Pragmatic 64: Software Radios

10 October, 2015


Pragmatic returns to talk about a recent melding of traditional radio technology and software that are now dominating the telecommunications world.
Transcript available
Welcome to pragmatic a discussion show concert playing the practical application of technology by exploring the real-world trade-offs we look at how great ideas are transformed into products and services can change our lives nothing is as simple as it seems pragmatic as part of the engineered network rather great shows visit today this episode is brought to you by it's a pin pair in the iOS and shopping shop is a free collaborative shopping list at that simple and easy-to-use and will talk more about them during the show I'm your host John Geagea and I enjoy today, co-host Carmen Parisi is going come in pretty good JW very good very good thank you so the yes so I just wanted to before we dive into today's topic which will be software radios artist will have a quick discussion about what's happened in the last six months so when I wrapped up dramatic about six months ago I actually had no intention of bringing it back at all I think it a precognitive job of wrapping it up actually and I didn't I underestimated significantly underestimated just how hammy people that annoyed and dumped by a defence of the show were very very vocal to me and I continue to get emails about you even this week and just asking about ways I could bring the show back somehow just even doing it less regularly or something you are getting more help with the show summing like that so I idealist soul-searching and is over last six months and I decided that what I think was lacking wasn't just pragmatic as a show but it was the kind of content that I think that pragmatic offers which is sort of focused engineering related content and as I tackled the waning attacker problem and and I guess that's what I felt was was lacking in in the pod casts space for some out there that are scattered everywhere and I looked for networks that would support a show like this and fundamentally I did I couldn't find any go looked at confining so being crazy I decide to start my own and I'm calling it the engineered network or 10 for short now it's a small network and for now and may stay very small or it may grow will sue happens either way I ever find out the rest wealthier or whether this will feel the same way I do a guess at any rate in order to keep making the show pragmatic I've cut the frequency to show back to once a fortnight which many fans suggested so I'm taking on board and I do once a fortnight are Carmen will also be are helping with show production for me and I'll be starting a second podcast called our causality and causality is inspired by episode 11 of pragmatic a lot of good feedback about and I really enjoy arm cause-and-effect so this link the show notes with more information about causality for free have a look at that others may not show at the launch of the network called nutrient and other support cast by two chemical process engineers enable running website of the same name for several years now and site mostly really excited not just to bring back pragmatic and but also bring teach to new shows are to listeners pragmatic that they that I think they will find really interesting now both causality and injury will be launching in the second half or week of October and all the shows and the network ago produced fortnightly soap are the network itself the ad arm the URL for it will be is and data is also a newsletter you can sign up to our give you are an update every weakest evidence happen that week I'll also be a store coming shortly with a few bits and bobs in its and there will be a patriot on account you can contribute to as well if you wish to be rolling out shortly so they go so we are back and is now that's on the table artist also say that I'm currently open to exploring new shows so if you're interested in making your own pod casts solo or with a friend or a group of friends you're practising professional engineers then you please get in touch by the contact format and will see we can do ripening is another that I was a dog on a topic, don't you think Shorey and honourable people of all the other the other stuff so arm I want to talk about software radios previously I talked about are to a ready a few times episode 39 as well as episode number five Axa going way back in time but I never really did much talk about modulation and demodulation and that's one of those things that are because of your background and experience of arrays actually in before we dive into that meat commuters give the listeners like a couple of minutes summary of of your background and an expert just explains that they know where you're coming from Shorey and a problem are so I'm an electrical engineer and a mini analogue and semiconductor industry applications engineer working on no switching regulators forearm Intel the core applications so the men price is a voltage that is older yet on your Intel processor runs on a mixture of pirates submitted longest distraction Intel puts out transient response selling time efficiency targets you name it day I have to meet it are which is interesting because it's easier said than done sometimes especially on these new scaly designs for tablets there are motherboards the size of Dakar is almost and you are just a few more capacitors on their blood do that you need try to make 20 amp bar 20 and transience with six or three capacitors it's it's difficult with things like Tseng bite anyway skin to deepen their as I studied now so study like wandering Carla decide to have my masters degree and a Didion medications as a focus I was building hours some hardware for a radio to encrypt the channel using the randomness of the carrier you need we worked on paper and made my circuit work but the bits of Stendhal did note decks do what may our teacher expected also to tell them that it is unlikely that INRs is so honest I screwed as fine as fine as eloquently could be my circuit either worked only to schematics and memorials young and inexperienced main everyone's hand everyone enthusiastic everyone's design a circuit hasn't worked and if you haven't well as you hang on, and ambiguity have I have iMac of design a couple that didn't work but that's okay that was a long time ago and I also claim that I was young and lower social good no judgement yes you have 1/3 revision I do things much differently you just one more spin of the board, will do it again talked with Final Cut - that's only need revolutionise everything because we well first pencil I need pate what it was a Nortel and they said arm we have to spin the board the collective groan in the conference room was just unbelievable because these boards on them like 12 layer stacks and the like God we spinning a 12 lab earlier sausages love to hear about to change the layout when it's almost reduction and you notice this rugged since I next the noisy fees note here that is because in the areas that were barnacle on there should be fine ship at spine than a for another modern no problem lawyer it's fine how exactly anyway Oracle well thank you for that at least every one has a better idea of the background outlook on a topic about my background because if you haven't figured out by listening to pragmatic the last two years then you properly you are like myself self bits and pieces will show up during the show while the cool alright so arm that I carries and are modulation size must start with the very basics and I guess with carriers and modulations are carried as mean single frequency or a single frequency over a certain bandwidth and is essentially modulation is about carrying data and using a radio to carry that data radio wave carrier to carry that data hence why they call it a carrier is its carrying anyway arm although not like someone carrying a bucket of water but never mind so anyway modulation the most simplest way of modulating a signal is to simply turn on and off in a sequence of no no no sounds like pulses are didn't ask for example and that's the Morse code essentially and as were also started with modulation technology so are the idea is that you would Morse code return the carrier on and off for two different our durations and that forms data in groups and in the space those groups apart and they form letters and obviously then we space of slightly more power to make words and hey presto you're communicating our aids slow it's inefficient and yes but it works the technical term unbelievers on asking are yes knocking that's true i.e. the funny thing though is if you really want to break it down it's kinda like a try states time the main serial data transfer mechanism thought about how would you classify that's how you would be its three states you off which estate one did which is a short sound that statement to an Dar is state number three such technically tri-state and it's all done the time domain so time and tri-state serial data transfer we will call Morse code though because of Samuel Morse and all that type that happen okay they go fantastic Morse code art but analogue modulation or a.m. is far more interesting because that's can carry armed things like what no our voices that say and are the idea is that if I sent a carrier and I various its amplitude are that is to say arm yes its amplitude when analogue waveform over the top are then is really simply stripped the carrier off and you then have an analogue waveform that sounds like the voice that originally started it by was originally modulating our it's it's so easy and that's why analogue modulation a.m. was the first kind of far radio technology that that carried voice and music so you decoding is easy you can indicate is not crystal red crystal radio when you're a kid rumours about I didn't know judgement I did not know that I have built what are those are the civil science projects for kids whatever reuse ago a penny in an hour: BAA. From the house you can builder an analogue demodulator yeah those are cool in our dominant those I had a crystal radio set to which I promptly broke within a week that's okay are yes but yes I did have one of those and I visited the whole arm try remember we don't have pennies but anyway it was a coin it was a kind of some kind of forget the denomination but anyway yes and exactly we talk about but anyway the big downside of a.m. though is that while it picks up noise and I'm in my atmospheric noise and if there is a popular collector like a lightning strike all sorts of different things and all that noise gets picked up buying the signal though so your AM signal start out as this pristine beautiful modulated thing with your voice honoured by the time we get to the other end as is got all sorts of rubbish in there and as a result it sounds well terrible oil yea it was good back in the day when I saw you had it was that nothing and the wireless in I was a big deal but obviously we could do better and we did better because that swimming can't with the figures in modulation or FM and a good thing about FM is that our because the frequency so that if you imagine a carrier frequency let's say I'd know hundred megahertz and if you do vary that frequency are plus or minus our 10 kHz or 20 kHz are based on are the intensity of the audio going into it you are essentially modulating that carrier frequency are with are the audio information from the musical from your voice and that is completely unnatural and that the blood is not my main one is that there are no naturally occurring frequency modulated radio sources so if you atmospheric noise arm it will not it will not affect the frequency modulated signal so the FM signal essentially is all the same amplitude so that means you when and that's great right because that means we we get real noise problems as well is not FM radio it's beautiful crystal clear size sets also are truncated when you pick it up in your current rate because has started to spread the frequency can't turn out any account recreate all that CF depicts a certain power level that recreates the idea enough yes it is the benefactor trainer in my communications class yes night and that that's that is that is exactly right and that's why FM will drop out much earlier than a.m. so if you're the same distance away from the radio antenna and this is notwithstanding the frequency problems with the old ionospheric propagation and and are bending around the Arabia horizon but beyond those effects point to point you will get AER you will get your ear will be able to decode and hear a.m. rather than FM it with the same amount of attenuation because of that because it has to pick out that lowest point work and recover all the data and that's why FM tends to drop out as opposed to fade so a.m. tends to fade FM seems just like dropout and shop night chopping sort of unhappy describe that George was sound effect sure fifth bigger that's my firm dropout noise okay RA Hall are recorded as can be on a pragmatic sample are so God please know and make a soundboard to the show will just be me saying anyway and fantastic and that sound unit is physical host Williams got the working morning DJ some draft if you make a soundboard year will talk later alright so now there's actually a really good animated card gift Jeff whatever GIS on the wiki page are about Translink and the show notes check it out if you're interested are because it sort of shows better than I can describe with words and this is was one of the problems yelled on the show try to describe with words which is easier sometimes the drawing that they have it we were working with what we got alright so that's FM in a nutshell our phase modulation is kinda like FM but the phase of the carrier is modulated and that's even harder for me to describe with words let's just say yeah phase modulation and move on because well unless you got a better way of labour showed a better way of describing it but I can see that I do now league okay lovely let's agree to move on are okay so let's talk will be about narrowband are versus wideband because you may have heard me have maybe haven't are the expressions I guess that when I look through the Wikipedia entry on this I wasn't completely happy with the description but here's the description and the gives the channel of communication is me paraphrasing channel communication when the bandwidth is narrow enough that it's frequency response is essentially flat from the start to the end frequency and I guess the problem I've got with that is that it's like the frequency response of what you know is it the amplifier is that the antenna is it the mix says that the what the hell is a discriminator were depends on what signal is buried in the sea I think it's a very is a very generic and non-specific statement I think that is far better to say that we roughly use about 25 kHz and everything is relative so you could say that compared with 25 kHz signal a 5 kHz bandwidth signal is narrowband compared to 425 kHz but then again you look at something like spread spectrum signal forearm yellow LTE or something that's you 10 MHz wide or something insane then 25 kHz looks like it's narrowband compared to 10 MHz site for Garcia was in the travelling it differently when you said the channel of communication I statement the channel itself what you are doing the challenge is not familiar with spell caveat with spread spectrum FIP fodder pick channel one then on LTE than channel 1 you would be could be 10 MHz wide and 5 MHz wide you depending upon truly eight so that's a channel and that's jungle spectrum that Sprint saw AT&T olio Telstra whoever they are will will pay and say a cable I got this frequency band and I got five channels and out I can use whatever I want you whereas you hope it will narrowband staff is its it's broke its side doled out in very very small bandwidth like you if you think about some fixed terrestrial fixed radio and I go and pay for a license traditionally is relative for telemetry systems Landry systems can be operating at 430 MHz or 430.125 while you get a license to pay a fee for a home for 33.125 the next channel is the fourth fourth 33 points arm 250 traders met in my head guy should be doing is my head I need a calculator and engineer anyway point is are yet to overkill as that was a narrowband channel and I think that a lot of stuff is now going away because of spread spectrum and yet a lot easier way frequency frequency overlapping the spread spectrum that's great to piles on top of the negative big mess but of minor why my talk about this until it is because our it's in its sister are important to understand the difference in the effect of the data rate and were beginning to modulation technologies and different things and we start the radios that the bandwidth kinda matters its it's part of the equation so arm wideband essentially a sort of stopping but honestly when people say wideband these days they really talk about spread spectrum and spread spectrum is really wide like I say before megahertz wide so owner ideas throughout another ballot I dunno what else there is doubt about it was a was a very vague definition if we agreed and disagreed at the same time you did we think we did well anyway there have okay cool now get into the interesting stuff and while I came more interest some draft yet-I think it's more interesting okay this is a modulation arm technique and there's a couple of an icon overlap in some ways this subtle differences between them but again Q IM R quadrature amplitude modulation and is it's our friend cousin relative whenever brother are QPSK which is R quadrature phase shift keying so the idea is arm let's imagine you've got to carrier signals in each carrier signal is 90° out of phase with each other so when waveforms are because everything went to mass or sine waves so sign way started 080° you go to 90° and you are there at our positive maximum ego hundred 80° the back to 0 gamba head down and then you go to our 270° and their maximum negative and then go back to 3 ago 360° or sooner zero are your back is zero again in this oscillation goes on indefinitely bustles your carrier is a sine wave I'm assuming listeners know what I describe my/sine wave I hope so so if you put to our 9° out of phase with each other and then you can keep them on and off together at the same time or part and then you vary the amplitudes of each carrier as you doing that what that can do it without subduing as it creates essentially like a constellation are like stars but more organised anyway and doubt what you can do is on on X and Y axis you can actually plot these and again Wikipedia page link and the show notes is a great animated GIF gift Geoff GIFs that shows are the consolations they can have like they were usually called by the number of points and because everything is based on binary are you so binary in in both dimensions so you'll have are zero and one and in 01X01Y which will give you a maximum of four possibilities 000011011 and a because you did you go up in in those multiples so you'll go to our God to eights to 2 hangar so for a God damn it's for a 16 3264 thank you that's what I was tired yes you should have written that down but anyway but yells it to her exactly so thank you very much arm saving so Mary okay so are again great animated ad GIF the Wikipedia page does that shows this now armed women to matters before you so there are a couple of our IR like they okay so how about you talk quickly about like-minded IQ modulation which is related to this short solo IQ modulation like you said you start with a sine wave you generate another carrier that is 90° out of phase switches cosign with if you want to go in the most basic sense arm and you do this so now there's a couple shift register as you can make a quadrature isolator it's cold and so you mix in your information signal the carrier and send it out and are surely decode it you know you get through our traffic and easy way to do this/the videos I guess that's arm power man sell depending on how you vary the amplitudes and the frequencies in the phases of the I think you are either standing for in fees Q standing for quadrature on you can recreate in order amplitude modulation frequency modulation the fees shift modulation that we talked about earlier on and it's relatively simple I guess arm so for example if you doing are nearly try new Q in your demodulator and you see that there are 30° or 30 kHz difference in an office 30 kHz above or below but because you're the only Q depending on which one needs of the RA is leading it's 30° above benefits she was leading it's 30° below I believe that have that backwards well I'm not entirely sure if that is backwards I thought that Senate correct but in any case arm there was a couple of good tutorials that you link to the YouTube video and there's ours link to analog zoo I think it is about analogues earlier yes so those leaks will be in the show notes if you want to dig into that little bit more this one is a little more about base of the ball the little mouthpiece for the cholera from different are different approaches Allen's star Alan Wilkie W-2 EW are new to our new covers it more from a colder practical arm approach although that's in another analogues it is impractical because of more practical approach and explains IQ modulation and then our Craig of analog zoo delves into our oil is equation and is nice for those gas arm's another that is impractical but it's it's moving some of the listeners haven't seen that map before but it essentially relates exponential is to our signs in cosines and is the foundation for prematurely electronics these days you absolutely rights of and doubt when I was harassed at about quadrature leading following the ER in fees signal I was referring to the oil is equation which the imaginary term with the Sinai net neither its plus jail plus J sign reminders to sign jewel are any other thing about Alan R and Darcy's W-2 EW I think this is callsign season amateur radio operator gasoline header Micronesia the monitors frequency bands this up around on his gutters, outfitted with the radiology travels around the US selling oscilloscopes are really cool you were here as a fellow radio amateur than arm yes I could I would highly recommend mice that's cheating but anyway yes that is good I had had had a look at it was very nice so right you're so arm another bout IQ modulation I guess for the moment are I want to talk about is our mixing and into modulation just just quickly and it's important to understand that there is there's limitations to all the gossipers were describing is wet when you're stripping off the carrier however you doing words on IQ modulated signal FM modulated signal AM signal doesn't matter all of them have the same problem the higher you go in frequency because the higher you go let's say you're your view carrier signal is army a 1 GHz well it wasn't that long ago that it was impossible to directly sample 1 GHz and the reason I say directly sample is that if you're modulating a signal at 1 GHz you need to be a sample all the data at least are twice that rate in order to see Negros criteria the exactly that's right and because you need to be able to sample and it makes sense when you think about it right is if you got a sine wave how can you determine the period of that that that sine wave unless you take two samples in its overall. You don't know when it starts and finishes otherwise so that's the basic way of thinking about it but the truth is that the way the people of gotten around this for a very very long time and frankly still do a lot of cases is our mixing so how mixing works is if you get tooth to frequencies very different and you mix them together you will get into modulation products so you can get the sum and the difference as well as your two original signals so popular signal at armed 10 MHz and I mix it with 100 MHz on end up with 110 MHz is a byproduct more sickening get 90 MHz is a byproduct plus my original 10 and the hundred and that mixing and in the into modulation product sometimes you avoid that but this particular case would you try to do is you try to step down that frequency to something that you can sample you are down mix that to a point at which are or down convert will have you think about it are Tutsis or fricatives you can sample that you can actually extract with with components that are actually that actually exist and I deny her CIO frequency correct yet intermediate frequencies exactly and the typically value having a local oscillator the local oscillator will will be tuned to a specific frequency to down mix that so that you can then adjust it what you're listening to and that will that and then what you need to do is you have to put through a filter of some kind so that then is leads to bandpass ban stop filters so if you've always got a local oscillator of specific frequency you can actually tune that out with a ban stop filters say that it will essentially allow only signals through old depend on your role often the bandwidth that you that you've got it all in advance of bills will essentially let everything except that the small narrowband you try to selectively remove are the other pop sabbaticals bandpass filter of our bandpass will only let through the frequency particularly that you're looking at so what typically will do is you'll you're down mix the signal and then you put a bandpass in the region that you're actually able to samples of your down mixing a gigahertz and you down mixing it through a through multiple single stage a multistage armed receiver and his dropper down to say maybe you know 10 MHz 20 m I know whatever frequency or less are the new display bandpass filter to sort out that one bit so that all the high-frequency staff and into modulation products into my adulation frequencies will be tuned out by attenuated by the bandpass filter and that is the signal the actual sum to people referred that as the baseband eventually dropper back to baseband and you can accident sample that and away you go and was a sample that I guess I'm jumping ahead of myself as the topic of this is ipso software radio so obviously you we can be doing some analogue to digital conversion and sampling but in the traditional sense that's just how radio receivers work in the most popular in the last site and know what 5080 years long time has been know that your conversion to Betadine receiver are ordeal conversion super short is actually not that much shorter can think of it anyway so yes and you think you had they caught something like that the D had someone that would be DDC had no category good mammal regularity actually that's it and get on those sinners were done okay 80 years too late as fine anyway so I see at the devil you have your conversion to Betadine receivers are built a couple those myself arm one of them was part of the NN one GER transceiver that I built many years ago and see other great they were great however are that's not where you talk about those the principles behind our how we deal with this problem of going higher and higher in frequency and it's great we want to go high-frequency because that means that we got lots more bandwidth and more spectrum to deal with every is going high-frequency right so that Wi-Fi are added to 11 N you're looking at some 2.4 GHz they gets congested we got the 5 GHz when it gets congested with regard to 10 or 15 or whatever as you go up in microwave will be see the radiators and the reasons that pass through solid objects very well if at all but that's okay in small areas and everything is going that way Mike micro cells and pico cells nice or good getting off topic okay direct digital synthesis which is going the opposite direction just quickly and then will startle Medea space so are due to our direct DDS at all you are sure so in the context I know of direct digital synthesis on Melanie when you want to make a sine wave of course a way of trying the wave some sort of waveform armed the city doing it using analogue techniques read start with an oscillator either assign a squirrelly vice leader and shipping the waveform to its desired frequency and amplitude not at stuff using a bouncer other analogue techniques are you using lookup table or a RC of some memory cells to hold the parents of the waveform and you sped out of a digital analog converter and then you just low-pass filter to remove the elder switching artefacts from the DAC in very well ready-made signal gas to the beauty of a DDS is that you can get a lot of excellent precision and control and that's awesome but once it's been synthesised then typically your still go through a local oscillator stage to step up to a final frequency because the DDS is the same problem and the DAC is a same problem as the ATC because you can only sound sample at a certain rate so there is an upper limit to how much you get how how high-frequency can directly synthesise busy switching rates gets too high here and because you still need the low-pass filter and everything to time now to get rid of the switching artefacts is easier to do that a lower frequency building the filter becomes much much easier now is a very good point to actually quite right so I just want to just throw that in there because all these princes were talking about a work in both directions so software radio is a software radio software radio is Job can work as a transmitter as well is a receiver but that worker primarily talk about is receivers but it's important just to clarify that yes DDS is do exist yes and they are kind of a form of software radio sense but some anyway I'll leave it there because I think the DSP anglers as is more interesting okay you know before we go on I think we should talk about our sponsor of this episode and Dar and SAB impair now saving pair decided after years of being frustrated with to-do list apps when I shopping to create an iOS app that the iPhone it's called shopping it has lots to do this apps out there and that people use a shopping list and I know because I've used a lot of them and it is the not very good is because when you go shopping is a very specific use case for a list and an app that is tuned to actually making and shopping from that list into a far better job than just a to-do list on its own if you shop with more than just yourself 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sponsor for the show and the network thanks again arrived digital signal processing in sounds now on local Draeger services this is your domain here in our dear okay fine well then DSP is first of all I think it's important that we understand our the idea of how what if okay visible spectrum analysis so when our signals go past us and we look at them on so I can oscilloscope it shows what we call the time domain which is as each moment goes past every second every hundredth of a millisecond goes past we take a sample and it shows us the in the year amplitude at that point it at the time domain representation can build that up as a trace on the screen you know and is yellow present my digital sampling oscilloscope and you consider trace go past and in Scala Yeo's cousins example I could trend the temperature could trends you no fan speed what motor speed no flow gas flow airflow waterflow whatever and these trends are all time-based trends time-based our signals time domain signals but what a Fourier transform gives us the ability to do is it gives us the ability to convert that time domain information into spectrum information because mirth the Ferrier with the whole basis of of the Ferrier is that you can have with an infinite number of frequencies you can combine them up top of each other to create any time domain way form that you would find a given infinite number of calls and what when I go create an infinite number but the theory then works in reverse so what we can then do is we can take time domain way form and we can essentially extract from that the component frequencies and intensities and amplitudes in order to then recreate that signal so we essentially take the time doing signal and can extract iCal is made up of a signal at 20 kHz one at 45 kHz 100 kHz and one 910 MHz whatever you are so that analysis is that essentially breaks time to messing down into a signal spectrum so that makes sense I'm thinking I'm hoping you seem sorry to metaphorical the goddess of that is yet there are nutshell you can recreate any way form is the sum of an infinite number of same waves eager exactly so there is this pointy nose so give Geoff's online that you can work out to you explain that a little better yester underactive to yes there is some listener shines again arm feel free triggers of your dig more into it I'm knocking out a mass behind arm for is transform the ring and I guess yelling is what we point out there is the term free transformer, refers to both the frequency domain representation as well as the mathematical operation itself that associates the frequency domain representation arm to a function of time that makes sense so people use a Fourier transform in those arm both parlance is so thereby valid I guess but anyway arm sometimes you hear things refer to ours and as you heard that he referred to as is FFT's are fast free transforms which is an abbreviated form or approximated form of a full Fourier transform so arm FFT CEO that was codeveloped in order to make it easier to compute great yester of you using the computer is exactly yes because if you're trying calculate everything down to the last order than you'd never finish and that's the whole point inside that was an infinite number you need an infinite arm using the most significant 10 not even 10 sometimes but that's not really the point only guide FFT is in the open any of that vector mattering us established and that not well-managed and that but that's as to deep today I think okay so where do you start you start with sampling and that is the analog to digital converter so taken analog signal and we sample that and how we sample that while there is multitude ways of doing it but just real quickly are what we do is we will let lets you know I'm going I'll either that's another certain itself the right apologists you know what you right under is not a touch that because there's actually quite I was about to start I thought exactly quite a few ways of doing it so let's not let's assume you have our to 3 textbooks just a matter here you not wrong aright so let's leave it there then I gave the widow the numbers getting right so let's just assume that that's all good night you can now take it signal and go… And I now know exactly what voltages are what time Annabella was beautiful string of data on a ransom FFT is on it and I spit out my frequency domain information hold that thought little bit history because I have to have some history in here because I just love it why I don't know anyway first DSP was actually the TI 5100 and TI meaning Texas instruments of course are those released in 1978 to 2 years after I was born are although technically argue the first DSP was I think arm was developed actually the year I was born in 1976 the kind I thought I was a unified and the alien ship and rise well just reverse engineered our documentary Independence Day honour this with the at that was the that's what I admit I knew I got something wrong about that show skull and cross bones in the damn computer I will never ever ever find really really that's the virus looks like people is a skull and crossbones honours green golf course fine anyways the show is complete now we far made fun of Independence Day so are those Liz 978 arm fun fact about DSP's most DSPs only do fixed point maths or maths or mathematics. He would think about not floating point and it's interesting because the precision provided by floatingpoint is generally not required and because floating point maths takes longer than in the interest of speed most DSPs will stick to fix point some dates I thought was interesting and right now as DSPs become more powerful faster lower power more computations per second it's been possible to use them to directly sample higher and higher frequencies and that's why that's relevant because that then leads us to a point where we don't have to down convert absolutely everything or if we do not not so much and we can actually sample wider and wider parts of the spectrum and that leads us to software radios and when I say software radii guess I mean you were using our firmware which is just you and I hate this distinction between you know firmware drivers operating system my Kernel through the kernel in their home in Casey and operating systems and the amount you inside it seems like an arbitrary distinction understand why I guess to some extent people like to break that down when I say firmware you know I mean it's like digital signal processors have a program to tell them what FFT's run on what and how and what to shift away blah blah blah right that is essentially software defining how the DSP cranks out what it cranks out and that is Geoff Dan generally referred to as the firmware for the DS that the aspect and these days because we still are still in a flash which is great because flash RAM can be reprogrammed which is very cool now in smart phones I guess I kind of sort of note times into something modern that we will use now hands well not all of us but many of us now use now hands got multiple layers of software like I talk about is the operating system's iOS is technically the Apple operating system on their phones and android for example covering system on a Google are based phones however at a baseband level I saw the baseband before but baseband in the software sense and this is a whole problem with baseband because baseband is a radio term before they hijacked it nevermind that arm so involves John that what that is or maybe it's just like our what's the word con they they've conflated one or they have made one convoluted through their conflation no night with a crumbling explanation hard nice crests in goodness many words that they communicate so that a baseband level arm Qualcomm have the thing they call the Rex real-time kernel now I she found some interesting slides about this are reverse engineering a Qualcomm baseband and they look an iPhone 4S and how that set up and it's actually really interesting struggling in shards of gonorrhoea that emerged in baseband and so on going below that then we have device firmware so that's the DSP level some harbour I/O controller so if you've got your hardware I control for USB your homework control public control of the failure of some other device younger GPS chip or whatever else than the other to the firmware level now I guess the problem I've got is that sometimes the to get twisted together so baseband and firmware you in some cases also are year while the iPhone is an update to its baseband you and some of that will have firmware files and that may change the operations of the DSPs all or whatever may be related to the real-time kernel I don't know because I haven't dug into that deep but honestly arm that is the layer and talk about not talk about the operating system that is the actual art radio hardware itself the actual DSPs crunching away now is not unusual arm to update that when you do a softer update only device but the EEOC answer is not unusual as it is unusual sometimes they do it sometimes they don't but the bottom line is that yes they do do it sometimes and sometimes they do put fixes into the DSPs while things if you activity fixes just to get it recertified arm reasonably sure you actually so this is only a thing to software radios were black realises that you think that okay I he is my brand-new iPhone 6s Plus extra bonus whatever our hands – just make a joke about Gaelic Samsung galaxy because were spinning right point in terms of their naming right anyway alright so if I then make a massive change the DSPs and now this things can of neurotransmitter received ever so slightly differently the new you technically may need to requalify that so is the sort of thing that I'd they don't do very often from because they they can't unite but without a whole bunch of other overhead unless is a known issue anyway so arm I was okay yes so why the great things is that… Is remotely upgradable and I'm going on about the ability do this but actually people forget that it was only a couple decades ago that we were stuck with arm app from the knee properly squared proms right where you couldn't remotely was that there was no flash right you couldn't upgrade this things you probably by city Square selectively raise will be molecular electrically erasable ones typically you didn't allegedly raise them on board you would take them out of the socket put them into the program it would apply high-voltage to electrically raise them before we reprogrammed them so you know what the sort of thing that you would just do remotely because because communication wasn't there yes of these things a bit about the field somewhere they be standalone devices there was no Internet of things and therefore all the possible scenarios become possible our end and also we saw were moving towards that was about the late 90s by the early to thousands it was primitive, placed a use arm flash memory to store the firmware and you could then remotely upgrade it with them because of all sorts of other risks being so are and there was not a project I was working on that was this secret squirrel can't seining about ready and we had full right DSP for migraine I was in 2001 2002 so anyway so you've actually played with a bunch of arm software radios and are in kits I think did you say are now I am employed with them myself although the one does a pretty interesting and I kind one order it says it's relatively cheap arm (we're thinking of his mate Michael up experience back in Mario's writers was 2010 I worked for around a company outside Washington DC and needed done software defined radios through the other various thriller agencies in the government and AA help tassels arm now that is critical I was action that the beamforming network team serves an array of evening antennas and did not if you heard no signal whatever band you're interested in it would tell you what direction it was coming from cool service now is critical yes I worked under the beamforming borage notetaking antenna tested run the program then and now running down a small analog signal chain to make sure that all worked in and there was another group that digitised it ran the software defined radio cool so that was cool site just before I jump into the cats arm and amortising about a software defined radio were talking about changing and allowed are what channel you might be iron ore did decoding actual ideology video or whatever it is resending using the radio cracked yes yes yes so you admit it software defined radio replaced essentially the Nawab sign your old analog radial or immuno in certain cases you can use a variable capacitor to change certain performances of the radio were arm or overactive diodes are which can act the capacitor is if you get this injunction theory are hardened that's fine you senior target about me squared proms and of our staff are there true not being hard to change it did – seven and decided capacitor is a total of a screwdriver in that seven further down the technological chain back in time we are so much more flexibility when your digital I absolutely and I'm when you've mentioned before about the capacitor are I was thinking about you that actually would change the local oscillator frequency so that when you were on the TV set what you do is you are dumb have fixed positions of the channels and as you would move the channels that you would have a capacitor behind capacitor arm than air capacitor and as you go from Channel 0 channel one that would change the the capacitance by a linear amount and that then would change the frequency the local oscillator so that would drop down the signal to the same are part of the bandpass filter that then the TV signal got decoded with strip off the carrier and the new start decoding the horizontal and vertical line are information and that would then you change the ray tracing on-screen so yet but then I was there was cool because Andrea Weise there as we used to go and salvage those in the old TV sets and then use them for tuning our antennas so you and don't touch them with your hands otherwise you might go by Katie Hansen imagine that once in an old episode I think I did actually I actually yet little bit of a hole the webbing in my hand that my is all good spine seal nowadays spine totally finally only recounts yeah exactly get to health-related loss that you know hey yes they are so elderly is kits that you are talking about shoreside if you're interested in playing of the software defined radio art as a couple different ways can get started numb and I guess that the basic wanted everyone to roll your own by Dr Ansell project in and of itself, complete with the radial arm there is an article linked to from either the IEEE Spectrum and SNC $40 Yesh software defined radio arm vows of the raspberry pie and therefore are similar stuff which is the 40 hours but the actual radial partners above $40 and it uses a young hat HDTV set HDTV set up from Europe and know there's a certain ship primarily RTL to eat 3 to you and they find out that this chip has a feature wary of you enable it you can spit out the Ra HQ doubter DR IQ modulation out of the rituximab before instead of the demodulated TV stream eyes it's very happy from the article that I read about it and it can transmit but it's pretty low cost arm another option and this is the one I was mentioning that I can wondered by now since it's like $25 eyes from outer fruit and it's just a very basic setup it uses the actually a steamship and it spits out the pain queued out of for you and man if you want to drop some serious money serious being much more than $20-$30 arm there is the hacker Rowse which is stalled by Mike Eisman and John hear more about it is that on a few episodes of the Abdallah podcast by time allowed him get into it since it is project and its $300 you can buy months. Fine and this can transmit and receive any spelling out a known chorus so set of videos available and is website and how to use the hay carafe and if you're lucky enough to go to one security conferences he attends he also teaches two-day seminars as well and software defined radios nice to us so I guess some before we wrap this up is done software radios I guess some the thing that I think is so cool about it is that there was a time not that long ago when everything that we did was channelised everything we did was was selected through you know like your design we design a circuit and it would forever be that circuit you could never modified you couldn't change it remotely can fix problems there was no there was variable software on it and even when the early DDS is came out you know even then the receiver chain was still using dual conversion super heads and yea it was still no it had reached that point where you are able to sample at such high frequency that you actually directly in aid to a DSP process all of this information and decoded however way you would like like decoding the right Q data using an ADC and a DSP was like was unheard of until recently so now all this technology is reach that point where you can have a generic DSP very powerful bit bit of video yes silicon sitting in your device and you can met you can play with it despite by changing software characteristics now changing what what what looks at what what decodes what information and is no change to the circuit board anymore there's nothing to fiddle with there's no lucky say no buttons knobs above all been replaced by the software and then you can build a user interface for it and then you it's like everything this became so much easier and you can just plug it all down have a generic board that does all or a generic shipper does it all in at how a lot of this stuff is possible you say well they're using the like that on the iPhone Apple using either using broad concepts of Qualcomm chips and all that that they they've distilled all this stuff down under these radios have done all that engineering they figured it all out and all the callable problems with him in little little small massive impedances and ducts as between different things of all sort all that out it's all been designed and all you have to do is bring the software and firmware and away you go you got a finished product and that is the one thing that blows me away knowing where we've come from and as the sampling rates get higher and higher and the technologies refined DSPs get more powerful it's going to mean that we can get away with denser pack structures in obvious system and hit the wall at Shannon's limit but in a still arm another topic for another day anyway and in all that but it's going to get better days can get cheap racing faster and are and they can only be a good thing in the end so if you are light load more about it there's plenty of ignition is where you can so did everything else your dad quickly come know that the director pretty nicely alrighty then fair enough what you want to talk more about this you can reach me on Twitter and John Fiji or you can follow our pragmatic show to specifically see show announcements and other related stuff later show remember though that pragmatic is now part of the engineered network it also has an account that engineered_net and has announcements about the whole network and all the shows and you can check them all out are if you like to get in touch with Carmen what's the best way for them to get in touch with him are sure you can reach me on Twitter arm I'll put my candle in the show notes it so that thickly equips it was a while ago started long ago that the pretty much default rate now by branding and everything fits your hassles I still use it are a no-no you can also get a hold of me as well I do another podcast, the engineering comments is also biweekly arm with Jack Shelton and a couple other engineers and generic engineering topics and is a contact form our website are the engineering come and start company can retreat hourly as well) are if you have any smarter feedback about this show all the network then you can use the feedback form an that also we will find a show notes for this episode are also like to take this opportunity to thank our safety and pair in the iOS and shopping for sponsoring the engineered network are as a lot sponsor as well if you're going shopping anyone a great collaborative shopping list at that shopping can help you out and free the first month to check it out at say. SAPI entity – pair is are finally the network also has a patron account arm opening shortly if you'd like if you like what we're doing here the engineered network and you'd like to contribute something anything at all it's very much appreciated and helps out not only to keep existing shows going but it also helps bring new shows to use soap articles of U-boats there so check it out are ill helps thank you so much in advance that and thank you everyone for listening and thank you, thank you John having doing a show of placement�
Duration 1 hour and 23 seconds Direct Download

Show Notes

Miscellaneous Links:

IQ modulation tutorials:

Intro to SDR Kits:

  • Software Defined Radio: $40ish SDR using a hacked European HDTV setup (RTL2832U). The chip has a feature where it can spit out the raw IQ data instead of the specific demodulated TV stream. It’s definitely hacky and it can’t transmit but it’s a relatively low cost intro into SDRs.
  • Adafruit SDR: Basic set-up from Adafruit that’s all contained in one easy USB dongle using the same IC as above.
  • Ossmans Kit: Not exactly a beginner’s kit in the sense that it’s cheap ($300 plus antenna) but probably one of the most full-featured starter’s out there sold by Mike Ossmann. He’s currently got a 9 video course available online to go with the HACK RF.
  • Mike Ossmans Video Course or he also teaches two day seminars on SDRs at security conferences across the globe.

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Carmen Parisi

Carmen Parisi

Carmen is an Electrical Engineer working as an Application Engineer in analogue electronics and has a blog Fake EE Quips that he occasionally posts to. Carmen is also a co-host on The Engineering Commons podcast.

John Chidgey

John Chidgey

John is an Electrical, Instrumentation and Control Systems Engineer, programmer, podcaster and runs TechDistortion and the Engineered Network. John has produced and appeared on many podcasts as well as Pragmatic.

What Happened to Mastodon? You can reach me on the Fediverse as explained here, just search for me on your instance of Mastodon, Misskey or Pleroma and you’ll be able to follow/remote follow me wherever you are!