV - Experimental modes

Mode	Time (sec)	Pixel resolution	Comments
MP73	73	320x256	Colour differentiation
MP115	115	320x256	Colour differentiation (in use)
MP140	140	320x256	Colour differentiation
MP175	175	320x256	Colour differentiation
MR73	73	320x256	Colour differentiation
MR90	90	320x256	Colour differentiation
MR115	115	320x256	Colour differentiation
MR140	140	320x256	Colour differentiation
MR175	175	320x256	Colour differentiation
ML180	180	640x496	Colour differentiation
ML240	240	640x496	Colour differentiation
ML280	280	640x496	Colour differentiation
ML320	320	640x496	Colour differentiation

MP mode is based on the colour difference scheme that the PD mode uses.
This mode should be useful for reducing multi-path distortion and jitter.
The scan time for each pixel is longer than the other modes, but the
colour information along the vertical axis is compressed.

MR/ML mode is based on the colour difference scheme that the Robot 24/72 mode uses. This mode is aimed for offering good resolution in good conditions. The colour information along the horizontal axis is compressed.

These modes are not new to SSTV and are a compromise between the transmission time, picture size, and quality. These modes are in the experimental phase and are subject to alteration.
 

SSTV transmissions can be seen on the following frequencies: (List is not conclusive or official)

Band	Frequency	Sideband
80 meters	3.630 MHz kHz (AU) 3730 (Europe)	LSB
40 meters	7.033 MHz (International call )	LSB
30 meters	10.132 MHz (Region II) 10.144 (Region I) MP73-N mode - 10.132 (Region III)	USB
20 meters	14.230 MHz (International call ) 14.227, (14.236 MHz VK5ZW S&F SSTV repeater)	USB
15 meters	21.340 MHz (International call )	USB
10 meters	28.700 MHz (VK8NSB SSTV analogue store and forward repeater.)	USB
10 meters	28.680 MHz (International call )	USB

1. 640 x 480 image has 4 times the resolution of a 320 x 240 picture and will require four times as much time to transmit. 

2. Colour images require from 2-3 times the time required for a gray scale image of the same resolution. 

3. The rate for transmission if the pixels in an image line cannot go much above 2000 pixels/second without exceeding the bandwidth permitted for SSTV operation. 

4. Some SSTV modes make take excessive time to complete and time out a repeater. (primarily UHF/VHF).

5. Slow Scan Analogue builds a picture "line by line" whereas the digital mode is decoded "block by block" which requires a much faster computer of at least 1Ghz, as decoding time depends on the speed of the CPU and RAM.
Digital (DSSTV) transmitted pictures do not require slant adjustment which is often necessary with analogue transmissions. SSTV slant adjustment help.

6. The standard mode used by European stations is MARTIN1. USA and JAPAN and Australia mainly use SCOTTIE1 as the standard. All other modes are not often used, only for short experiments! which were developed by Volker Wraase in Kiel, Germany. Martin was developed by Martin H. Emmerson, G3OQD/England. Scottie was developed by E.T.J. Murpy, GM3SBC/Scotland. Robot was developed by Robot Research.
 

In the SSTV mode, a report is given in the RSV form.

R = RADIO (from 1 to 5, 5 is the best)
S = SIGNAL STRENGTH (1 to 9)
V = VIDEO (from 1 to 5, 5 is the best)

Therefore when a good picture is received with signal strength of 9 a RSV 595 is given.

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Approximate guide to frequency bands and ranges   Approximate distance Day Night Less than 300 km 3–4 MHz 2–4 MHz Between 300 km and 750 km 4–6 MHz 3–7 MHz Between 750 km and 1,500 km 5–9 MHz 6–10 MHz Between 1,500 km and 2,500 km 8–12 MHz 7–11 MHz Between 2,500 km and 5,000 km 10–18 MHz 8–15 MHz   Band (meter) MHz Use* HF 160 1.8 - 2.0 night 80 3.5 - 4.0 night and local day 40 7.0 - 7.3 night and local day 30 10.1 - 10.15 CW and digital 20 14.0 - 14.350 world wide day and night 17 18.068 - 18.168 world wide day and night 15 21.0 - 21.450 primarily a daytime band 12 24.890 - 24.990 primarily a daytime band 10 28.0 - 29.70 daytime during sunspot highs VHF 6 50 - 54 local to world-wide 2 144 - 148 local and medium distance UHF 70 cm 430 - 440 local * It should be noted that band conditions vary for many reasons and thus all of these bands can at times take on the characteristics of others. See the section on Propagation. This table should be considered a general guideline. (http://www.eham.net)

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Store and forward is a communications technique in which data is sent to an intermediate station where it is kept and sent subsequently to the final destination or to another intermediate station.

VK5ZW uses a single frequency of 14.236 MHz USB. An access tone of 1750 Hz is required for activation.
Operating hours are between 19:30 and 12:30 UTC 7 days a week. 

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It is recommended that you have both FSKID Encode and Decode enabled on your software. EncodeE FSKID - This will send a FSK signal with your call sign at the end of the image which can be seen in the call window on the receiving station and emplaced in template Macro commands.

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Website designed and maintained by Trevor VK2QW Last updated 05/01/13