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[Music] Oh youtubers and fellow hams well in the livestream that we did a few days ago there was interest expressed in me doing a video on slow scan television and as you saw from the opening title there that's what we're doing today so slow scan TV is exactly what it sounds like it's slow scan meaning that they're scanning it down really slow a normal analog television signal would scan really fast drawing 60 fields per second in those fields being interlaced meaning that one field another field would like that and they would draw one field and then draw the other field making a full frame every twenty nine point something 29.97 or something like that frame a few frames per second close to thirty you know you could say thirty frames per second rounded up but it's actually a little bit less and that's regular television tell a meaning audio of course because you've got audio and video slow scan TV and they could leave the tella off and just call it slow scan be because there's no audio subcarrier it's just sending images and slow scan TV is kind of an extension of facsimile or fax if you really want to think about it the two modes share a lot of the same DNA and that they're using audio tones to transmit an image early fax machines used rotating drums a piece of paper would be affixed around the drum with the image to be sent and on the receiving side special paper that could be marked by an electric current would be affixed around the roller the rotation of the two drums would be synchronized between the two machines so they were rotating at exactly the same speed and then on the scanning side or the sending side a photo sensitive piece of electronics would sense whether the paper got dark or light as the drum rotated and an audio tone would be produced the intensity of the tone indicating how dark the sensed line was on this receiving side then the audio tone would be reversed back to Mark's on the paper by burning the paper and the more intense the audio tone was the darker the burn would be and that was how facsimile sent images using audio tones somewhere in the 1940s or 50s somebody figured out that the long persistent CRTs that were used in radar screens where the the image that's drawn on the screen fades out slowly that those screens could be used to do the same thing drawing an image from the top down line by line just like a fax machine on a rotating drum except that the image would then be drawn to a CRT and slow scan TV was born in this example to the lower right you can see where a slow scan TV image is being drawn on a long persistent phosphor CRT like would be used for radar and you can see how the image is faded out towards the top as the phosphor degrades but the persistence was long enough that you could see the image and this was exactly what early slow scan TV experiments were so as you can see early facili experiments led to transmission of still video images by ham radio operators across the airwaves and slow scan TV was born now as with the early fax machines the sending and receiving units have to be in sync with each other they have to be starting and ending each line at exactly the same time if they don't then the receiving unit will start drawing the lines may be a tiny bit early or a tiny bit late and each progressive line will shift end up with a slant to the resulting image most slow scan TV will software will have a slant control that allows you to correct for that on the receiving end as you're receiving the images and indeed a lot of software does it automatically most slow scan TV modes will have a sync pulse at the beginning of each line it Nick that you'll hear at the beginning of each line and the software can use that then to make sure that the lines are in sync and drawn to create a straight image now early slow scan TV modes were all black and white as you could see there they used green screen phosphor CRTs so there was no color as an option and the intensity of the line was varying via the audio tone but no color information so it was simply a black and white image as computers came into being with slow scan TV and more control and functionality was possible they figured out ways of doing color images and the way that they would do a color image is they would simply do three tone sweeps per line really quick one for red one for green one for blue or if they wanted to use the other color model one for yellow one for magenta one for cyan and then maybe one for black perhaps if they really wanted to mix it I don't know there's so many different modes that have been developed now for slow scan TV dozens of them if you look at a webpage in the list of modes it's just an extensive list everybody's come up with new ways of doing it and different ways of moving the image across but primarily they all use a sweeping audio tone as you're scanning across the line to denote the intensity there is one stand out though developed for the amiga computer back in the late 80s Early 90s and it's a mode called a TV which amiga television I don't know exactly what it stands for but it was designed on the Amiga computers and it used a more organized digital chunk method of sending data so you ended up with a good image every time without any of the timing issues or slant they were basically encoding the digital data of the image and sending that across so trellis coding or something it's similar to the way modems were used to send digital information across phone lines except they did it across the across the airwaves so that's the only mode that's different in methodology but the rest of the slow scan modes still pretty much work the same so what about software to allow you to experiment with slow scan TV well there's free software out there I'm going to talk about two packages real quick on the windows side of things there's a program called MMS STV it's freely available and the link will be down in the description it does most of the slow scan TV modes for Windows just fine lets you compose images as far as adding text within the program and transmit and receive and maintain a gallery of images under linux a free program that's available is called qss TV and again it does all the different slow scan modes just fine allows you to do some basic image composition stuff but it also does a DRM digital radio mondale images which is a newer heavily digital format and a hybrid of that that allows you to use the internet to ftp the images after establishing the connection over the radio but that's a subject for a whole different video as far as slow scan TV though it works just fine I'm not a hundred percent certain at the time of recording this but I think for the Mac there might be a version of qss TV cross-compiled if not I'm certain that there are some free slow scan TV apps for the Mac out there perhaps somebody will leave one in the comments below and I will pin it to the top for those of you looking for software so that's slow scan TV in a nutshell it's pretty neat I sometimes enjoy just leaving the software running on one of the common frequencies there is a website that lists all the common frequencies up with that in the description below as well but the two most often used are going to be on 20 meters and 40 meters and on 20 meters you'll usually find slow scan analog on 14 to 30 and the DRM stuff tends to show up on 14.2 33 40 meters sometimes you'll hear slow scan TV on 7.1 71 is that right yeah I think that's right yeah 71 71 is where you'll find slow scan TV on 40 meters usually in the evenings but 20 meters is by far the most busy if you can tune to 14 to 30 most days and find some slow scan TV activity so get on there play around with it you can use any digital interface like you would use with any other digital mode ready ft 8 whatever signal links my own do we know Vox rigged blaster any of those will work just fine it's a regular audio mode get on there play around with it have fun with it it's kind of neat being able to send images across the air even though it's kind of old hat these days it's still kind of neat I'll close this video out with a live demonstration we'll point the camera at the radio and find somebody sending an image and let you let you watch that build in real time [Applause] [Music] [Music] you thanks for watching if you enjoyed the video don't forget to give it a thumbs up also if you're not already a subscriber click to subscribe join us on the Facebook channel for discussion about the videos and if you'd like to help support this channel please click to support me on my patreon page