The World is Your Microphone - EWTS #019

Senan: Hello and welcome to another episode of Enough with the Science.

Joe: Yes, I'm Joe, and in this week's episode we're basically a second-parter; second-parter of a big topic.

Senan: A big topic. I am Senan by the way, and we are on a mission to explore all the wonderful developments in radio technology that made the smartphone in your pocket possible. Last week we spoke about the early history of radio, and we got as far as the ability to send Morse code. There was a thing called a carrier wave, which is just one frequency being transmitted, and it was being turned on and turned off to make a pattern of beeps and dashes and dots and what have you. Somebody understood what that pattern meant and wrote it down as a message.

Joe: I wonder is it different in different languages?

Senan: I assume Morse code is used for more than English, but I couldn't tell you.

Joe: Well, I assume because a dot and a dash stands for one letter, you would imagine.

Senan: Like a handful of dots and dashes for each letter.

Joe: For each letter. And then there's different letters in different alphabets.

Senan: Oh well, I suppose the ones that don't use our traditional kind of... what is the name on it? Roman something alphabet. Anyway, maybe there is other codes for other languages. Obviously there's Chinese characters and there's other languages that don't use the kind of language we have. Good point.

Joe: We come back to that in another episode. [laughter]

Senan: Radio was kind of seen as a bit of a, well a novelty I suppose is a good word for it. The thing that changed that really was the Titanic disaster. The Titanic and some other ships happened to have radio transmitters on them. The Titanic operators were able to send out Morse code signals, and other ships picked them up and came along and helped to rescue some of the survivors.

Joe: For safety purposes, that was why they had radios.

Senan: I would think so.

Joe: Or did they send messages like I need a cheeseburger when I get in? [laughter]

Senan: They could have possibly; a lot of those ocean liners had very rich clients, business people who maybe wanted to send business messages as well, because remember if you're crossing the Atlantic, you're talking about a couple of weeks it was going to take you. The interesting thing about that Titanic disaster is that there was a nearer ship that had a radio, but the radio operator was asleep because he wasn't required; there was no rules there. It was nighttime, so he was reasonably enough having a sleep.

Joe: Finished at five o'clock.

Senan: And didn't hear anything. Had he heard it, that ship could have probably... more people would have survived. That ship would have got there quicker. That was kind of the thing that kickstarted the introduction of laws around radio. It suddenly became a requirement, a legal requirement for ocean-going ships to have radios and they had to have the radio manned around the clock. That was the start of the change in attitude to radio from being a novelty to being something that was actually a tool that was mandatory.

Joe: I'm sure there were military applications as well.

Senan: I have no doubt that the military were probably already experimenting with it even though it was still at the novelty stage. Then of course we had the issue of the fact that Morse code is slow to send. You need people at both ends who actually are skilled, who understand Morse code. Or you can't send a message and you can't interpret it when it comes in.

Joe: They can get the message, but they can't understand it. [laughter]

Senan: That kind of brought a bit of an impetus to try and send voice over radio, which was the next big development after we figured out how to send on a single frequency and use it for Morse code. To understand how voice is sent over radio, you kind of need to understand how voice works with microphones and amplifiers and speakers like a public address system, for example.

Joe: This will be an education for me. [laughter]

Senan: So when I'm speaking to you, my voice is creating pressure waves in the air. It's a smooth transition as my voice rises and falls. Some parts of the air have little pockets of high pressure, other parts have little pockets of low pressure. Those pressure waves are traveling towards you. Or in the case of the microphone, they're traveling towards a little diaphragm, a little disc made of some stiff material. Could be plastic, it could be paper, it could even be a thin sheet of metal. The pressure waves are hitting it and they're making it vibrate in and out. It's vibrating in at the same pattern as the pressure waves that are going through the air from my mouth.

Senan: The back of that disc has a magnet on it. Around that magnet is a coil of wire. It's not stuck to it. There's a gap between the magnet and the coil of wire that's around it. As the disc is shaking in and out because the pressure waves are hitting it, the magnet is moving in and out through the coil. That's the fundamental method that we use for generating electricity. Like any big say a hydroelectric dam for example, which has big turbines. What it is essentially doing is moving magnets past coils of wire and that causes electricity to be generated in the coil of wire.

Senan: Exact same thing is happening in the microphone, except it's a tiny amount of electricity. The pattern of that electricity is what's important. As the magnet that's on the back of the diaphragm is moving in and out in synchronization with the pattern of my voice, it's also generating an electric current in that coil of wire in the same pattern. The pattern of pressure waves that travel through the air to hit the microphone is being replicated as an electrical pattern in the wire in the coil.

Senan: Let's say forget about radio for a minute; we're talking about a public address system. We want that voice to come out of a loudspeaker somewhere. We're talking about a tiny amount of electricity. We need to make it a louder, a bigger, stronger signal before a loudspeaker will be able to make use of it.

Joe: You have to shout. [laughter]

Senan: There's a thing called an amplifier, which is in the electric circuits of the PA system. It just makes everything bigger, stronger. Makes the waves taller. The pattern stays exactly the same. It's the same pattern as came out of my mouth, but it's taller, stronger. Now we can send that to a loudspeaker, which is basically the reverse of a microphone. You've got a cone made of a stiff material. At the back of it there is a magnet. There's a coil of wire around it. Electricity that's coming out of the amplifier goes into the coil of wire and it causes the magnet to move in and out. It forces the magnet to move in and out in the same pattern as the rising and falling current that came from the microphone. That vibrates the loudspeaker and our ears hear that.

Joe: That is kind of amazing in a strange way.

Senan: It is pretty amazing that it can actually replicate the pattern so well that it sounds like a recognizable voice. It sounds almost exactly the same as the person that spoke it. It's incredible really that the fidelity... the accuracy of how that pressure wave in the air can be converted into an electrical pattern which matches it and then can be converted back into a pressure wave again. It's pretty amazing.

Joe: I wonder what the process was of discovering that. They got it to the electricity wave and went ok let's just leave that. Let's just leave it at that. We made electricity. [laughter]

Senan: I'd say what happened was whatever they were feeding that electric wave into was vibrating a little bit. If the room was really quiet, somebody noticed that actually it sounded like a voice. I'd say that's where it started. I could be wrong.

Joe: Let's just invent scientific history. [laughter]

Senan: Okay, now the question is we've now got this electrical current that's rising and falling in the same pattern as the pressure wave that come out of your mouth. The microphone has created this electric current. How do we go about actually transmitting that over radio? Remember our radio transmitter is transmitting on one frequency called a carrier wave. It's doing that because we want other people to be able to transmit at the same time on other frequencies and we don't want to interfere with each other. The carrier wave is a smooth, continuous wave that's the same always. It rises and falls in the same smooth pattern, unlike the electrical wave that the microphone produced, which is continuously changing because our voice is rising and falling, getting higher and lower, louder and softer, and so on.

Senan: How that transmitter works is you have a device called an oscillator in the electronics of the transmitter, and it produces an electric current that is rising and falling at the same frequency that you want to transmit on. The current is going to high volts, then back to zero volts, then down to minus volts, then back to zero volts, then back to high volts, and that's rising and falling at the same rate that we want to transmit whatever frequency we want to transmit at.

Joe: Oscillating if you will.

Senan: Oscillating, yes indeed. That signal goes into an antenna, a wire in the sky. As that electric current...

Joe: Definition of an antenna: A wire in the sky. [laughter] Okay there you go. Connected some way to the ground.

Senan: Connected to the transmitter! Crucially! [laughter] The current from the transmitter, that oscillating current goes into the antenna and the electrons start racing up and down inside in the antenna at the frequency of the oscillator. That produces electric waves that are radio waves that leave the antenna and travel off through the air at that frequency. Somehow, we want to imprint the pattern of our voice into...

Joe: Which is now an electrical pattern.

Senan: Which is now an electrical pattern. There's a really cool thing that happens. If you take two oscillating currents, in other words two electrical currents in wires that are rising and falling in waves, and you bring them together, they'll mix together. You'll end up with a wave which is a mixture of the two of them. It looks probably quite like your original carrier wave, but it has kind of extra bumps in it that match the rising and falling wave of your voice.

Joe: But is this a single wave or is it two...

Senan: The answer to that question is yes and no.[laughter]

Joe: Good! Okay. I love those questions. [laughter]

Senan: For the purposes of us explaining the basics of how it works, we can think of it as a single wave. Later on I'm going to contradict that, but we'll stick with the single wave thing because it acts like it's a single wave anyway. That basically is called modulation. Modulation just means taking the pattern of your voice wave and imprinting it onto the smooth pattern of the carrier wave. Different techniques have been developed for doing that. There's a couple of different ways you can do it.

Senan: The first one and the easiest one to implement in electronics is called amplitude modulation or AM. We've all heard of AM radio.

Joe: Yes, we have. Even me.

Senan: Still quite popular in the US. Not so much on this side of the Atlantic; we've moved nearly everything onto FM. We still have some of the national broadcasters in Europe are broadcasting on long wave or medium wave, that's AM radio. Some of the Asian broadcasters are broadcasting around the world on short wave and the Russians also. That's also AM radio. Short wave, medium wave, long wave, they just refer to different frequencies. It's the same technique regardless of the frequency.

Joe: Okay.

Senan: What basically it does is every radio wave has a height, which is the amplitude is the height of the wave and the higher the wave is, the stronger the power. A transmitter of a thousand watts will make a much higher wave than a transmitter of a hundred watts. How amplitude modulation works is the height of the wave is varied slightly. In other words, it's made a little bit stronger or a little bit weaker to match the pattern of the wave of our voice. That's kind of how we imprint our voice wave onto the carrier wave.

Senan: That means that a loud voice produces a slightly higher wave and a quiet voice produces slightly lower wave. At the other end, the receiver is able to receive that modulated wave and it's able to electronically remove the carrier wave out of it, and it's now left with the original voice wave.

Joe: And that comes through an amplifier and...

Senan: That comes through an amplifier, goes to a speaker. That's what we call demodulation. Modulate on one end and demodulate on the other end.

Joe: I'm following this. I'm delighted with myself.

Senan: I'm going to digress into computers for a sec. Back in the early days of the internet, remember we had to have a dial-up device called a modem.

Joe: No... I do. I do. I do. [laughter]

Senan: It made all that lovely squealing sound when it was starting up at the beginning of the connection. Modem is MO stands for modulate and DEM stands for demodulate.

Joe: Well colour me tickled pink.

Senan: Did you not know that?

Joe: I did not know that.

Senan: Right, there you go.

Joe: And to be quite honest, I was quite happy. [laughter]

Senan: I bet you're happier now! [laughter] Knowledge is good, knowledge is good. Just remind yourself of that Joe. Suddenly now amplitude modulation was born and now people could speak to each other. That made things a bit easier because you didn't need Morse code operators at both ends. Typically you could get the message across a lot faster than you could with Morse code.

Joe: And you could shout at people, which is always good. Very difficult to shout at people in Morse code.

Senan: However, it has some problems. Amplitude modulation is very susceptible to interference. There's lots of radio waves bouncing around in the atmosphere and they're interfering with each other. There are electrical devices producing bursts of radio frequency and so on. There's all kinds of interference floating around. Generally that interference affects the strength of the wave you're listening to, of the frequency you're listening to. It might make it stronger or it might make it weaker. Because we're using those varying strength of the wave to carry our voice, that interferes with the method we're using; the amplitude modulation we're using to carry our voice. So interference typically on AM radio makes it sound crappy.

Joe: Okay.

Senan: Quality is definitely a problem. If you listen to a short wave radio station from China or somewhere, I mean you can barely hear it because the interference is so bad.

Joe: Why are you listening to short wave radio stations from China?

Senan: This is a conversation for later. [laughter] I have to plead the Fifth Amendment even though I'm not American, because I might incriminate myself. Anyway, to solve that problem along came something called frequency modulation, or FM radio. Most of us are familiar with the idea that FM radio sounds a hell of a lot better than the old medium wave or long wave, which was AM.

Senan: What's happening here is instead of the amplitude, the height, the strength of the wave being varied with our voice, the frequency is being varied a little bit instead. If the carrier wave is running at a thousand kilohertz for example, if we speak softly then the carrier might be at 996 kilohertz. If we speak loudly, it might be at 1004 kilohertz. We're slightly changing the frequency all the time to match the pattern of the voice wave that's being imprinted onto the carrier wave. The great thing about FM is that it is more or less immune to interference until the interference is really bad.

Senan: The signal comes through really well, we can get lovely stereo sounding music, and unless there's a lot of interference, it just sounds perfect. Essentially FM receivers are ignoring most of the interference. They can do that because of the way FM works. FM is used so for example apart from us listening to music on the radio, a lot of aircraft communication, a lot of marine ships use FM as well because of the clarity of it.

Joe: Would they use FM short or long wave?

Senan: There are different bands used. The long distance ships and planes communication is over a kind of AM called SSB, which we'll come to in a minute. Short range... the interesting thing about FM, it generally is used on the higher frequencies VHF and UHF and those frequencies only travel line of sight. They offer high quality communication, but only over line of sight. Ships and planes that are near the coast or near to an airport will use FM.

Joe: Switch over.

Senan: They use the higher frequency bands when they're near shore, and then the lower ones which are more suitable for AM when they're further away. We talk about that thing I mentioned a go, SSB. It stands for single sideband. Now this is where I get to contradict where I said earlier you asked me was it one wave or two waves that get sent.

Joe: I was waiting for this. The highlight of the show.

Senan: One wave! [laughter] Actually, some years after we started using AM, we had better equipment that allowed us to analyse that radio signal in detail, and we discovered really there was three components to it. Kind of three separate waves that are interlinked. It's possible to just take away two of those components and just send one of the three, and you can still get your signal through. The benefit of doing that is that instead of your transmitter power being divided up between three separate components, you're now putting all your power into one of those three components. You're ignoring the other two. Your signal for the same amount of power goes much further.

Joe: But is the quality the same?

Senan: It is a little weird. It sounds... it is perfectly understandable...

Joe: It comes out as gobbledygook. No one can understand a word. But it's great cause you can send it further. You can send gobbledygook further with it. We'll call it the rubbish cannon. [laughter]

Senan: No, it is perfectly intelligible. It just sounds a little bit weird. The voice sounds a small bit weird.

Joe: I think that was a review for this podcast. [laughter]

Senan: If only we had... we were so short of reviews I'd happily take that one. [laughter] The other thing is that tuning in an SSB, it stands for Single sideband. Basically the three components are the main carrier wave and two sidebands.

Joe: Yes.

Senan: You're getting rid of the carrier and one of the sidebands and you're left with a single sideband, which can either be the upper band or the lower band.

Joe: That's kind of weird though, isn't it? When you think they wanted to... just got rid of the sidebands?

Senan: Because that's actually where the information is carried.

Joe: Ah, okay.

Senan: If you send the carrier on its own without the sidebands, you're not sending anything other than beeeeep.

Joe: Okay. Here we go.

Senan: It's weird. In order for this to work, the receiver can't decode the incoming signal without the carrier wave, even though we've deliberately not sent the carrier wave. The thing is, the receiver knows what the carrier wave is supposed to be. It knows what frequency the carrier wave is supposed to be. So it generates an artificial one and mixes it with the incoming signal and that allows it to decode the signal.

Joe: Ouch.

Senan: It essentially made long distance... so SSB, any of the long distance radio communications going on with planes or ships or amateur radio ham operators, they are all using SSB because it's so economical power wise. If you've got to go a long distance with a relatively small amount of power. It's not used at all for broadcast because, as I said, the voice sounds a bit weird, and tuning it is a little bit more technical than an ordinary radio. So it's only used for actual two-way communication.

Senan: Yeah, so once voice became a thing, that suddenly...

Senan: Voice over radio, I mean, of course. Not voice between monkeys. [laughter]

Joe: Yes. Okay.

Senan: That opened up the door to broadcasting, to commercial radio stations. I mean nobody was going to listen to a Morse code radio station unless they were majorly down the nerd rabbit hole, which I'm sure nobody in this room is.

Joe: We'll come back to that. Let's come back to that. [laughter]

Senan: The first two stations we believe that were commercial broadcasters were KDKA in Pittsburgh, USA, and PCGG in Rotterdam in the Netherlands. However, before the vast majority of the population could receive those stations, they needed easy to operate and reliable receivers. The receivers of the time were quite technical. The tuning, there was maybe half a dozen tuning knobs that you had to fiddle with to tune into your station.

Joe: Kind of what came first. People have radios first and then they had the stations or did they have stations broadcasting to nobody?

Senan: I would say the stations were broadcasting to more or less nobody other than a handful of enthusiasts who probably knew all the people in the station. I suppose maybe they advertised in newspapers and it caught on bit by bit. The receivers were not very friendly to people who didn't understand the technicalities of radio. They were also not that reliable in terms of a particular receiver might work well on one frequency but work really poorly on another frequency. If you wanted to listen to lots of different radio stations, which admittedly there weren't that many at the time...

Joe: You were lucky if you found one. What the hell is this? [laughter] I imagine selling a receiver that could only pick up one station, I'm sure somebody would want it.

Senan: You'd want to like the station. Yeah, certainly would. Anyway, along came a guy called Edwin Armstrong who made a brilliant invention called the Superheterodyne receiver.

Joe: You were just waiting, you were just waiting to say that since the beginning of this podcast.

Senan: Well I've been practicing how to say it without stumbling over it for weeks.

Joe: So did he invent the Heterodyne receiver and then it just got really good after like the first several iterations?

Senan: He probably stole the idea from somewhere and said I'll stick 'super' in front of it to make it seem like I made it better.

Joe: Well it sells, super sells.

Senan: Super, super sells. It made receivers much easier for the general public to use. One tuning knob instead of a pile of them. It was much more reliable in terms of it could tune into a huge range of different frequencies and all of them worked well. It was stable; once you tuned it into a frequency it stayed on that frequency unlike some of the older ones which drifted around and you had to start fiddling with them again to get the signal back. It just made them much easier for the general public to use and suddenly they became popular because people wanted to listen to commercial radio. They wanted to hear the news, which before that the news they got out of the newspaper might have been a week out of date whereas with the radio station they were able to get right up to date news.

Joe: So who was the first radio broadcast?

Senan: As I said KDKA in Pittsburgh and PCGG in Rotterdam.

Joe: But the actual first voice...

Senan: Oh the person, I've no idea. No idea. It wasn't me. Should have been us, but it wasn't.

Joe: Let me fix that vast gaping hole in your knowledge by just typing it into Google. Reginald Fessenden, 1906, from Brant Rock, Massachusetts, there you go. And featuring a violin solo and a Bible reading.

Senan: Well, I'm glad they got their priorities right. The music came first.

Joe: Absolutely. Well, I don't know it didn't give me the order what they did.

Senan: The interesting thing about the Superheterodyne receivers, that technique...

Joe: How many times are you going to try and get that word into this podcast? [laughter]

Senan: Superheterodyne, I really like that word! That same technique is still used in almost all radio receivers to this day.

Joe: That is kind of very interesting.

Senan: He really was on to something. He was a very smart guy, this Armstrong guy, because he also invented FM radio. He got mired in years of...

Joe: And then he was on the moon as well wasn't he?

Senan: No, I think that was his nephew Neil.

Senan: The unfortunate gentleman spent years in patent battles over the things he had invented. People were stealing his ideas and he was in and out of court. Eventually he actually died tragically by suicide in 1954. So a very brilliant man who came to a very difficult end.

Joe: Oh God. And when was this Superheterodyne?

Senan: Superheterodyne was in the twenties I think.

Joe: Wow. 35 years trying to...

Senan: Internally what it did, it simplified... radio frequencies are quite high and it's difficult to make electronics that work reliably at those high frequencies, especially we're talking about the fledgling early days of electronics here. What his great breakthrough was that he shifted the frequency of the incoming radio signal down to a much lower, what's called intermediate frequency. The electronics in the radio could work much more reliably with that.

Joe: So in the radio it changed the frequency.

Senan: In the radio after it was received, it shifted it down internally to a lower frequency. Still not a frequency you can hear. Our audible frequencies are actually much lower again, but it was like a halfway between the incoming radio signal and the eventual audio that would come out of the speaker. The key thing about it was that that intermediate frequency, the electronics were much simpler. He could make simpler, more reliable, more sensitive electronics that worked properly with the intermediate frequency. That was the key innovation that he brought there.

Senan: I'm going to digress briefly. We're going to go on. We're nearly at the end of... believe it or not this is going to be our first triple-parter.

Joe: Right. Okay. That's news to me.

Senan: This is part two. But we're only crawling through the material. We're going to get...

Joe: We're going to get to the mobile phone eventually. This is where we're heading the next episode.

Senan: We're heading towards the mobile phone but look we need to pay proper homage to all these wonderful developments that happened. I'm going to briefly digress into amateur radio. For about the last hundred years the amateur radio movement has been a strong thing around the world. Enthusiasts who are into technology, far more into it than you and I are, wanted to experiment.

Joe: Now you're kind of a bit of an... let's put cards on the table here. You're a bit of an enthusiast.

Senan: I'm a bit of an enthusiast yeah. But these guys were serious. They actually wanted to figure out how this technology worked. Guys were building their own radio transmitters in their sheds back a hundred years ago. These guys were just willing to get stuck in and see what they could do.

Senan: It was only after the Titanic disaster that the radio spectrum got regulated. In other words, certain bands, certain chunks of the radio spectrum frequencies were allocated to certain things. Ships got a certain amount, the military got a certain amount, the police got a certain amount, and so on. The regulators, the people who drafted the regulations, as far as they were concerned the amateurs, the ham radio people were just a nuisance. There was this set of frequencies called short wave that nobody thought was useful, thought it was completely useless. Can't be used for any serious purpose; we'll let the amateurs have that. Of course, the amateurs proved that you could use short wave to talk to other people on the other side of the world. The irony it was funny how they got a hold of something that was perceived to be worthless and was anything but worthless.

Senan: But a precedent was set. It meant that certain bands were set aside for amateurs and that precedent still exists today. There are about a dozen different bands. A band is like a block of frequencies. There are about a dozen bands still reserved for amateur use to this day and they're in use continuously. There's hundreds of amateurs, thousands around the world chatting to each other every day, if you tune into those bands.

Joe: That just scares me slightly that you would do that. I just want to hear somebody's conversation. Somebody in America is talking to some randomer in Australia. I'm just going to tune in for an hour and see what they're talking about.

Senan: They're all keenly aware of the fact that anybody can hear their stuff so it's not like that you're eavesdropping on something that somebody thinks is private.

Joe: I imagine some of their discoveries have sort of influenced the direction of...

Senan: Oh absolutely. A lot of them have pushed the boundaries of what's possible with the technology. With relatively small amounts of power. Most of them are operating at like maybe 100 watts or even less in some cases. In terms of radio that's a very small amount of transmit power. The commercial radio stations are using thousands of watts. Yet these guys have figured out how to make those weak signals go around the world and be picked up by their peers across the other side of the planet. They have pushed the boundaries and a lot of the things they have discovered have found their way back into commercial radio afterwards.

Senan: Also, they're not just weird cranks. They are also considered to be the last resort in the case of a major disaster for communications.

Joe: Okay. [laughter] This would be funny if it wasn't so pressingly real.

Senan: I mean there are things happening in the world right now that make us think about the potential for World War Three and disasters like that. The thing is, these days most of our global communication around the world relies on the internet. The internet is a complicated network. If you send a message to your friend in Australia from here over the internet it goes through a lot of different devices to get there. There's a lot of links in the chain and if one of those links is gone, the chain is gone. The internet is fragile. If a large-scale catastrophe happens, the internet is fragile. Ham radio is very resilient because there's nothing...

Joe: Great. Because there's nothing I will want to do more at the end of the world is to talk to some man in a basement in Utah about the coming of the end of the world. [laughter]

Senan: You know, there's just no talking to you. [laughter] Here I am espousing the benefits of these people who have spent their entire lives learning how to use this technology. Anyway the point is that all you've got is a transmitter and a receiver so there's nothing in between, there's no chain in between to be broken. As long as the transmitter and the receiver are working, that message will get through. We may end up relying on those people that you're sniggering about over there.

Joe: Oh my God. Part of me was with the whole internet not working, I was like well I wonder what that'd be like, but then I realised maybe that wouldn't be so good. You wouldn't be able to get your pictures of cats.

Senan: Wouldn't get the pictures of cats and tricycles. Our podcast would be kind of at an end. It would just be two old guys talking to each other in a room.

Joe: Well... [laughter]

Senan: Anyway, that is the story of how voice found its way onto radio. We've kind of run out of time for this week's episode so in the next episode part three, our first three-parter, hopefully won't turn into a four-parter.

Joe: It's going to be a three-parter. If I have to shoot you before the end of it. [laughter]

Senan: Anyway we are going to start talking about some of the technology advancements that have occurred that have found their way into your mobile phone.

Joe: It's all leading towards the mobile phone.

Senan: It's all leading towards all the different technologies that came together to make your phone possible and reliable. We're going to be talking about transistors, software-defined radio, digital modulation, encryption, packing more data into less bandwidth, etc, etc. We have a lot to talk about next week.

Joe: Maybe we shouldn't be that detailed in what's coming up in the next episode. Maybe we should leave some juicy tidbits just so they discover themselves.

Senan: For people a surprise. Absolutely. But the story won't make sense if we leave some links out of the chain.

Joe: Okay. I'll go with that.

Senan: Anyway look, I think we've gone far enough this week and this is Senan signing off here for this week's episode. I hope you have a nice weekend.

Joe: Okay, thanks for listening.