The following document is an extract from the MMSSTV group on Groups.io and it’s an extract from a question by Daniel KD4VBV and an answer from Stephen WA8LMF. Duncan VK2DLR has edited its brevity without changing the content. (Removed lots of time stamps, headers, email and home page details as well as combining two answer from WA8LMF). The discussion reflects the opinions of the authors of the post and is presented as such. It does contain much fascinating information on the analogue SSTV mode, The most common program used for SSTV is MMSST by Makoto Mori. The most significant modern update to the classic MMSSTV software is YONIQ (MMSSTV-YONIQ), developed by EA1ADA and available via HamSoft.
Extract from MMSSTV Groups.io post 10FEB2026.
Question from Daniel KD4VBV: What is the preferred size for images to be sent over SSTV and is bitmap the standard format?
Reply from Stephen WA8LMF:
The vast majority of SSTV transmissions use the 320×240 pixel “half VGA” format originated over 50 years ago. These modes trade off various combinations of noise immunity, image quality, and transmission time. On HF, where noise and multi-path propagation can degrade images, the longer-transmission-time modes are preferred. (Unless one has an exceptionally strong signal.) On VHF-FM, where one normally has a noiseless path, the faster (shorter-transmission-time) modes will work well. Only a handful of modes generate 640×480 “full VGA resolution or 800×600 “SVGA” resolution. These modes, mostly in the PD-xxx family, take much longer to transmit. The shortest color mode is “Robot 36” which takes, as it’s name suggests, 36 seconds for a 320×240 frame.
For the shortest possible transmission time, use the “great grandaddy” of all SSTV formats, originated in 1959, the 8-second 120-line black-and-white (actually grey scale) mode. This is usually labeled “BW8”: A slightly-longer variation is the BW12 format. This is still used today for simple CQ slides with very limited text, since it can blast out a complete transmission in less than 10 seconds. It is a complete waste of air time to transmit simple CQs in the 90-second “Scottie 1” mode as so many people tend to do. If you MUST have color for CQs, at least use the 36-second Robot 36 mode instead.
SSTV programs can & will automatically downsize higher-resolution images to fit the 240, 480 or 600-line formats of the SSTV mode being used. However, since even the best SSTV images have a fraction of the detail (resolution) of even a cheap cellphone-cam image, it is important to keep the original image as simple and uncluttered as possible. Crop aggressively so the main subject will fill as much of the frame as possible.
Don’t use thin spindly or decorative fonts for text. — use simple bold fonts with thick strokes at larger point sizes to remain readable through noise and interference. And finally, a major issue today since so many images are produced on cell phone cams: -ALL- SSTV formats use the 4:3 aspect ratio (width to height ratio) of classic 35mm film and analog broadcast TV that existed when SSTV was born in the early 1960s. Today, many images taken by digital cameras and cell phones are in the 16×9 wide-screen format of digital broadcast TV. It you allow the SSTV application to “squish” this shape image to fit the 4:3 format of SSTV, the picture will be oddly distorted. You must crop out a 4:3 portion of the original image for SSTV. (MMsstv has a 4:3 box that can be dragged out over the original image, to choose a properly-portioned part of the original image for transmission.)
SSTV, as practised today (and for the past 45-50 years) is NOT a digital mode. It’s actually analog. It transmits scanning lines – not digital pixels. It’s literally classic analog NTSC TV, as done in North America before before the 2009 switch to digital HD TV, in slow motion. NTSC broadcast TV transmitted 15,000-odd scanning lines and 60 frames per second. SSTV slowed that down to about 15 lines/sec and a single frame over 8 seconds. This reduced the data rate enough to fit into a single 2.5 KHz SSB bandwidth voice channel, instead of a 6-mHz-wide VHF or UHF TV channel, for the original classic 8-second B&W SSTV mode.
A slightly faster version of this transmitted 10 low-resolution frames/second live from the moon during the first moon landing in July 1969.
In today’s SSTV operation, the over-the-air transmission is still analog. It only becomes digitized into pixels at the receiving end for display on computer screens. There is a so-called SSTV mode that IS truly digital — the orphaned program “EasyPal”. EasyPal could send any kind of computer file (not just pictures) over-the-air error-free using two-way ACK/NAK handshaking between the stations involved. It was gaining popularity until it’s Australian author died abruptly in 2014. Activity on this mode is now nearly non-existent. It used multiple parallel audio QAM audio subcarirers in an SSB bandwidth, in a mode similar to the “56K” dial-up modems used on land-line phone lines in the ’90s and early 2000s. Because it used as many as 64 simultaneous audio tones in the voice band, it was very finicky about audio level settings, distortion in the TX and RX audio paths, and required wide and flat audio response in the radios. But it did work. I actually sent “LiveCAM” shots of western scenery from my car with it in the late ‘2000s on cross-country road trips.
The new “gold standard” for error-free transmission over ham radio is the soundcard “soft-modem” application called “VARA”. VARA can achieve 22,00 baud transmission error-free on FM, 1500 baud transmission (faster than 1200 baud 2M packet) in a 500 Hz CW bandwidth on HF, and over 10,000 baud in a 2.5 KHz SSB bandwidth on HF under good band conditions. It transmits data wrapped in two layers of forward error correction; i.e. it almost always can fixed a file damaged by noise at the receiving end without re-sending it. If FEC can’t fix the file by itself, a two-way handshaking arrangement between the two stations will automatically resend the bad blocks (not the entire file).
VarAC Chat is a sophisticated terminal program that runs “on top of” VARA. It is intended for live keyboard-to-keyboard live chat, but can also do email and file-transfers. If the file being transferred just happens to be a JPG or BMP, you essentially have a fully-digital replacement for SSTV. You in VE-land have no issues doing this. We in the US do. Our creaking wheezing communications regulators arbitrarily divided the HF ham bands between voice and non-voice modes generations ago. For some perverse reason, in the early 1960s, they decided “image” transmission (i.e. SSTV”) should be allowed in the voice band segments only, while “data” (packet, RTTY, etc) should be allowed only in the non-voice band segments, apparently viewed as an outgrowth of CW.
Today, we are in an era where ABSOLUTELY EVERYTHING is digitized for transmission (even analog land-line phone calls), and “5G” cellular now uses Internet Protocol transmission even for voice calls. Our FCC (Federal Communications Commission) STILL continues to tie itself in knots trying to distinguish between “image” and “data” transmission. If the digital “bag of byes” I transmit over ham radio represents a picture, it is supposed to be in the voice bands. If I send a “bag of bytes” that represents a text file (email) or a Word document instead, WITH THE IDENTICAL PROGRAM, it is supposed to be in the non-voice CW band segments. [Decades ago, during the early rise of land-line data modems, the FCC actually tried hopelessly to distinguish between”information” and “data” in regulating non-voice traffic on phone lines – really!]