WEBVTT - Frequency Hopping 0:00:04.120 --> 0:00:07.160 Get in touch with technology with tech Stuff from how 0:00:07.200 --> 0:00:13.680 stuff works dot com. Hey there, and welcome to tech Stuff. 0:00:13.720 --> 0:00:16.640 I'm your host, Jonathan Strickland. I'm an executive producer at 0:00:16.640 --> 0:00:19.720 how Stuff Works and I love all things tech and 0:00:19.760 --> 0:00:22.880 in our last episode, I talked about actress Hetty Lamar 0:00:22.920 --> 0:00:25.480 and how she came to America just before World War 0:00:25.560 --> 0:00:28.280 Two erupted in Europe and how she co invented a 0:00:28.360 --> 0:00:33.280 form of secret communication via radio signals with composer George Antile. 0:00:33.840 --> 0:00:37.800 These two seemingly unlikely inventors proposed a method in which 0:00:37.840 --> 0:00:41.080 allied radio operators would be able to control something like 0:00:41.159 --> 0:00:44.519 a torpedo using radio signals without fear of having their 0:00:44.560 --> 0:00:48.880 operations jammed by enemy operators. The system made clever use 0:00:48.880 --> 0:00:51.879 of the same basic technology that player Pianos used, and 0:00:51.880 --> 0:00:54.000 if you haven't heard that episode, I urge you to 0:00:54.080 --> 0:00:56.720 check it out as it's a good starter for today's 0:00:56.840 --> 0:01:00.440 show and just a quick reminder. The system that Lamar 0:01:00.520 --> 0:01:03.480 and and Tile proposed would allow a radio transmitter and 0:01:03.520 --> 0:01:07.679 a paired receiver switch radio frequencies multiple times during a 0:01:07.720 --> 0:01:11.720 transmission in an effort to avoid frequency jamming. The trick 0:01:11.840 --> 0:01:14.840 was to create a system where the transmission antenna and 0:01:14.880 --> 0:01:19.000 the receiver could automatically tune to the appropriate frequencies on 0:01:19.040 --> 0:01:21.720 their own in such a way as to be unpredictable 0:01:21.840 --> 0:01:24.800 to enemies. To do that, you would need some sort 0:01:24.800 --> 0:01:28.399 of instructions that both systems could carry out in synchronization, 0:01:28.920 --> 0:01:31.720 and Tile supplied this mechanism in the form of paper 0:01:31.840 --> 0:01:35.679 rolls identical to the type used in player pianos, complete 0:01:35.680 --> 0:01:38.800 with the ability to tune into eighty eight different frequencies, 0:01:39.120 --> 0:01:43.240 just as a typical piano has eight keys. So Hetty 0:01:43.319 --> 0:01:46.440 Lamar and George Antile submitted their idea to the United 0:01:46.440 --> 0:01:52.760 States Navy. The Navy's response was less than enthusiastic. Essentially, 0:01:52.800 --> 0:01:55.640 the Navy said, we don't want to put player pianos 0:01:55.640 --> 0:01:59.160 in torpedoes, which seems like a pretty short sighted counterpoint. 0:01:59.720 --> 0:02:03.400 In a ddition, some modern historians have trouble believing Henny 0:02:03.480 --> 0:02:06.560 Lamar could have come up with this idea herself. Some 0:02:06.720 --> 0:02:10.400 have suggested that rather than invent the approach, she simply 0:02:10.480 --> 0:02:13.040 learned about it while she was still in Austria, while 0:02:13.080 --> 0:02:17.040 she was married to Fritz Mandel, and armament manufacturer who 0:02:17.120 --> 0:02:20.320 was supplying weapons to the Nazis, but according to a 0:02:20.440 --> 0:02:24.880 nine interview with Lamar, that simply wasn't true. She said 0:02:24.919 --> 0:02:27.880 she never learned anything about armaments from her husband, who 0:02:27.880 --> 0:02:31.720 preferred to keep his wife in relative seclusion. Personally, I 0:02:31.760 --> 0:02:35.000 think it is completely believable that Lamar came up with 0:02:35.040 --> 0:02:38.519 this idea, as she understood the potential that frequency hopping 0:02:38.520 --> 0:02:42.080 could provide for secret communications, but she lacked the mechanical 0:02:42.120 --> 0:02:45.480 and electrical engineering knowledge to make practical use of it, So, 0:02:45.520 --> 0:02:47.560 in other words, it's not like she came out of 0:02:47.600 --> 0:02:51.400 nowhere with a fully formed implementation of her idea. The 0:02:51.440 --> 0:02:54.680 military told Lamar that if she wanted to support the 0:02:54.760 --> 0:02:58.960 United States during the war, she should stop coming up 0:02:58.960 --> 0:03:02.240 with ideas and instead she should put her fame to 0:03:02.400 --> 0:03:06.680 use in selling war bonds. Lamar, believing the United States 0:03:06.760 --> 0:03:09.200 to be on the right side of the conflict, did 0:03:09.240 --> 0:03:14.280 just that. Her idea languished with other classified documents locked 0:03:14.320 --> 0:03:18.880 away in the United States Navy, and the reason that 0:03:18.960 --> 0:03:21.639 it was locked away was that while the Navy didn't 0:03:21.639 --> 0:03:25.160 plan on using it, they were concerned that some of 0:03:25.200 --> 0:03:29.960 this information could potentially give the enemy valuable information if it, 0:03:30.040 --> 0:03:33.000 in fact we're shared publicly, so it got put into 0:03:33.200 --> 0:03:36.920 secret storage. Essentially, she went on to perform for troops 0:03:37.000 --> 0:03:39.480 and raise money for the United States, reportedly raising the 0:03:39.520 --> 0:03:43.240 equivalent of more than twenty million dollars by some estimates. 0:03:44.040 --> 0:03:46.960 This was all before she herself was a citizen in 0:03:47.000 --> 0:03:49.440 the United States. She was not yet a cisen but 0:03:49.520 --> 0:03:53.240 she was raising money for the US. In two the 0:03:53.280 --> 0:03:56.560 United States government, in an act I can only describe 0:03:56.800 --> 0:04:03.240 as wicked, seized Lamar's patents and labeled her an enemy alien. 0:04:04.000 --> 0:04:08.160 Lamar was perplexed here. She had been participating in events 0:04:08.440 --> 0:04:11.760 to raise money for the United States, she had willingly 0:04:12.040 --> 0:04:15.360 submitted her patent to the United States military, and now 0:04:15.400 --> 0:04:18.640 she found herself labeled by that same government as an 0:04:18.680 --> 0:04:22.640 alien resident from a hostile country because she was originally 0:04:22.680 --> 0:04:26.679 from Austria. It was a pretty big insult on top 0:04:26.839 --> 0:04:30.880 of everything else. But Lamar kept on working in Hollywood. 0:04:31.200 --> 0:04:33.719 She produced her own film at a point when such 0:04:33.720 --> 0:04:36.520 a thing was unheard of. The studios didn't care for 0:04:36.520 --> 0:04:39.320 that one bit, as they had a pretty tight stranglehold 0:04:39.360 --> 0:04:43.360 on entertainment at the time, and no studio wanted actors 0:04:43.400 --> 0:04:46.480 to get big ideas about producing their own movies independently. 0:04:47.000 --> 0:04:50.880 The studios liked it, with the actors being entirely dependent 0:04:50.960 --> 0:04:53.520 upon the studio, so this was not something that was 0:04:53.560 --> 0:04:58.160 greeted with acclaim among studio executives at the time. She 0:04:58.240 --> 0:05:00.320 was able to bring her mother over to the States. 0:05:00.360 --> 0:05:03.160 If you remember, in the last episode, she was concerned 0:05:03.160 --> 0:05:07.080 her mom had fled Austria to England but had been 0:05:07.120 --> 0:05:10.160 stuck there for a while. But Hetty Lamar was able 0:05:10.200 --> 0:05:13.200 to get her mom to over to the United States, 0:05:13.400 --> 0:05:15.919 and she made a good deal of money when she 0:05:15.960 --> 0:05:20.039 started cecil b Demills, Samson and Delilah, but she would 0:05:20.400 --> 0:05:22.720 end up losing a lot of that money producing her 0:05:22.720 --> 0:05:26.520 own movies, which would be commercially unsuccessful. She was attempting 0:05:26.560 --> 0:05:29.720 to create roles for herself because she was frustrated that 0:05:29.839 --> 0:05:32.800 studios were giving her the same sort of roles over 0:05:32.839 --> 0:05:36.799 and over, which were essentially wicked temptresses, and she wanted 0:05:36.800 --> 0:05:40.360 to play different types of parts. So she made her 0:05:40.360 --> 0:05:44.239 own movies, but they ended up not doing so well 0:05:44.480 --> 0:05:49.000 and it almost bankrupted her. In nineteen Lamar would ask 0:05:49.040 --> 0:05:50.640 a friend of hers who was in the U. S. 0:05:50.720 --> 0:05:53.719 Navy if he might be able to find out whatever 0:05:53.800 --> 0:05:57.280 happened to her patent because it got locked away in secrecy, 0:05:57.279 --> 0:05:59.320 and she was just curious, you know, whatever happened to 0:05:59.360 --> 0:06:02.440 that idea. I came up with her friend did some 0:06:02.520 --> 0:06:05.880 digging and discovered that the technology she and Antile had 0:06:05.880 --> 0:06:09.520 proposed in ninety one was now in common use in 0:06:09.560 --> 0:06:13.440 the United States military for secret communications. Her patent at 0:06:13.480 --> 0:06:17.679 that point had expired. So patents provide protection, but only 0:06:17.760 --> 0:06:19.920 for a set number of years. So if you have 0:06:20.040 --> 0:06:23.680 an invention and you patent it for the amount of 0:06:23.720 --> 0:06:26.680 time that the patent is active, you have protection. If 0:06:26.680 --> 0:06:31.000 someone else uses your invention, creates something that relies upon 0:06:31.040 --> 0:06:35.320 your invention without first licensing that from you, without you 0:06:35.400 --> 0:06:38.839 giving them permission to do it, you can, uh you 0:06:38.839 --> 0:06:41.120 can pursue a legal case against them and say that 0:06:41.160 --> 0:06:45.120 they've infringed upon your patented idea or your patented invention, 0:06:45.279 --> 0:06:47.880 I should say, and if the court finds it is so, 0:06:48.360 --> 0:06:53.120 you could be awarded money for that. However, patents only 0:06:53.480 --> 0:06:55.560 are good for a certain number of years, and after 0:06:55.640 --> 0:06:59.120 that they passed into the public domain, which is meant 0:06:59.200 --> 0:07:03.640 to give inventors the opportunity to take advantage of previous 0:07:03.680 --> 0:07:07.320 inventions and then improve upon them. Otherwise, you would lock 0:07:07.400 --> 0:07:10.280 an ideal way and it would become the exclusive domain 0:07:10.480 --> 0:07:15.080 of a single party, and that would squelch innovation. Well, 0:07:15.560 --> 0:07:19.239 Lamar's patent had entered into the public domain by nineteen 0:07:19.360 --> 0:07:23.280 sixty nine. However, as it turns out, the military had 0:07:23.320 --> 0:07:28.720 been using that patented idea since before the patent had 0:07:28.760 --> 0:07:33.440 actually expired, and that meant that Lamar should have been 0:07:33.480 --> 0:07:36.760 paid for the use of that idea. As those who 0:07:36.840 --> 0:07:41.040 submitted their inventions to the Inventor's Counsel I mentioned them 0:07:41.040 --> 0:07:44.120 in the last episode, they were supposed to receive compensation 0:07:44.360 --> 0:07:48.640 if those inventions were actually put into practice. Lamar was 0:07:48.880 --> 0:07:51.680 unaware of the fact that they had been doing this 0:07:52.000 --> 0:07:54.520 by the time she found out her patent had expired, 0:07:54.880 --> 0:07:57.520 and she did not know that if she were to 0:07:58.160 --> 0:08:02.600 sue within six years of the patent expiring for revenue 0:08:02.800 --> 0:08:05.280 that should have been hers, she could have won the 0:08:05.360 --> 0:08:08.400 court case. She was unaware of all of that, and 0:08:08.560 --> 0:08:12.400 as a result, she did not receive any money from 0:08:12.520 --> 0:08:16.440 her patented idea that the United States government was actively 0:08:17.640 --> 0:08:23.040 exploiting from the nineteen fifties onward. The implementation in uh 0:08:23.080 --> 0:08:26.320 in question the one that was first used back when 0:08:26.360 --> 0:08:30.600 her patented idea was still patented, was called the Sanna 0:08:30.680 --> 0:08:34.720 buoy or Sanna boy as most people pronounce it, But 0:08:34.800 --> 0:08:39.120 it's a a portmanteau of sonar and buoy or boy 0:08:39.840 --> 0:08:42.200 I say, booie. That's just the way I've always said 0:08:42.240 --> 0:08:45.240 that word. But you know, thing thing what floats in 0:08:45.280 --> 0:08:49.080 the water SnO. Sano buoys have been around for a while, 0:08:49.120 --> 0:08:52.960 but this particular implementation used Lamar's proposal of frequency hopping, 0:08:53.480 --> 0:08:55.760 and it would allow a buoy in the water to 0:08:56.520 --> 0:08:59.880 send sonar signals out in an attempt to detect in 0:09:00.400 --> 0:09:03.680 submarines in the area and send those communications up to 0:09:04.160 --> 0:09:08.480 an airplane that's flying surveillance overhead. So you would actually 0:09:08.480 --> 0:09:13.000 deploy several of these Sauna buys in an area, and 0:09:13.080 --> 0:09:15.720 you would use any signals they were picking up to 0:09:15.800 --> 0:09:19.640 triangulate the position of an submarine and be able to 0:09:20.679 --> 0:09:23.480 locate them and then track them. So, in order to 0:09:23.559 --> 0:09:27.080 do that effectively, you want that communication to be secret 0:09:27.360 --> 0:09:30.720 and you want you want to avoid the potential of 0:09:31.040 --> 0:09:34.520 whoever you're trying to spy on be able to jam 0:09:34.559 --> 0:09:37.240 the signals, so you need some way of preventing that. 0:09:37.360 --> 0:09:40.640 Frequency hopping was the way her patent had passed to 0:09:40.679 --> 0:09:43.560 a contractor who was working on the Sauna Buy. His 0:09:43.679 --> 0:09:49.920 name was rummeld Ireneus Sabor Machaki, and I know I've 0:09:50.080 --> 0:09:52.680 butcher trying to pronounce that name. It was a heck 0:09:52.679 --> 0:09:55.120 of a name to try and pronounce. He said that 0:09:55.160 --> 0:09:58.480 when he was handed the patent the names had been expunged. 0:09:58.640 --> 0:10:00.680 He didn't know who was respond stable for it. It 0:10:00.760 --> 0:10:03.720 was just property of the United States Navy. But he 0:10:03.840 --> 0:10:06.120 used it as a basis for his design of a 0:10:06.240 --> 0:10:10.800 frequency hopping communication system between the Sauna Buy and airplanes, 0:10:11.040 --> 0:10:14.160 though his version used a computer chip to determine which 0:10:14.200 --> 0:10:17.719 frequencies the two elements would use in sequence rather than 0:10:17.880 --> 0:10:21.880 rolls of piano paper, so they upgraded the means of 0:10:21.960 --> 0:10:25.720 sending the series of frequencies, but it was still the 0:10:25.760 --> 0:10:29.240 same idea. Years later he discovered who had written the patent, 0:10:29.720 --> 0:10:32.520 and he created a page on his personal website that 0:10:32.559 --> 0:10:36.319 he titled a Tribute to Hetty Lamar. He detailed how 0:10:36.360 --> 0:10:39.120 the frequency hopping technology was used not just in Saanna 0:10:39.160 --> 0:10:43.280 Buy's but also early surveillance drones developed by the Aerojet 0:10:43.320 --> 0:10:47.800 General Corporation and which eventually were used in Vietnam. In 0:10:47.880 --> 0:10:51.439 his piece, he thanked heavy Lamar for contributions, and as 0:10:51.480 --> 0:10:54.840 the years went by, Lamar hit many obstacles. She would 0:10:54.840 --> 0:10:57.559 be married several times, but the marriages would never last 0:10:57.679 --> 0:11:00.240 very long. She had two children of her own and 0:11:00.280 --> 0:11:03.679 adopted another, though her adopted son would essentially be raised 0:11:03.679 --> 0:11:06.440 by another family. She would be taken under the care 0:11:06.480 --> 0:11:09.640 of a doctor named Max Jacobsen, sometimes referred to as 0:11:09.720 --> 0:11:13.760 doctor field Good, who got her hooked on amphetamines. His 0:11:13.880 --> 0:11:16.720 medical license would ultimately be revoked by the New York 0:11:16.760 --> 0:11:20.200 State Board of Regents in nineteen seventy five, and Hey 0:11:20.280 --> 0:11:24.600 Lamar would become a recluse. She had multiple plastic surgeries, 0:11:24.720 --> 0:11:27.520 some of which did not go well, which made her 0:11:27.559 --> 0:11:31.280 withdraw even further. She was ashamed of her appearance, and 0:11:31.360 --> 0:11:35.280 when she was contacted in nineteen seven and told that 0:11:35.400 --> 0:11:38.360 lockeed Martin and the military plan to honor her with 0:11:38.400 --> 0:11:42.320 an award for her contributions for her creation of frequency hopping, 0:11:42.640 --> 0:11:47.560 her response was, well, it's about time. She did not 0:11:47.640 --> 0:11:50.959 attend the ceremony herself. She was self conscious about how 0:11:51.000 --> 0:11:54.280 she looked, but her son accepted the award for her, 0:11:54.480 --> 0:11:56.120 and she called him right in the middle of the 0:11:56.160 --> 0:11:59.240 acceptance speech, to the great amusement of both her son 0:11:59.440 --> 0:12:03.079 and the crowd. Old Hetty Lamar died in two thousand, 0:12:03.400 --> 0:12:05.880 at the age of eighty five, and by then her 0:12:05.960 --> 0:12:08.840 story had been told a few times, but her name 0:12:08.920 --> 0:12:13.160 and performances had often been used as punchlines. Ultimately, I'm 0:12:13.240 --> 0:12:16.559 very sad for Hetty Lamar, as I feel her contributions 0:12:16.559 --> 0:12:22.959 were criminally underappreciated and unrewarded and unacknowledged, and the things 0:12:23.000 --> 0:12:24.920 that she was most known for were things that she 0:12:25.080 --> 0:12:29.520 ultimately thought were not very important, playing these roles that 0:12:29.600 --> 0:12:32.480 the studio kept pushing on her, not the parts that 0:12:32.520 --> 0:12:38.440 she wanted, nor her intellectual contributions. Those were left in 0:12:38.840 --> 0:12:45.960 complete ignorance among most people, and I find that really tragic. However, 0:12:46.000 --> 0:12:48.000 when we come back, I'm going to talk more about 0:12:48.080 --> 0:12:51.200 frequency hopping and how it's an underlying technology for a 0:12:51.240 --> 0:12:54.280 lot of the stuff we use today. But first let's 0:12:54.320 --> 0:13:04.280 take a quick break to thank our sponsor. So the 0:13:04.360 --> 0:13:08.080 concept behind frequency hopping is simple. You have two or 0:13:08.080 --> 0:13:11.480 more radios tuned to a frequency which allows for communication 0:13:11.559 --> 0:13:15.680 between those two radios, and in synchronized moments, you switch 0:13:15.840 --> 0:13:20.080 the transmitting and receiving frequencies to a different frequency but 0:13:21.040 --> 0:13:22.960 different from the one they had been using, but the 0:13:23.040 --> 0:13:26.920 same as each other, So they both simultaneously switched to 0:13:26.960 --> 0:13:30.600 a new frequency, the same new frequency. Doing this prevents 0:13:30.679 --> 0:13:33.520 someone else from easily being able to snoop on you, 0:13:33.760 --> 0:13:37.679 or to jam your conversation, or just to encounter interference 0:13:37.679 --> 0:13:40.400 in general, because you're never on any one frequency for 0:13:40.480 --> 0:13:43.400 two terribly long. So imagine you're listening to a song 0:13:43.520 --> 0:13:45.880 on the radio, and a minute into the song, your 0:13:45.960 --> 0:13:49.920 radio switches spontaneously to a different station, but the same 0:13:49.960 --> 0:13:51.800 song is on there, and it's playing in the exact 0:13:51.800 --> 0:13:54.400 same spot, And you find out that your radio and 0:13:54.440 --> 0:13:58.000 the transmitter are synchronized, and that if you had stuck 0:13:58.080 --> 0:14:01.560 to your original station, you'd only hear part of the 0:14:01.600 --> 0:14:03.720 song before the signal just went away and you were 0:14:03.760 --> 0:14:06.920 listening to nothing at all. That's the basic idea. It's 0:14:06.960 --> 0:14:09.480 simple in concept, but how do you implement it so 0:14:09.520 --> 0:14:13.080 that it actually works. Both the transmitter and the receiver 0:14:13.320 --> 0:14:17.760 rely upon a pseudo random sequence to determine the series 0:14:17.800 --> 0:14:21.200 of frequencies that are to be used throughout the communication, 0:14:21.600 --> 0:14:24.640 and pseudo random kind of means what it sounds like 0:14:24.920 --> 0:14:29.680 it's a process that on casual glance looks like it's random, 0:14:29.960 --> 0:14:33.280 but in reality it isn't. I've talked about this in 0:14:33.440 --> 0:14:37.280 previous episodes of tech Stuff. Computers can create things that 0:14:37.360 --> 0:14:39.720 appear to be random because they actually go through a 0:14:39.840 --> 0:14:44.040 very complicated system in order to get a specific product. 0:14:44.480 --> 0:14:47.720 But if you were to understand all the steps, you 0:14:47.720 --> 0:14:50.520 would see that it's not truly a random number because 0:14:50.520 --> 0:14:55.160 computers are not good at creating true random numbers. They 0:14:55.200 --> 0:14:59.560 can just simulate random most of the time anyway, So 0:15:00.520 --> 0:15:03.280 you tend to use a very complicated process, but it's 0:15:03.480 --> 0:15:06.640 entirely deterministic. So that does mean that if you knew 0:15:06.960 --> 0:15:09.720 every single step of the process, and you had enough 0:15:09.760 --> 0:15:13.520 time and enough smarts, you could get to the answer 0:15:14.120 --> 0:15:16.840 that the computer is using. In fact, if you're good 0:15:16.960 --> 0:15:18.840 enough and you're fast enough, you could do it to 0:15:18.840 --> 0:15:21.200 the point where you could predict what the next thing 0:15:21.480 --> 0:15:24.360 is going to be, and you could actually in advance 0:15:24.480 --> 0:15:28.400 tune to the correct frequency every single time if you 0:15:28.480 --> 0:15:30.920 had all the information that the system was using in 0:15:31.000 --> 0:15:34.080 order to generate this stuff. But again, if you were 0:15:34.120 --> 0:15:36.040 just to look at it, it would appear to be 0:15:36.080 --> 0:15:39.680 totally random because it's such a complicated system that's going 0:15:39.720 --> 0:15:42.480 through before it gets to that that solution, and the 0:15:42.520 --> 0:15:48.000 processes tend to be really super fast, like changing frequencies 0:15:48.080 --> 0:15:51.440 at least twice a second, and that's a slow one. 0:15:52.080 --> 0:15:55.480 Most of them change frequencies way more frequently than two 0:15:55.520 --> 0:15:58.200 times in a second, which means it's way too fast 0:15:58.200 --> 0:16:01.360 for a human to be able to replicate any a Typically, 0:16:01.560 --> 0:16:03.600 the way this might work is you would have two 0:16:03.840 --> 0:16:07.880 radio transmitters and receivers or radios, let's just say, and 0:16:07.920 --> 0:16:10.240 you want them both on the same series of frequencies. 0:16:10.480 --> 0:16:13.360 So you you make some sort of process that generates 0:16:13.360 --> 0:16:16.080 what appears to be a random number, and that this 0:16:16.160 --> 0:16:19.400 number is somehow associated with frequencies, typically in a look 0:16:19.440 --> 0:16:22.680 up table. So you could say, like, if the number 0:16:22.880 --> 0:16:27.280 is fourteen, you look at this table, this chart, and 0:16:27.320 --> 0:16:30.160 it tells you what sequence of frequencies you need to 0:16:30.280 --> 0:16:34.280 use for that communications session. So your first radio will 0:16:34.320 --> 0:16:37.720 send a request to radio number two. Radio number two 0:16:37.760 --> 0:16:43.080 responds with a seed number generated by this pseudo random process. 0:16:43.120 --> 0:16:45.560 So Radio one says, hey, I want to chat. Radio 0:16:45.600 --> 0:16:50.440 two says, use this number. Radio one ends up using 0:16:50.440 --> 0:16:53.240 that number and looks up the series of frequencies, sends 0:16:53.280 --> 0:16:57.080 that back to radio two for a confirmation. Uh, the 0:16:57.080 --> 0:16:59.480 these are the sequence of frequencies that the two radios 0:16:59.480 --> 0:17:02.400 are going to use for the duration of their communication session, 0:17:02.920 --> 0:17:07.160 and then the radio two will confirm that by sending 0:17:07.200 --> 0:17:11.520 a synchronization signal to radio one that makes both radio 0:17:11.680 --> 0:17:15.679 start on the same moment and then they can communicate. 0:17:15.720 --> 0:17:19.840 They will swap frequencies, not just knowing which frequency it 0:17:19.960 --> 0:17:24.560 goes next, but how long each frequency will be landed upon, right, 0:17:24.600 --> 0:17:27.960 how long do you spend on each individual frequency? And 0:17:28.000 --> 0:17:31.200 that allows for the communication between these two devices where 0:17:31.240 --> 0:17:34.760 you're you're hopping from one frequency to the next throughout 0:17:34.800 --> 0:17:39.760 the entire session. And once you do that, you would 0:17:39.800 --> 0:17:44.120 appear to be hopping too frequencies at random from the 0:17:44.200 --> 0:17:47.840 perspective and of an outside observer. So if you and 0:17:47.880 --> 0:17:50.919 your buddy are chatting with each other over cellular phones 0:17:50.960 --> 0:17:56.840 that are using frequency hopping spread spectrum approach, then I 0:17:56.960 --> 0:18:00.399 when I'm looking at the signals that are you're sending 0:18:00.440 --> 0:18:01.840 back and forth to me, it would look like it's 0:18:01.840 --> 0:18:05.040 totally random, like there's no meaning from one frequency to 0:18:05.080 --> 0:18:08.880 the next. You're not sequentially hopping frequencies, you're jumping all 0:18:08.920 --> 0:18:12.639 over within that that bandwidth, whatever that band of frequencies 0:18:12.720 --> 0:18:15.760 happens to be. You could be jumping left and right, 0:18:15.880 --> 0:18:18.960 you know, up and down all sorts of ways, and 0:18:19.000 --> 0:18:21.920 I would not be able to determine where you're going 0:18:21.960 --> 0:18:25.640 to go next. That's really important for a multiple reasons, 0:18:25.640 --> 0:18:28.560 not just the idea of not being snooped upon, that's 0:18:28.560 --> 0:18:32.679 a big one, but also avoiding interference. Uh, you can 0:18:32.720 --> 0:18:36.000 have multiple devices all communicating through the same methodology, and 0:18:36.040 --> 0:18:38.920 because they're all using different frequencies and hopping around a lot, 0:18:39.520 --> 0:18:44.080 then the odds of two communication devices needing to use 0:18:44.119 --> 0:18:46.880 the exact same frequency at the exact same time are 0:18:47.000 --> 0:18:51.120 very very low. Also, these devices tend to be very 0:18:51.240 --> 0:18:54.439 low power devices, and because of that, they have a 0:18:54.480 --> 0:18:57.359 limited range. So once you get outside of that range, 0:18:57.640 --> 0:19:00.560 you don't really have to worry about interference anymore. So 0:19:01.080 --> 0:19:04.720 two mobile phones that happened to hop on the same frequency, 0:19:05.720 --> 0:19:07.720 that's only gonna be an issue if they were really 0:19:07.720 --> 0:19:12.520 close together, otherwise the signals won't propagate far enough. And 0:19:12.560 --> 0:19:16.880 again these happen. It happened so fast, within a split second, 0:19:17.480 --> 0:19:20.280 the odds of it actually causing any real interference are 0:19:20.320 --> 0:19:24.840 extremely low, and any interference that's perceptible to human beings 0:19:25.359 --> 0:19:30.600 that's almost impossible. So it you want to make sure 0:19:30.680 --> 0:19:33.520 that you have this this methodology set up in your 0:19:33.560 --> 0:19:36.639 system in a way that appears to be pseudo random 0:19:36.720 --> 0:19:38.840 to make sure you keep it secure and to keep 0:19:38.840 --> 0:19:42.120 it from interfering with all the other systems that are 0:19:42.119 --> 0:19:45.359 out there. Uh. One nice thing about this is that 0:19:45.440 --> 0:19:47.840 again you can use those multiple devices in that same 0:19:47.840 --> 0:19:51.560 frequency channel, and typically there are enough subchannels to allow 0:19:51.640 --> 0:19:54.280 lots of multiple devices to access the system without any 0:19:54.280 --> 0:19:57.879 sort of cross talk or interference. So WiFi uses this. 0:19:57.920 --> 0:20:01.080 For example, when I did the WiFi episode, I talked 0:20:01.240 --> 0:20:05.359 briefly about the strategy called frequency hopping spread spectrum or 0:20:05.520 --> 0:20:08.760 f h s S. A spread spectrum is a method 0:20:08.800 --> 0:20:11.520 in which a signal is spread throughout the frequency domain 0:20:11.640 --> 0:20:15.480 of a bandwidth. So let's just say, for argument's sake, 0:20:15.560 --> 0:20:18.880 we've got a bandwidth of channels. There are ten essential 0:20:19.119 --> 0:20:22.960 essentially sub channels inside this bandwidth, so you can think 0:20:22.960 --> 0:20:24.960 of it as a highway that has ten lanes of 0:20:25.080 --> 0:20:29.399 potential traffic. A spread spectrum would take a signal that 0:20:29.480 --> 0:20:32.320 normally would fit into just a single channel or a 0:20:32.320 --> 0:20:35.720 single lane on this highway, and then allow that signal 0:20:35.760 --> 0:20:40.560 to spread through the entire width of that bandwidth or 0:20:40.720 --> 0:20:43.520 all of the lanes of the highway. With frequency hopping, 0:20:43.720 --> 0:20:46.160 it would be as if the car was magically jumping 0:20:46.200 --> 0:20:48.920 from say, lane to to lane seven, and then from 0:20:48.960 --> 0:20:51.359 lane seven to lane five, and then lane five to 0:20:51.440 --> 0:20:54.119 lane one, and so on and so forth, just immediately 0:20:54.520 --> 0:20:57.920 jumping from one lane to the next while continuously traveling 0:20:57.960 --> 0:21:01.880 down the highway. But there are other methodologies that take 0:21:01.920 --> 0:21:06.359 a slightly different approach. Direct sequence spread spectrum, which is 0:21:06.400 --> 0:21:09.879 also used in WiFi, takes the signal and then modulates 0:21:09.880 --> 0:21:12.800 it with a pseudo random noise spreading code, and the 0:21:12.840 --> 0:21:16.320 result is that tiny bits of data travel through different 0:21:16.320 --> 0:21:21.080 frequency subchannels. So with frequency hopping, you have this big 0:21:21.160 --> 0:21:25.119 highway with ten lanes, and the car is in any 0:21:25.240 --> 0:21:28.480 one lane at any given time, but just one lane, right, 0:21:28.640 --> 0:21:31.080 It's like either in lane two, or it's in lane 0:21:31.080 --> 0:21:34.879 three or whatever. And then when it comes time to hop, 0:21:35.440 --> 0:21:38.800 it suddenly appears in a different lane, but it's always 0:21:38.920 --> 0:21:43.359 only in one lane at a time. Direct sequence spread 0:21:43.400 --> 0:21:47.040 spectrum is different. It's in all the lanes simultaneously, but 0:21:47.080 --> 0:21:50.639 only tiny parts of it are in each lane, and 0:21:50.680 --> 0:21:52.399 then on the other end you're able to piece it 0:21:52.440 --> 0:21:58.240 all together. So different approach to using the same sort 0:21:58.280 --> 0:22:00.960 of trying to solve the same sort of problem. So 0:22:01.080 --> 0:22:04.679 it's the basis d S S S. The direct sequence 0:22:04.680 --> 0:22:07.600 spread spectrum is the basis of c d M A 0:22:07.760 --> 0:22:11.480 mobile phone technology, and then the frequency hopping spread spectrum 0:22:11.560 --> 0:22:15.240 is the underlying technology for G s M mobile phones. 0:22:16.160 --> 0:22:19.960 Most of the world used g s M for mobile 0:22:20.000 --> 0:22:24.000 phone technology, at least before the development of lte A 0:22:24.119 --> 0:22:26.120 T and t n T Mobile were the two companies 0:22:26.160 --> 0:22:28.640 in the United States that relied on g s M tech, 0:22:29.320 --> 0:22:31.359 and then c d M A was only used in 0:22:31.400 --> 0:22:34.000 a couple of places in the world, primarily the United 0:22:34.040 --> 0:22:39.520 States under Verizon and Sprint. In WiFi, the typical approach 0:22:39.560 --> 0:22:42.080 with f H S S was to use one of 0:22:42.160 --> 0:22:46.119 seventy nine different one mega hurts channels following one of 0:22:46.240 --> 0:22:50.080 seventy eight different hops sequences, and the sequence would require 0:22:50.119 --> 0:22:53.920 hops every four hundred milliseconds. The odds of interference, whether 0:22:53.960 --> 0:22:57.240 intentional or otherwise, we're really low. To reduce the chance 0:22:57.280 --> 0:23:01.120 of interference even more, like I said, these technologies were 0:23:01.200 --> 0:23:06.359 using very low power transmissions, uh typically around one what 0:23:06.760 --> 0:23:09.480 or less in power. And you may remember in that 0:23:09.520 --> 0:23:12.800 recent episode about WiFi how the spectrum set aside for 0:23:12.840 --> 0:23:16.400 WiFi communication happened to be within the range of industrial 0:23:16.520 --> 0:23:20.160 and medical equipment and also stuff like microwave ovens. So 0:23:20.640 --> 0:23:24.439 in the United States, the FCC had said, this band 0:23:24.560 --> 0:23:28.840 of frequencies is set aside for these particular types of technologies. However, 0:23:29.600 --> 0:23:34.240 if your technology can transmit at a power level below 0:23:34.560 --> 0:23:38.760 one what or so, then you may also make use 0:23:38.800 --> 0:23:44.040 of this and unlicensed approaches to this this band of frequencies. 0:23:44.080 --> 0:23:47.680 That's where WiFi rose up out of the unlicensed use 0:23:48.040 --> 0:23:51.360 as long as they remained in the transmission power below 0:23:51.920 --> 0:23:56.359 the threshold. So that also meant that the potential of 0:23:56.400 --> 0:24:00.000 interference was decreased because again those signals could not try 0:24:00.080 --> 0:24:02.280 will very far, they just didn't have a lot of 0:24:02.640 --> 0:24:06.800 behind them. H f HSS has been used in multiple 0:24:06.840 --> 0:24:10.879