 Hi, my name is John Marlar, call sign Kilo 4 Charlie Hotel November K4chan. Today I'll be giving you a presentation that's an introduction to the common digital modes used by amateur radio operators. But before we get into that I'm going to introduce myself. My first ham radio was given to me by my grandfather. It was a Lafayette KT200. Still have it, recently rebuilt it. I now know that it's called a boat anchor and I know why. I first took the technician test at DEF CON 27, passed it on my first try, took the attempt of the general right after, did not pass the general, studied hard, came back the next year and passed my general. I spend a lot of time on voice modes on 40 meters but I am fairly active on 40 meters on FT8 and I'll talk more about what FT8 is later when I talk about the data modes. It's one of the digital modes we'll talk about today. I also have been known to do a lot of lurking on 14-230 for SSTV images and I'll talk a little bit more about this but this is something that's really easy to do, even if you don't have an amateur radio license. One of my hobbies is fixing a lot of things. I know this is information security conference and people like to talk about all the letters behind their names and all the stuff they do in Infosec. One of my big hobbies is fixing electronics and building electronics and a lot of times when I fix things I have to break them more first. With that introduction out of the way, let me talk about the agenda for today. First I'm going to give you a brief introduction to some of the common voice digital modes that are available and we'll talk about some of the commercial and the open source digital voice modes and then we'll get into the digital data modes. This is where a lot of people are very active and there's a lot of different things you can do in terms of data for the digital modes. Throughout this presentation I'll be talking about various forms of hardware that is both commercial and open source or DIY and I'll even show you a very simple kind of basic DIY solution that I came up with for how to easily enable push-to-talk control on a physical radio from a Raspberry Pi in a way that makes it easy to connect to different radios. I'll be talking about that. Finally I'll conclude with a pre-recorded demo of an SSTV QSO that I do with my father-in-law. Let's start by talking about digital voice. Really before we get too deep into this, let's talk a little bit about what a digital voice signal is. We all know as radio operators what a radio signal is. You take a carrier wave, you have an input signal and you apply those two and you get a modulated signal. Really the difference kind of at a very high level between analog and digital is that the input signal that you're applying on that carrier wave is a encoded digital voice signal rather than an analog voice signal and that's really kind of like at a 10,000 foot level the difference. Once you get beyond that and you start to go deeper into the layers of how that actually works, one of the things you have to think about with digital voice is how do you define a channel and how do you deal with multiple people or multiple transmission sources all speaking in the same frequency range or in the same section of bandwidth if you will and how do you divide that bandwidth up. There's a bunch of different methodologies for that. Two of the more popular ones are FDMA and TDMA and one divides up that bandwidth by the frequency and one divides it up by the time, so time division or frequency division. Those are two of the more popular ones and you can actually combine the two. You can do FDMA and TDMA at the same time so you can divide into instead of say two channels or four channels you can have 16 channels and every time you divide it up into smaller pieces depending on the mode that you're using that may limit the bandwidth that you have and it may change how that works. I won't get too deep into the theory here but I wanted to give you just a little brief introduction in that. If you're really interested in the theory there's a lot of interesting stuff you can read on Wikipedia and other websites. So when you get right down to it what are some of the ways that you can, what are some of the implementations of digital voice? Really most of the systems use what's called AMBE or AMBE plus two as their voice encoder and the voice encoder is kind of the first step to digital voice communications and what a voice encoder does is it takes your an analog voice signal and it digitizes it. So the AMBE system which is the most popular is also a little bit controversial because it is patented and it's still protected by a patent and it requires a license from a company called Digital Voice Systems Incorporated. Usually the way that this is achieved by the the commercial manufacturers the little chips that you see there on the screen in the bottom right corner those are DVSI voice encoder chips and they include that license so when you buy the chip you also get a license which basically means digital voice systems gets a little piece of it. This is a slight bit controversial because of the in the US the FCC rule that says any transmission is must not use proprietary technology and while the the spec is basically open it's encumbered by a patent and it requires paying the patent owner for a license. So it as a response to this there are a couple of open source implementations of digital voice there's a free DV and M17 or two of the more popular ones that and these use a voice encoder that's not encumbered by patents but the commercial solutions like we have up here the DSTAR the YASU system fusion also their WiresX and DMR digital mobile radio and also P25 these all use that that AMBE system that requires that that commercial chip and when you buy a radio it's not something you really have to worry about but it is something that you should at least know and really the most important thing here is that for the most part you need to have a system that is compatible when you're it is compatible with the other person you want to speak to so if you want to speak to someone who has a DSTAR radio and they're transmitting a DSTAR and they can receive DSTAR you need to have a system that's DSTAR compatible and that's kind of really the the most important thing to understand here is that most of these protocols aren't compatible with each other you can't talk to a DMR radio with a a YASU system fusion compatible digital radio because those they're they're different they use different technology the technology is basically different without getting too far into the weeds on that so that's really the important thing to understand if there's say there's a lot of of groups ham groups around the world that that kind of choose a platform whether it be M17 or YASU system fusion and you know and they all kind of you know they they all work with that same system and if you're interested in getting involved with those groups you need to make sure that the hardware you buy is compatible with that so just something to know YASU system fusion also referred to as YASF a lot of times you'll see as you know as a ham operator there's a million abbreviations that you need to know so YASF is what people use for YASU system fusion which YASF is different from wires X and without getting too deep into the the weeds on that why wires X is a system that is connected to the internet and you can also connect to from a radio and that gets repeated on to the internet and i'll talk more about that when I talk about hotspots but that's a difference that's a different style of system and it requires a different connection method than just a say a repeater that uses YASF digital modes so one of the questions um you know it is people often ask is well why would I want to use a digital voice mode I can use an analog voice mode and I can talk to any radio on the planet why would I want to use a proprietary digital voice mode and really the the reason is you get a much you're more likely to have a good connection with a weaker signal so the the graph that I've got here in the screen kind of shows how that that arc looks and if you compare the analog signal you can see where that starts to drop off the voice quality starts to drop off and it has a rather steady decline out pretty far to where where you're not going to have very good quality and you're going to have a hard time making good making qso's and making contacts and having people understand you whereas with the digital modes there are a lot there are a lot better at making a good connection with even a weak signal but then they fall off a cliff really fast so once that signal gets to a certain level of weakness depending on the mode that falls off a cliff pretty fast and it just it just basically stops working it's very similar to if you ever use digital tv you really you get a really great crystal clear picture it just drops out almost entirely digital voice is almost the same way so that's one of the main reasons that people use digital voice also depending on the system that you're connecting to if you're connected to something like a wires x digital system there's all sorts of things that you can connect to like they have rooms and channels and all of these rooms and channels can also be connected over long distances by the internet so if you have say a local repeater that's on two meters that you can talk to that you can reach from your area and it's a wires x it's a wires x node and you can connect to it and then you can talk to hams that are on the other side of the world just using your you know relatively otherwise low powered radio that can that can talk to that wires x node you can join in the rooms they have lively discussions about different things and different topics so that can be really fun and it's a great way to meet people and talk to people so that's something that i if you have the the right kind of equipment i definitely recommend checking it out i have a yesu ft-991 and it's wires x compatible and when you get it to work it's it's pretty cool so i definitely recommend checking it out but um you know each of the different manufacturers have their own versions of that so let's say i've convinced you you're like this sounds great john i'm sold how do i get started in digital voice there's really you know two ways one is you buy a a radio that's compatible with digital voice like i said i have a yesu ft-991 it does the the yesu system fusion it does wires x it's you know but it's the the shack in the box if you will and it made it really easy for me to get started in digital modes because it just kind of does it right out of the box and wires x is a little bit of a challenge to get set up and find a node that works over the radio but once you get it set up and you get it working it's really cool i com has their own version of digital um the ic 7100 7300 i believe and also i have up there on the screen the id 52 which is a handheld digital radio might only be available in japan right now there's a chip shortage everything and i think they're having production problems right now so those are all and even i've got a i've got a pofong up there um they have a digital radio that is dmr compatible um so there's that as well one of the other ways is kind of more the diy route if you will and you can build what's what's called a hot spot um and the cool thing about a hot spot is you can you use something like a raspberry pi and you have a little a little radio that you connect to it and you can connect to the radio over a very low power um you know using just q r p bandwidth basically and then that digital hot spot will may will convert that into a digital signal over the internet and then it can connect to other digital hot spots and then that can be rebroadcast or um you can talk to hams online that are just completely online so um that's another way you can get started with that um people love the hot spots um the hot spots are a great way to um bridge between networks um so some of the hot spots you can connect to with your you with your yesu radio and then you can get onto a common network um so it it really depends there's a lot of stuff you can do with that and you can really if you like to tinker with the electronics um the the raspberry pi hats are a great way to do that and get started on that really um you know in the open spot is a is a great hot spot that's kind of a commercial version of a hot spot um and it does all the different digital modes and it's got its own battery built in it's a little expensive but if you're looking for something that's more uh that's less diy and and uh and more kind of not quite plug-and-play but as close to plug-and-play as you're going to get uh something like that the open spot's a great a great choice um and to talk about the ham radio village there's a lot of digital stuff that the ham radio village offers i'm not going to go through each one of these here but if you check out their their twitter page which is really easy it's at ham radio village on twitter they have a sticky post up there that talks about all of the hot spots that are available and all the digital modes and how to connect to all that so and this this information's up here they've got geisu system fusion not wires x but the ysf they've got that set up an m17 dmr d star in two different modes of d stars there's two different there's a few different modes so if you have a digital radio and you're going to be at the con and you're looking to connect that so definitely check that out and check out their twitter page or or just take a screenshot of this and and uh check it out so now that i've talked about uh the voice modes let's talk a little bit about data um and this is where it gets really interesting so the first data mode that i'm going to talk about is rtty and this is really kind of the first widely adopted digital mode i'm not going to say it's the first um i think it's the first but it's the first that was uh if it's not absolutely the first it's the first that gained a lot of a popular adoption um the speed for uh for rtty is about six characters per second so not very fast it uses a method of transmission called murry or botat code um and uh it's it's very slow so 45.5 bot there were some improvements that were made to it over the years so you can get up to 75 bot but with the limited character set that it has there's not a whole lot of messages that it it's very limited in what you can send this was used by the us navy and one of those pictures up there is actually a us navy a rtty station um back when radios could fill entire rooms uh and it took you know entire rooms to have very basic computers that's what it looked like and this uses frequency shift keying as its as its modulation method for for sending that um so one of the problems that that we have with rtty is it's very prone to interference and it has no error correction so that means the side that's receiving doesn't really know if there was an error in the transmission or something was missed it has no way to request a retry um when you monitor rtty the radios um uh you just get random characters you can just be listening to what sounds like static and you'll see random characters pop up so um i've tried to uh i've i've tried several times on rtty and and i haven't had a whole lot of luck but that may be due to the fact that i have a really uh i have a homemade antenna and it's probably not perfectly tuned and i don't have a great tuner i use the tuner built into the yasoo so um this is something where you need to have a really clear signal in order to be able to effectively communicate so i've got samples of this the sample i'm going to play is a call sign of r u3 amo calling cq on 14047 this is what it sounds like it kind of sounds like those old those old 50s space movies when you hear like the space sounds you see a satellite and you'd hear that noise and it's muribah dot code and and that's why because that's what they used to use to communicate so the next thing i'm going to talk about is phase shift keying which is different from the frequency shift keying this is a different type of modulation and there's a lot of different modes there's there's a ton of them so the most popular one the one that you'll hear about the most is psk 31 this was created by peter martinez that's the most popular mode and the chart that i have or the table that i have there shows the different frequencies that are very common for using psk so if you're looking to get into psk or listening to psk or trying to make make contacts on psk those are some good frequencies to try this one's also pretty slow it's 31 bod using vpsk modulation and some of the modes here are very resistant to crowding interference which means you're more likely to make a qso it's not quite as bad as rtt y and some of the modes even have error correction so error correction is great because it it helps you get a better signal and the system at least knows when uh when an error has been received and how to correct it using using the the encoding that it has so there's a whole bunch of different software that you can use for that i've got a few examples up here fl digits probably the that's the one i'm most familiar with but there's a whole bunch of other ones out there really psk 31 was developed to be about as about as fast as someone typing 51s words per minute i type 100 words per minute but i've been typing a long time so there are other modes psk 63 and psk 125 that transmit faster so they would you know be able to accommodate me and really psk 31 was kind of built as an improvement to the slow bpsk which was created by sierra papa 9 victor radio charlie so this is a really neat mode this one's you'll have better luck with this than rtt y and i have an i have a sample of that one here yeah so that one does kind of sound like a whistling with maybe with water in your mouth so if you hear that that's that's what that is if you're you're you know surfing around looking for someone to talk to so next i'll talk about packet packet what we call packet radio in in terms of amateur is really ax 25 in digital and this was first used by canadian amateur radio operators in 1978 the montreal amateur radio club kind of like pioneered this and developed this technology and started using it and it was authorized for use in the us by the FCC in 1980 because we need permission from the government for everything so one of the things that is unique about this mode of is you need a basically a modem or what we call a terminal node controller a tnc so i've got an example a picture up there of one there are a lot of different tnc's out there there are tons of them and there's even software ones there's a great software one called called direwolf that i use and using a software tnc is great because if you have a way to connect a computer to your your ham radio and especially with the ability to do push to talk from the computer it makes it really easy to get online with direwolf and i'll even show a solution here later on for how to do that how to connect a raspberry pi to a radio one of the most popular methods or most popular implementations of this is the ap rs system or automated packet reporting system this is really a system that's designed to report locations to say i'm here i'm i'm in a car and i'm driving and this is my gps these are my gps coordinates and it's kind of a way for hams to to be able to find each other and and kind of share the location like the original four square if you will so you can also send messages and these a lot of these tnc's have the ability to store and forward so if you're trying to send a message to someone and they're unavailable well you can go a certain number of hops and then that message can be stored until that the receiver is available and then it can be sent on and this can happen over the radio it can also happen over the internet so you can connect to the ap rs network with just with software of the internet they require a password but there's just google ap rs password generator and you don't need to ask anybody for an ap rs password it's it's not complicated someone figured that out so ap rs is really great it's good for things like telemetry there's short email messages ask more like text messages that you can send and you know a lot of times it's used by storm spotters and people to share information and say hey i'm out here and there's a tornado or we're having bad weather so that's a great system to use i've been i built an ap rs capable system so that i can do that mobile and most times you'll see this packet mode being used on on two meters so there's a whole bunch of different networks and things that you can connect to i've got some examples up there like tarp and and text net and bbs and other that there's a whole bunch of them sometimes they're regional so check to see what's available in your area there might be a good packet network that you can get on to and talk to other hams and get to know people there and this is what packet sounds like yeah very similar to like the the old Commodore 64 tapes so this is probably one of my more favorite digital modes and this is what i'll be doing a demo demonstration or a demo of later this is slow-scan television so this is a really old digital mode this was developed in the 1950s and if you think back to the 1950s people didn't have computers in their home so how would you digitize video or television and transmit it over the radio and they use these things called viticon tubes to basically take an analog signal and make a video signal and then transmit it over the radio so this was eventually officially approved by the FCC for amateur use in 1968 they used sstv on the Apollo mission the Apollo mission to the moon sent sstv images back to earth for pictures of the astronauts originally walking on the moon so that's how long this has been out there and in use it started off kind of just as black and white but now you can do color and there's there's dozens of of different modes you know scotty one is a popular one and there's one called robot and there's a bunch of different modes and a lot of the software that you can use to decode sstv will do this automatically and you can get software to decode sstv for your phone there's an app in the iphone store there's a bunch of apps on android for it there's apps for windows linux mac os the most popular app i think is mmss tv on windows and you'll see a lot of times when people transmit images you'll see it'll say mms tv across the top it's one of the default templates includes the name mms tv so you'll see that a lot but this is a great mode that you can get into because you don't need a license to receive these images if you're just going to listen you can do that easily the international space station transmits slow scan television images quite regularly and they're about to do that again here so you can get an app that'll tell you when the the iss is going to be over your part of the world you can tune to the frequency that they broadcast on set your phone nearby and when an image comes in you'll you can you can turn on the autostart and auto mode and it'll just you'll receive it and it's it's pretty cool you get messages you can get an image from space over the radio so this is a really fun one this is what i'm going to do a demonstration of later and this is what it sounds like at least one of the modes so next we have mfs k mfs k or multi-frequency shift king um this is one of the uh one of the more popular digital modes that people use today uh and the thing that's that people like about this digital mode is it is very good at transmitting very weak signals across very long distances and the reason for that is it uses um tropospheric scatter phenomenon so basically that means the radio waves at the u h f and s h f frequencies are randomly scattered as they pass through the upper layers of the troposphere the radio signals are then transmitted in a narrow beam aimed at just above the horizon the horizon in the direction of the receiver station so as the signals pass through the troposphere some of that energy is then scattered back towards the alert uh towards the earth which allows the receiver station to pick up the signal so basically uh you know this used to be called skip i think um because you kind of skip along the the uh the the troposphere um there's a lot of different modes for this for mfs k and um the large number of modes makes it really a little bit confusing but also easy to get started because you can just kind of pick a mode and um and gain proficiency in it and then make qso is really easy um so uh there's a piece of software that's kind of taken taken off with this and really made this popular called wsjtx um and if you type wsjtx into youtube you'll find a million videos of of hams showing off what wsjtx do and if you go to a field day there's going to be two or three hams that have a raspberry pi in an ipad or a little laptop um and connected to the radio and they'll show you all the things that are happening on ft8 um ft8 is one of the one of the um mfs k modes that's more popular um so this makes it really easy because you can uh you can send signal reports so you can call for cq and you can send a signal report and then 73 which qualifies as a qso so you can make qso's and log up in qrz or uh lotw or um you know any one of the popular logging platforms online um and there's a mode called whisper or wspr and this mode is more like a one-way mode where you're just kind of broadcasting a signal and the report back that that signal has been heard is made over the internet so once you broadcast on whisper um anyone that hears you then reports that into a central database on the internet and what this is good for is it's good for testing what kind of propagation you're getting um so if you've ever wondered you know i'm i'm on my radio and i'm transmitting i don't know am i getting is is is there anybody out anybody hearing me and am i having a problem with my radio a problem with my antenna is my antenna not tuned and am i getting interference from somewhere is the you know someone next door got a something that's leaking so much rf it's it's bleeding over my radio and nobody can nobody can hear me uh whisper is a great way for you to get on the system you broadcast a whisper message it takes a long time actually to broadcast a whisper message um but you can get on you can broadcast and then within seconds you can check a map um online in a web page and see exactly how far your signal propagated and who heard you so this makes it really easy you can see what what bands are open right now right now for you and who can hear you and um it's it's actually pretty great um so whisper is really good for kind of understanding what you know what your capabilities are right then and there and not by theory but by actual testing so you get empirical data um so i definitely recommend using whisper um especially if you're wondering you know i'm calling cq and no one's no one's responded to me is it can anybody hear me um it's a great way to test your radio and understand what your debt and you're getting there's even a method uh or a mode in wsjtx that's designed to bounce your signal off the moon um so that's just kind of cool to me to think well i can bounce a radio signal off the moon uh and receive it back out here on earth that's just kind of awesome so uh this is what one of the mfsk modes sounds like that what this one sounds a little spooky to me it sounds like ghosts in the ether to me it's just it's just kind of eerie to me but um yeah it's interesting uh rathion has been using mfsk in the military for quite a while and they've developed an mfsk system for military use obviously they can make a 100 megabit per second radio link over extremely long distances through the troposphere so um you know there's there's a lot of potential with this type of technology i'm sure they're never going to let civilians use anything like that anytime soon but um it's kind of cool to know that capabilities out there so if you're kind of interested like in getting into some of these digital modes and some of these data modes especially one of the things that you're going to need to be able to do is connect a computer to your radio and by connecting the computer to the radio you're going to need to make kind of like three basic connections one is um audio in the next is audio out and then finally you're going to have to make a push-to-talk connection what that means is your computer or your tnc or whatever device you're connecting to the radio needs to be able to control the push-to-talk uh so there's a lot of different ways to do this um you know some use serial ports and you turn the clear to send or ready to send on and off and that that triggers your push-to-talk but most radios a lot of radios at least have just basically a hard wired connection that you can short to ground and that turns on push-to-talk so i bought a really kind of old radio at old uh can this old kenwood radio that's a two meter radio i think it's 25 watts maybe uh yeah about 25 watts if i remember correctly and i got it for $15 and part of the reason for that is if you look at it um there's no way on this radio through the the the knobs and dials on the front to enter in a specific frequency all of the frequencies that this radio uses have to be programmed using a serial using a serial cable a programming cable and it uses this really proprietary connector that connects onto the front you can kind of see it there in the photo um let's get this round connector that's proprietary um and the you can get the programming cables that for about 35 40 bucks uh and then you have to have you know uh their proprietary kenwood microphone which again is you know another 20 30 bucks depending on which one you buy and um so a lot of people so this radio it uh it sold for $15 it didn't have the the proprietary programming cable with it it didn't have the little uh the uh the the microphone with the proprietary cable it has a proprietary power connector on the back and a db25 um and just a standard kind of uh u h f style antenna connector um so these radios don't sell for a whole lot of people that sell them don't even know how to test it or turn it on um one of the one of the interesting things about this radio is they're designed to be used in vehicles um so there is a uh a mode that you can turn on or enable in these where it won't turn on even if you plug in the proprietary power cable it won't turn on unless uh an extra power is an extra power signal is applied to uh the uh basically the engine on signal uh for the radio that indicate that that the vehicle is started and running so a lot of times these things are sold as dead but they're not dead is the person just doesn't know that um that tested it so i got this this thing for $15 it works perfectly fine um i tore the proprietary connector out of the back of the thing put an anerson power pole power connector on it um i hardwired it so that it doesn't need the the vehicle sense indicator uh and i i also soldered on uh two two wires so that i could program it using a ttl serial cable rather than buying the $40 proprietary cable and there's some open source 3d printable solutions for that that have little circuit boards and i just i looked at that and i said you know that's that's awesome i love that people do stuff like that but it was just way too easy for me to just solder on two wires onto the onto the circuit board and program it that way so that's what i did um and what i did was i programmed in the aprs frequency first um what i when i uh when i downloaded the list of frequencies it looked like this was used as a in a fire truck or some kind of a um a fireman's uh vehicle uh support vehicle or a fire truck itself it's very dirty and i had to clean it um but anyways uh one of the things that this radio has is a db25 connector on the back and uh the documentation for this radio is online and you can go find out what all the pins are for the db25 and the db25 has uh an audio in and an audio out and it also has a push to talk pin and when that push to talk pin is shorted to ground that enables push to talk so i'd said great um and that makes these specific kenwood radios really easy to connect to something like a raspberry pi um so i wanted a quick and easy way to connect to my raspberry pi so i designed this little very basic uh circuit i bought a uh what's called a prototype hat for the raspberry pi on amazon i bought an opto isolator or i had an opto isolator from probably from either digiki or mauser one of those two and uh and a 3.5 millimeter jack and uh you can see the the diagram that i made there um i have in the in the schematic i have a gpio 18 connected to uh one leg of the the led part of the opto isolator and then basically a resistor connecting back out um back to back to ground so what an opto isolator does is an opto isolator allows you to close a connection but have that be electrically isolated so why that's important is when you're connecting two pieces of electronics and you're shorting things to ground and making those kinds of connections there is the potential for electricity to leak back you know and we can put extra diodes places things like that but really the safest way to do make that kind of connection is to use either a relay an actual like physical mechanical relay or an opto isolator or kind of like an optical relay if you will um and an opto isolator basically has inside of it has like a little led and a little um basically a photoresistor so that when the led is on the circuit closes and when the led is off the circuit is open so on the other side of the opto isolator i connected a 3.5 millimeter jack and i wired i wired up the the cable that you see there on the bottom right corner i wired up the appropriate connector for audio in and audio out i connected that to a usb sound card which for the raspberry pi it does have the ability to output sound but it doesn't have the ability to input sound so you really do need a usb a usb sound card for that and there's a few really cheap ten dollar usb sound cards i think i used a cyba syba sound card and i think it was like ten dollars they're really cheap and then i wired up another 3.5 millimeter jack for the push to talk and i wired that up to an old parallel printer cable that i lopped one of the ends off we connect that to the back of the radio and that allows me to control push to talk by toggling the gpio pin on the raspberry pi for me i wanted to get on aprs so i was using i'm using the direwolf virtual tnc software and literally one line of of code the configuration to say use gpio 17 or 18 or whichever one you have connected use that gpio pin for push to talk and then direwolf those when i need to push to talk i i toggle gpio 17 that's push to talk so and so that makes it really easy and since i used a jack here just a 3.5 millimeter jack i can make a cable a similar cable for another type of radio if i had you know say an old yesu or or something that had a similar style of push to talk that that's just basically it just needs a a switched on you know shorted to ground type connection that make that very easy to connect you could even do do a similar thing where you have two of these opto isolators on two on two separate gpio pins and for some radios they have the ability to trigger cw cw the transmission of cw so you could have two of these with with two connectors and you could not only enable push to talk but you could also trigger cw so you could just have the one can able connect the cable connected and do both of those so that'd be really easy to do this is a really simple circuit i know it doesn't look like a whole lot but it doesn't take a whole lot it doesn't take much to do that so i highly recommend giving that a shot one of the things that some people talk about when when they talk about connecting these radios to the usb sound cards they're concerned about isolating the audio so the audio in and the audio out i didn't do that in this case just because i'm using a little usb sound card and i'm not super worried about it if the radio melts the usb sound card i'm not going to cry too much but if you are worried about that an easy way to do that if you don't want to build your own kind of you know audio transformer circuit you can buy what's called a ground loop isolator and they even have ground loop isolators that use 3.5 millimeter jacks on each end so in this case i could just buy two opto two ground loop isolators they're like eight bucks a piece and i could just hook those up in line and that would solve the problem of of isolating the the audio and an audio transformer is basically just two you know two windings around a common you know ferrite core so that also electrically isolates one side from the other so that you don't have to worry about voltage spikes taking one or the other device out for me if you're over modulating it's super easy to just in in the digital mixer just turn the sound card down so if you turn the sound card down then you're then you don't over modulate if you're you're too loud if you will so that's that's kind of my simple diy solution my circuit for you there the schematic and everything as well as this entire presentation is going to be available on my github so with that let's get into the demo so i'm going to pause my recording here and then i'm going to switch to the demo welcome back so what i'm going to be doing today is a demonstration of a slow scan tv qso i'm going to be using an ipad and i'm using a ss tv app on the ipad i'll be doing the the transmission and receiving on the ipad the way i'm going to do that is i'm basically going to use a very simple bofung radio the bofung radios can is tuned to one four five five hundred just using basic simplex not using a repeat or anything this is a very common frequency that's used in north america to call cq and transmit images on ss tv you can do this with a technician license and you can also just monitor this channel and use an ipad or an iphone to listen to see if anyone's broadcasting ss tv images again you don't need a license to brought to listen you only need a license to broadcast so i'm not even using a cable or anything i just have my my ipad here and you just hold the radio close to the ipad and you can use an iphone for this as well or an android device there's a ton of apps on android but i've got the uh i've got the the view of my ipad up on the screen here so this app is really basic some of the more advanced apps like the ones you can get for linux and windows and even mac will actually transmit cw at the beginning and end of your of your transmission so if i'm using an app that doesn't transmit cw i'll just get on when i key up i'll announce myself and then i'll start the the ss tv transmission so let's go ahead and do that i'm gonna call cq and then my my father-in-law who is also a ham operator is going to respond and then i'll love i'll do a 73 and and give him a signal report and end the qso there so let's go ahead and get started this is k4 chn calling cq via ss tv so what i'll do here real quick i've already got this set up to transmit this image and i'm going to go ahead and start transmitting okay so one of the things that you saw me doing kind of at the beginning there as i was uh moving the image around that what i was doing was tuning the the phase in the skew this app can actually decode at the same time as it transmits so you saw that image come in and i was just adjusting it a little bit so i could monitor the progress so once he receives that image once he receives that he's going to build his own reply image and then he'll send that back to me and we'll see that here go ahead tg5 teu he's going to go ahead and send me a 73 back so uh the auto start didn't kick in for some reason that time so i went ahead and hit start so that's why we've got a little bit of the image missing off the bottom there it's something to pay attention to also think about uh when you're transmitting make sure that um you're not putting too much data at the top of the bottom because a lot of times that gets cut off um also while i was receiving i was adjusting the uh the phase and the skew um so this what this does is it allows you to kind of tune because it's it doesn't always get started perfectly and it doesn't always hear it perfectly so now that we've received his reply let's go ahead and build a a a receive report and a 73 image so what i'm going to do is select an image um so i've got an image ready to go here uh i'll build my reply text and then let's take a preview that's the image that i want to send so now let's go ahead and transmit that image so that's uh just a basic example of a qsl on sstv you can do this on uh on simplex vhf like i did here uh you can also do this on hf um and if you're watching this video later you can actually hold up a smartphone and decode this the images that i transmitted as they're they're being transmitted here out of this video um this mode is actually a lot of fun um i monitor 14 230 a lot um i use that on my raspberry pi um i run the uh an sstv app on in linux on raspberry pi and just monitor and sometimes if i don't want to get my raspberry pi out i'll just turn my 991 on and and set my iphone down next to it and see what i get um i also use a a t-ton of a shortwave radio that can receive a single sideband and sometimes i'll turn that on onto 14 230 or some of the other bands depending on what time of day it is and uh and just set my iphone and see what i get so this is a lot of fun you don't need a license to receive again um you can anyone can monitor the radio and see what images are flying around out there so that's my demonstration i hope you enjoyed it now back to my presentation so thanks for attending my talk if you'd like to stay in touch with me uh one of the best places to stay in touch with me is on on my github i'm also on twitter uh as at j marlar although i'm not very active on twitter um but uh github is where you'll find uh this presentation and some of my other open source projects um this presentation is going to be available at that link in pdf and html format um also you can email me at k4chn kilo for charlie hotel november at arrl.net um and i'll be walking around the conference um and i'll be in the ham radio village so if you're going to be on site in vegas uh i and you want to stay you want to say hi please feel free to stop and say hi and uh if you see me on discord uh please feel free to to say hi on discord and ask me any questions you have um and if not i hope you have a great conference thanks