026 Wireless Text Messages without Cables or Modems: Rattlegram (OFDM)

What a fantastic idea! The Rattlegram app for Smartphones transmits data using our radios' microphones and loudspeakers. With more than double the speed of APRS. How is this possible without cables to the handheld? And what is the relation of this project with Wi-Fi, 4G, and 5G? Stay with me. I will tell you an interesting story.
Links:
OFDM Modem: github.com/aicodix/modem
Zero Retries Newsletter: zeroretries.substack.com/
Baofeng UV-5R (not allowed in EU and CH): amzn.to/3W0P2KU
Ailunce HD1 DMR radio (used in this video): amzn.to/3Pf4Szo
Anytone AT-D878 (better choice, but currently not allowed in CH): amzn.to/3UR4eJI or s.click.aliexpress.com/e/_Dci...
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[@rkirke1]

Brilliant idea and implemented perfectly for the smart-phone era! I remember in the early 2000s I worked at a small internet company and stunned one of my colleagues (who was well versed in IT, but not radio). I installed an early piece of PSK31 software on both of our PCs (which were several meters away in a fairly noisy office environment, and had 90s style PC speakers and electret "stalk" microphones). I told him to go ahead and unplug the ethernet cable from his computer which he did. After a few warbling sounds from my PC, messages from me started appearing on his screen as I typed. He was dumbfounded at first and then quite impressed once he worked out what was happening :D I'm impressed that the KZbin MPEG audio compression didn't affect the reception of the Rattlegram whatsoever! Merry Christmas & a happy New Year to Andreas, Ahmet and all the viewers!

[@HB9BLA]

Nice story! Indeed, I was also impressed that it worked on KZbin. We did tests with DMR and there it did not work at all.

[@DrBovdin]

@@HB9BLA the reason why it didn’t work on DMR I suspect might be because the compression protocols there are optimised for voice readability and are much more aggressive than e.g. mpeg is even at lower bit rates. The goal of mpeg as used in YT et c. is to reconstruct as much as possible of the in-spectrum at the output without voice optimisation (I wouldn’t be surprised if other voice codecs would similarly destroy the message).

[@farrenconstable]

Not first, but message is "Dear viewers, I wish you Merry Christmas and a happy New Year". Took about a dozen tries to get volume levels and positioning correct. Very interested in a future series on GNU Radio! Merry Christmas to you as well!

[@HB9BLA]

Correct!

[@stevenm45]

A nice intro into the world of OFDM which is also used for our dvb-t & dvb-t2 standard & high-definition terrestrial TV broadcasts.

[@HB9BLA]

Indeed, Ahmet did also SSTV applications. So far I never looked into it.

[@joshe1165]

@@HB9BLA I believe the Vesa HF digital mode for Winlink is also OFDM, but I could be wrong there.

[@radiotests]

@@HB9BLA Ahmet has Angel backers in the Ham community. They will be at the Ham cation in Florida. It's all very interesting and used in the VHF and above the potential seems amazing!

[@MichaelBransonCoach]

Very interesting and thank you. I was looking at using codec2 over lora a while ago but got distracted. This beautifully clear explanation of ofdm has inspired me. I think I'll revisit it.

[@HB9BLA]

I am interested in your results, too!

[@SchwaAlien]

I have fond memories of programming games found in magazines into my first computer (the TI99) and saving and loading the programs using audio cassettes, so this seems like a modern evolution of that early 80’s tech... no doubt it was incredibly low bps, but it was surprisingly reliable despite the cheapness of the generic portable audio cassette recorder. I like how the error correction is built in, the same kind of thing was present on usenet for large files broken into multiple parts that would often have most but not always all the pieces, you were able to re-create a missing file or two from the other files as long as there was enough and this worked quite reliably to collect a bunch of cracked Dreamcast GD-ROM games from that old forgotten but not totally abandoned part of the early internet.

[@HB9BLA]

I also started with a TRS-80 and a cassette deck. But frankly, after the invention of the Floppy Disk, never looked back ;-) A lot of technology comes back in "new clothes" after years, I think. Like the electric cars ;-)

[@f1sls]

Thanks for the wishes! And my Rattlegram was listening while you sent your demo at 0:08 and I received "HB9BLA - The quick brown fox jumps over the lazy dog" and "HB9BLA - Decoding failed"... 😂😂😂 73!

[@HB9BLA]

Very good!

[@TheAndjelika]

.... "Dear viewers, I wish you Merry Christmas and happy New Year." This app is great, and since I am someone who was in 8 bit computing from 1980, girl now woman who loved to code on 6510, and Z80, and still love it, from machine language, assembler to high end languages, also woman who was playing a lot with HAM radio, took serious part in radio clubs ar that time, I know how beautiful was time when we were recording our data on the tapes. I can say that Era when AD and DA start becoming daily routine was magical time. Now we are mostly only D, D, D... but analogue can't disappear just like that

[@HB9BLA]

Very rare to read a comment from a woman on this channel with 99.5 male viewers! So we experienced similar things in the 1980. For me, still everything is analog in the end, but simplifying it with a digital model and throwing millions of cheap and small transistors on it gives great possibilities (as we see here). I feel I currently live in an electronics "land of milk and honey".

[@TheAndjelika]

@@HB9BLA Dear, I don't think it is rare, only women are mostly pushed to the side, usually when they are young. There are many women scientist, electronics experts, and hackers. When you open up your male boxes and egos, you will see it is actually a lot.

[@HB9BLA]

​@@TheAndjelika First: I would be extremely glad to see more women in our domain. All I saw were excellent. And I first thought that this was a Swiss problem. But my main (electronics) channel with 400'000 subscribers always had around 99% male viewers (according to KZbin statistics). So I thought it was a global fact. In which country do you live? BTW: My KZbin relationship manager told me that my channel has a higher male percentage than gaming channels (which are also bad in this respect).

[@TheAndjelika]

@@HB9BLA Dear, they support girls, your daughters, granddaughters, don't buy them some dolls, get them tools, show them how to solder. I need to be honest with you, like year ago I was about to fully leave your channel because of a few sentences you've said... they were on edge of sexism, showing that only men are welcome here, and women should be somewhere else. One of the first steps is to develop sensibility and really invite all people to watch your channel, and to promote that in every moment you can. Happy holidays! Andjela

[@nickandjessica]

​@@TheAndjelika jajajjaa 50/50 my ass, so funny to see you try to debunk the 99.5% statistics of male viewers found in KZbin studio for channel owners jajajajjaa feminism is gay

[@scottwood1143]

Great fun, _and_ educational! Before I finished watching I had loaded the app (Android Pixel6) and decoded your message (first try).

[@HB9BLA]

Cool. I wonder how many downloads he had today...

[@cptcrogge]

Decoding worked fine with normal PC speakers. I wish you a happy new year as well!

[@HB9BLA]

Thank you!

[@VladoNejaky]

Message is "Dear viewers, I wish you Merry Christmas🎄⛄ and a happy New Year" 🙂

[@HB9BLA]

Yes!

[@rbmwiv]

I was fixing to say that but you beat me to it. Rattle gram is awesome. I want to build a server on a R pi on my repeater. I like having a bulletin board like that. Awesome stuff friend.

[@Katanium]

Thanks for wishing us a merry Christmas and a happy new year. I wish you the same too! :)

[@HB9BLA]

:-)

[@chrisjohnson8741]

And a Merry Christmas and a Happy New Year to you, too!

[@HB9BLA]

Thank you!

[@olpqay]

1:24 "Decoding failed" 😅🔊 Have a great sunday, Andreas ;) Thanks for your content!

[@HB9BLA]

It seems you need to enter your Callsign first.

[@nicolasborj8831]

Pointu, efficace, super travail merci

[@HB9BLA]

De rien!

[@pasjeihobby]

This is amazing ! My head is hot after taking so much info but technology is worth of it.

[@HB9BLA]

Indeed, it is not easy ;-)

[@ratbagley]

Andreas, I think this is a great idea but I don't have any suggestions. I will definitely follow this so I can use it at my cabin in the mountains. Thank you for your service to our hobby for so many years. Jeff

[@HB9BLA]

You are welcome!

[@zaphhood4745]

Merry Christmas and a happy new year to you also.

[@HB9BLA]

Thank you!

[@alexosol2975]

Mt63 is OFDM mode which is widely used in e.g. prepping community for years. And yes, cable is not required for this mode too.

[@HB9BLA]

Thank you for the link. I did not know this protocol.

[@ly2ss]

@@HB9BLA Q15X25 by the same author is also quite interesting.

[@catcam]

Many thanks for that Andreas.

[@HB9BLA]

You are welcome!

[@Friendroid]

Coincidentally, a few days ago I found a website showing how to send images captured by an ESP-32CAM through SSTV using these radios. SSTV transmission seems very interesting. Thank you for your videos and best wishes for 2023!

[@HB9BLA]

Ahmet dis some SSTV before this project, too.. Happy 2023 to you, too.

[@Burn0u7]

Can you share a link?

[@R4YTUBE]

Thank you so much. This video was really interesting.

[@HB9BLA]

You are welcome!

[@santoshbansode697]

Good morning sir your both youtube channel are very good and informative,,,, and it helps us lots,,,,,,,i again thanks to you for making these channels,,,,,,,, very few people do this,,,,,,,,, with ❤️,,,,,,,

[@HB9BLA]

Glad you like my content!

[@Torticolim]

Merci Andreas pour cette découverte, Joyeuses fêtes de fin d'année... Frohe Festtage, 73's, HB9DVD, Marc

[@HB9BLA]

Vielen Dank! Dir und deiner Familie ebenfalls Frohe Weihnachten und einen guten Rutsch ins neue Jahr.

[@dazoedave]

Merry Christmas to you as well.

[@HB9BLA]

Thank you!

[@siberx4]

At first I thought you were trolling us, because my first few attempts correctly decoded your callsign but gave "Decoding failed" as the message (as if that's what had been transmitted - the app could use some user interface improvements). Sticking the phone closer to my headphone cup finally got a successful decode, though! Very cool app, and I hope to see future improvements in this kind of easily accessible use of high-tech encoding. It's sad to me that there's seemingly a big divide in the amateur radio community where a majority of the hobby is "caught in the past" and unwilling or uninterested in combining the extremely capable modern encoding schemes and digital processing tools we have available with the very powerful and useful transmitters and frequency bands that hams have access to. There's all kinds of cool things you could do with encoding modes like this on HF for example, but every time I search for projects doing this kind of thing, I always end up at abortive or abandoned attempts that never really took off (with a few limited exceptions). Too many hams are satisfied with either their simple old SSB and FM audio modes, or happy to rely on weird proprietary clunky windows applications made 15 years ago that are awkward to interact with or don't run on many types of systems. This is not to say those modes don't have a place, but amateur radio was originally created to allow experimentation and development of this newfangled "radio" technology, and in many ways the community is reluctant to advance much past the 1950s. Modern open-source design methods seem like a perfect match for the sharing-friendly and experimental ethos of amateur radio, but somehow the two are rarely enthusiastically used together.

[@xdsopl]

The preamble symbol in COFDMTV, that contains the call sign, is designed to be much more robust than the payload symbols, so we have a high probability to find out who is transmitting. Indeed, the UI needs improvement with the handling of errors. Thank you for the feedback.

[@HB9BLA]

In the board of the Swiss HAM Radio organization, I am responsible for modern technologies (all invented after 1980). After a short time, I decided not to care about the ones not interested. They love their hobby and are happy with it. I focus on the ones interested in this tech. This is part of the motivation to create this channel.

[@sdjhgfkshfswdfhskljh3360]

Lots of FT8 transmissions in the air means that there are enough interested people. Also WSJT-X is open source. This is enough for me to not be worried too much.

[@fritzx720]

Hello Andreas, thank you for the excellent explanation. Installed the App, set my Callsign and it worked right out of the box: 2 x the jumping brown fox and the Christmas wishes which are returned from the Black Forrest to CH. Viele Grüße

[@HB9BLA]

Correct! All three messages.

[@cemaxecuter7783]

Excellent video, thanks for sharing!

[@HB9BLA]

You are welcome! Thank you for your distribution! Maybe you send me an email or a Facebook messenger message? I would like to use your project for my future SDR projects.

[@cemaxecuter7783]

@@HB9BLA sure thing! That’d be great.

[@jamesmichener7526]

Once again an excellent video. You should look at VARA and VARA FM

[@HB9BLA]

Unfortunately, these modems are not open source :-(

[@urrick33333]

That is extremely intertesting topic. I tried to do something similar actually.. Didn't finish it, but it seems like an awesome opportunity to start again :)

[@HB9BLA]

Indeed, a good chance!

[@sdjhgfkshfswdfhskljh3360]

Nice thing about such project that it can be perfected indefinitely.

[@AdityaMehendale]

A semester's worth of comms-101-theory explained in 13 easy-to-digest minutes. Bravo :)

[@HB9BLA]

Thank you for your kind words. I started with a course in modern communication. As said in the video, this topic is not easy for me. I did this kind of math 40 years ago.

[@maximus6884]

Wow building our own modulators and demodulators for these sound interesting.

[@HB9BLA]

I agree!

[@mahudson3547]

You can’t beat Nyquist - or can you? Fascinating technology. Very Happy Christmas to you

[@xdsopl]

You can't but you can get arbitrarily close to its limit 😉

[@HB9BLA]

Merry Christmas, too!

[@sdjhgfkshfswdfhskljh3360]

Frequency is only one of parameters which defines message capacity. Another two are power and time. If you have very loud signal, you can put more data into it. However at some point sound turns into shockwave, so there is a limit here too, sadly. But looks like time is unlimited.

[@mahudson3547]

The comment was about data rate which is per unit time

[@sdjhgfkshfswdfhskljh3360]

@@mahudson3547 anyway SNR can vary.

[@AmeyKshirsagar]

Hi. I have built something similar to Rattlegram and achieved 250 characters/sec speed on Aspera V-9. I have made some patch wires using off-the-shelf wires for headsets of WTs & phones to avoid the mixing of ambient noise or disturbance. Due this I was able to achieve a proper audio. However the audio frequency ranges of different WTs requires certain changes in the app's code and trial and error on volume of reception on listening side

[@HB9BLA]

Ahmet Limited the number of channels because he also experienced bandwidth differences. Your speed is quite impressive.

[@praveenb9048]

Some first generation computer modems had a cradle in which you placed your landline phone's handset -- so it was acoustic coupling between phone and modem.

[@HB9BLA]

I remember them, too. But they used simple modulations.

[@ArindamGhoshal]

Dear viewers, I wish you Merry Christmas🎄⛄ and a happy New Year

[@HB9BLA]

Correct!

[@ArindamGhoshal]

@@HB9BLA wish you merry Christmas and happy new year also. Stay well. DE VU3EZX.

[@HB9BLA]

@@ArindamGhoshal Thank you!

[@chuxxsss]

Merry Christmas Andreas.

[@HB9BLA]

Thank you! Same to you.

[@joinedupjon]

I found it worked very well through my laptop speakers - though I could get 'decoding failed' by moving the phone further away than about 2m... but it always seemed to know the sender was HB9BLA - so I wonder if there is additional error correction for the sender id? though I'm not the first "Dear viewers, I wish you Merry Christmas :christmas_tree: :snowman: and a happy New Year" Congratulations to Ahmet on a successful implementation and coming up with a very catch name for it.

[@xdsopl]

The preamble symbol in COFDMTV, that contains the call sign, is designed to be much more robust than the payload symbols, so we have a high probability to find out who is transmitting. Compliments are always welcome and motivating.

[@stewartrv]

Very interesting. I'd love to make a couple of dedicated devices using a pair of cheap BF888's and attached directly to a USB sound card just as done with use of Allstar nodes. We could take care of pressing ptt and reduce audible noise in that case. 73.

[@HB9BLA]

Should be possible. It seems you can add noise befor the transmission to trigger the VOX

[@Richardincancale]

DRM (Digital Radio Mondiale) uses OFDM with QAM modulation of the sub carriers. There is an amateur radio version of DRM using open source software on a PC

[@HB9BLA]

I had a quick look at DRM. An interesting project combining old AM technology with newer Smartphones!

[@TheGmr140]

a great video, thanks

[@HB9BLA]

Glad you enjoyed it

[@ProGamer-xl9po]

Very interesting.

[@HB9BLA]

Glad you think so!

[@bobingridshaw5361]

Dear viewers, I wish you Merry Christmas and a happy New Year

[@HB9BLA]

Yes!

[@martinalcock7632]

The equations for the DFT are for the continuous time domain, not the discrete time domain as would be used in an OFDM modulator/demodulator. Some carriers are also designated as pilots with fixed magnitude and phase for equalization and timing recovery, therefore not all carriers can be utilized for data.

[@HB9BLA]

You are right.

[@DunOpondo]

This is interesting!

[@HB9BLA]

Thank you!

[@jmr]

This is very interesting.

[@HB9BLA]

Thank you!

[@christophtack5080]

David Rowe developed the Fdmdv modem for use with his CODEC2 voice codec. That modem seems very similar to the one presented here. Unfortunately that modem is deeply embedded in the freedv application. I haven't seen it being used for non-voice data.

[@HB9BLA]

Thank you! Interesting links. I will have a look at these projects.

[@jamesdinsmore9022]

Thanks!

[@HB9BLA]

Thank you for your support!

[@bigmoney8194]

a beautiful initiative so much more beautiful if I can do it,

[@Thomas72B]

Received: Dear viewers, I wish you Merry Christmas and a happy New Year

[@HB9BLA]

Yes!

[@Crazy--Clown]

Very good video Thankyou Fritz

[@HB9BLA]

Thank you!

[@VK2GPU]

"Dear viewers, I wish you a Merry Christmas🎄☃ and a happy New Year" Worked first time decoding :)

[@HB9BLA]

Correct!

[@noimnotarobotcanubeleiveit7024]

merry xmas to you too!

[@HB9BLA]

Thank you. Same to you!

[@TechwithStefan]

super nice video :)

[@HB9BLA]

Thanks for the visit!

[@LMB222]

I've tried implementing this… lack of access to the full I and Q means you either have to use FSK (slow), or synchronise the phase before every transmission if you want OFDM . I'm going to check this out!

[@HB9BLA]

You are right. Synchronization is very important.

[@LordDevi]

"Dear viewers, I wish you Merry Christmas and a happy new year." That was the message I got. Merry Christmas to everyone.

[@HB9BLA]

You got it right!

[@lezion]

Hey, I would love to build multi-digital radio based on CM4 pi supporting m17 digital mode too. It would be good if you covered that mode too.

[@HB9BLA]

Thank you!

[@sharpbends]

Very interesting :-)

[@HB9BLA]

Glad you think so!

[@EsotericArctos]

Sometimes I miss the old days of just AM. It is nice to talk on. With digital transmissions though, AM just doesn't cut it. For digital, I do like OFDM, but for analogue voice, I like the old fashioned AM.

[@HB9BLA]

There is no "either or", I think. There are still enough people interested in old tech.

[@stephanesmith3360]

Dear viewers, I wish you a Merry Christmas and a happy New Year!

[@HB9BLA]

Correct!

[@firstreactor8983]

Excellent video. Thanks! I'm assuming this would work between two Baofengs with K2 cables to thier respective phones. I'd expect this to improve reliability, yes?

[@HB9BLA]

I think so, but did not try

[@firstreactor8983]

@@HB9BLA Tried this and it worked. Here is the setup: HT setup (both HTs) HT model: Frequency: Wide (25 KHz) Power : Low (HTs at opposite end of 12' room) Vox: On, level 3/4 out of 7. (One level on each HT. 7 is most sensitive). Squelch: 1 (Zero is open squelch). Volume: 1/4 turn from off. Dual watch: off Receive power save: off. Cable setup Baofeng standard cable (K1) and Baofeng APRS cable (K2). Phone setup Phones: recent Motorola Androids. Volume: 3/4 or slightly less. Decoding does not work if transmitting phone's volume is too high.

[@mcconkeyb]

Yup, I'm in. Well in as far as I can be with the very limited free time I've got. :-)

[@HB9BLA]

It will be spread over time...

[@sdjhgfkshfswdfhskljh3360]

I made similar software many years ago. At this moment it uses BPSK. One problem with OFDM that is not mentioned in this video is that with bad microphones and speakers it is possible to completely lose part of frequency range, which means that some subcarriers will be completely destroyed. That's why I decided not to use it. Without OFDM my program have problems with multipath propagation, yes, but 2-3kbit/s are still achievable even with lot more primitive modulation.

[@HB9BLA]

I agree. For me I agree that the frequency response of the channel is important. For me, this tool was just an introduction into OFDM. I do not think that microphones and loudspeakers are a good thing without humans...

[@nonchip]

i like the bit where you said "they" call a FT an "Inverse function of the IFT" :D not sure which "they" do that but i always just called the inverse of the inverse of a thing that thing :P joke aside great video though, learned a lot :)

[@HB9BLA]

They are the guys to understand it ;-)

[@matthews2585]

I have a couple of questions if I may. I presume this will work if you use a k plug repeater connecting from the mobile phones 3.55mm jack? Also will this work where dcs is set on a channel? Thank you.

[@HB9BLA]

The audio just has to be able to travel from the Smartphone to the transceiver.

[@kennethng8346]

Does anyone know if this method is similar or not to what the Trailblazer modems used back in the late 80s? I remember reading a description where it divided the bandwidth up into a hundred or so channels and did all the encoding/decoding in software.

[@HB9BLA]

AFAIK OFDM was not used back then. The chips were not capable...

[@jankkhvej]

@@HB9BLA Trailblaizer's PEP was based on OFDM, those modems was a revelation for uucp. Never forget their line signals, it's a music for my ears.

[@HB9BLA]

@@jankkhvej I now read the story of Trailblazer PEP. Indeed, this was revolutionary back then. And they needed quite expensive chips for "just" a modem...

[@PortableRadio]

Thanks Andreas for this interesting OFDM demonstration. Unfortunately, I could not decode your message, got always "From HB9BLA1 Decoding failed". Previously, I entered my call and experimented with different audio sources. Anyway, great idea and well explained! 73 Stephan

[@HB9BLA]

You are welcome! Others were successful. So I do not know why it did not work with your setup.

[@thuff3207]

Very interesting, I wonfered when higher bit rates would come to ham radio.

[@HB9BLA]

They are already here in other areas like HAMnet or AREDN ;-) But on the lower bands there are opportunities.

[@davey2k12]

That's badass 😱

[@HB9BLA]

:-)

[@aquahood]

Encryption is not allowed on amature bands but could you use ultrasound as as long as you use of the accepted and published modulation types just shift the frequency to inauable?

[@HB9BLA]

As long as you do not encrypt, you are safe.

[@decibel_tastic2869]

Forward (typo). At RF, COFDM is not a cure-all it does have the Peak-to-Average power issue requiring highly linear, inefficient, and complex RF amplifiers. Whereas, GSM uses GMSK and tolerates non-linear efficient simple Class-C amplifiers.

[@HB9BLA]

You are right. This is why it is not used in low power applications.

[@WhiteLion1337]

Nice! Could you please make a tutorial about using Rattlegram ?

[@HB9BLA]

I showed all what is needed ;-)

[@NiHaoMike64]

Could encoding and/or decoding of Rattlegram be implemented on a microcontroller of some sort?

[@HB9BLA]

It needs quite a lot of power. Maybe Ahmet will try an ESP32-A1S

[@antoninperbosc1532]

@@HB9BLA prelookuptable or precalcul array could "help a lot to solve" compute problems with ram available on new µc remember what demomakers was beable to do with limited ressources 20 yeas ago !

[@MoisesCaster]

It would be possible to transfer small files by sound. Incredible.

[@EsotericArctos]

Even larger sound files could move across, depending on the compression of the files. :)

[@dv5809]

Not a new concept, this is how vintage computers like Commodore 64 stored programs, in 80' there were even some transmissions of programs in public radio

[@HB9BLA]

As DV writes, we stored our programs on cassette decks. But did not use these modern high speed protocols.

[@wandererkh]

It's time to recall 20 years old dial-up modems with speeds up to 56kbps

[@paaao]

I've been doing this using a hellscrieber app on my iPhone to text my kid over gmrs. No cables, just phones using internal mic and speaker held near the transceiver. Works great, even on the edge of range thanks to hellscrieber doing no decoding/forward error correction or checks. Try it out... I bet you $100 that you'll be able to read msgs at further range using hellscrieber as opposed to rattlegram.

[@HB9BLA]

Good to know. I do not know the Hellscriber protocol.

[@paaao]

@@HB9BLA I find that hard to believe having watched many of your videos. Look up feld hell, and hellschreiber. I'm probably misspelling it, but you'll find it. It was invented around the cw days.

[@HB9BLA]

@@paaao I know the name, but never used it to be precise. I was not active during the "packet times"

[@MarcinWloszczyk]

Message: Dear viewers, I wish you Merry Christmas and happy New Year. Great idea!

[@HB9BLA]

Correct!

[@matambale]

We've had digital modes since the invention of radio. In fact, it was the first mode.

[@HB9BLA]

I agree. I do not know your capability, but my morse speed never got higher than a bit over 2 characters per second...

[@matambale]

@@HB9BLA About 12 WPM or 1 character per second peak for me. A good bit lower now.

[@HB9BLA]

When I was young I worked as a professional radio operator…

[@matambale]

@@HB9BLA Very nice. I did teletype work as a young man; speed there about 10x Morse. Morse strictly by amateur radio. TTY machine was limited to 100 WPM if I remember this right.

[@alexflores7652]

It sounds like it is using a concept called data over sound. This idea is being considered for IoT as an added layer of security. Two of the software schemes to implement this are called Chirp and Listen.

[@HB9BLA]

What is the name of the project?

[@topannurhakim]

pinter banget bapake

[@HB9BLA]

Thank you!

[@cdevidal]

If you use cell phones to transmit and pre-shared encryption keys for the data, it becomes extremely difficult to censor, something we need in this age. I had thought of using a central server so that a group of friends could send and receive secret messages over cell phones. No not Signal, that uses the internet. Talking about voice calls just like in the video, over cell calls, not ham radio.

[@pete3897]

So there's this app called Signal...

[@cdevidal]

@@pete3897 Signal relies on the internet. I'm talking about making voice calls, just like in the video. I'll update my comment.

[@HB9BLA]

In HAM radio, encryption is not allowed.

[@cdevidal]

@@HB9BLA correct. Hence the need for cell phone calls.

[@RealJohnnyDingo]

as an added bonus you're adding random noise to the NSA database where they record all of our phone calls. won't compress very well either 😂

[@jeffjefferson2676]

Pretty interesting. If you were to send the sounds through a cable, could you use Rattlegram on HF? The mode does look very interesting. Greetings, Jeff

[@HB9BLA]

It should also work through HF. But it is not optimized for fading, etc.

[@p1366]

I wonder if this would work for under-water sonic communications..?

[@HB9BLA]

I do not know. Sonic coms is a very special topic.

[@richgarrett4082]

the quick brown fox jumps over the lazy dog

[@HB9BLA]

This is the second message. The one I asked was different.

[@nimoabo6458]

مضاعفة تقسيم التردد المتعامد (Orthogonal frequency-division multiplexing) وضع تعديل الإشارة في الاتصالات ، يعد تعدد الإرسال بتقسيم التردد المتعامد نوعًا من الإرسال الرقمي وطريقة لتشفير البيانات الرقمية على ترددات حاملات متعددة

[@HB9BLA]

على وجه التحديد

[@TomTalley]

Downloaded from play store. Input my call. Entered message and transmitted. Very interesting. Collins radio used sync cohesrant ofdm in their kineplex system back in the 50's. Their adoption of coherent psk, qpsk dropped the necessary noise floor 10's of dB. Isn't it a great world we live in. Thanks so much for the presentations you do. I'm just now picking up the esp32 python hobby partially because of your wonderful videos..73. de Tom W5XTT

[@HB9BLA]

Interesting that OFDM was already used in the analog tube times!

[@peterhume3474]

The implications of what this app can do has many important features. So.... if the internet, mobile phone network are down for any reason, but our smartphones can start up. I could communicate a serious text through UHF or VHF transceiver, say at a specific prearranged time and frequency, with another person ... and they can type an answer on their phone and send it back.

[@HB9BLA]

I agree.

[@PeterJavea]

@@HB9BLA Rattlegram would have really been able to help in the recent wild fires in Maui Hawaï. I live in Belgium and am a newbie ham (ON3VCF). Ispent that night up listening to the only SDR on the island going up and down the 10, 11, 2m and 70cm bands, listening to sporadic desperate transmissions of people trying to find people.... Normal FM was also down. But on 1110Khz am KAOI was on emergency programming trying to help. They were the only station I could find... (using also an app called "Planet Radio" For Several days I would tune into KAOI to listen in to the real people sharing real stories. One day a firefighter was talking about how all repeaters were out and that they'd had big difficulties getting through to base, etc. He mentioned about a new super-simple app called "Rattlegram" could have helped everyone. I have seen a few KZbin reviews of the app, and I don't think they understand its special characteristics and features. Specifically "Parrot".

[@DanielHofer]

Wish you Merry Christmas and a happy New Year too! 73 de Daniel, OE2DHH

[@HB9BLA]

Thank you!

[@DavidBarbarine]

I'm in!

[@HB9BLA]

:-)

[@wbehmann]

TNX for this cool idea. Tried it out but just getting a "Decoding failed", the CALLSIGN is transmitted. Neither the sound from the YT Video decodes (same message: Decoding failed" and also tried between two Anytone Handhelds over 2m. Call Sign is set on both sides. The two phones decode perfectly if there are next to each other. Any ideas? (Rattlegram 1.4)

[@HB9BLA]

It does not work over DMR for sure. Over analog and from KZbin it should work (at least it worked for many commenters)

[@wbehmann]

@@HB9BLA it was on analog. Direct connection.

[@AndreasSpiess]

@@wbehmann Strange. Obviously, no setup issue because it worked together. Did you pay attention that the respective microphones and loudspeakers were together? Did you hear the sound on the second handheld loud and clear?

[@cetyl2626]

But this is just the audio signal, right? The RF signal is still FM (The RF carrier being frequency modulated by the OFDM audio? Or am i missing something about the radios in the demo? Is the radio doing something different than FM?

[@HB9BLA]

In my case, the radios do. FM. But it does not matter. As you say, it is just an audio sound. Very versatile.

[@jensgoerke3819]

Decode worked after about 20 tries.

[@HB9BLA]

Very good!

[@rodo19724]

Hi !!! Greetings from Buenos Aires, Argentina. I bought two Baofeng Handies, the cheapest ones, the simplest ones, BF999S, how can I send data from DB9 to handy number 1, receive data on handy number 2, and decode it with arduino uno and RS232 module HW-044 ? , and show that data on a cheap OLED display like 1.3" (GND, VCC, SCL, SDA) Thanks so much !!!!!!!

[@kelvin0mql]

Love that the demo shows the 2nd smartphone's latest message to pop up says "Decoding failed" at 1:26. Also love that he's Rick-rolled himself.

[@HB9BLA]

It does not work all the time...

[@linuxranch]

Andreas, I'm not sure where sufficiently complex modulations cross the line to become "encryption" which isn't legal in some countries. In the US we have prohibitions on encryption, and requirements for station Identification. It appears that published compression methods are OK in the US, so long as the intent is to compress.. but, at some point, with "sufficient" error detection, the amount of "compression" compared to "overhead" becomes a loosing battle. How should we handle clear text station ID? Thoughts?

[@HB9BLA]

There are many discussions about encryption because the law was created before modern protocols. What they wanted to forbit is to have secrets. So I assume we should be able to use modern protocols and share the keys somehow. Then it would no more be a secret and therefore legal. Anyway, we have to solve this problem in the next years.

[@vk3fbab]

My understanding of prohibition of cryptography on ham radio is to ensure that anyone can listen. So by all means encrypt the signal just make the key public and include callsigns and stay in band. Here in Australia encryption is allowed for the express use of control of a remote or space device as well.

[@michaelchesbro8425]

This is a great app. I have been playing with it and it works well.... lots of fun. But I would like to know if there is a way to delete messages from the list once they have been seen? I don't see a way to do that. Thank you.

[@HB9BLA]

There is no way to delete messages. Ahmet wanted to keep it simple.

[@stevestroh1891]

I'll return the favor to HB9BLA with a review of this video in this week's issue of Zero Retries newsletter. HB9BLA does a GREAT job with this video.

[@HB9BLA]

Thank you, Steve! You do a great job, too.

[@jco997]

I tried rattlegram with a cheap microcasette recorder. It didnt work, as expected. I get "Preamble failure" error message. But these kind of errors was expected. Even a trivial DTMF decoder cannot work with my microcasette recorder. I was hoping that the 50% forward error correction could decode at least a single character from the microcasette, but no, it couldnt. 10/10 👍

[@HB9BLA]

Strange. A cassette recorder should be able to replay the frequency range. Maybe it is a problem of different speeds?

[@sdjhgfkshfswdfhskljh3360]

It is possible to analyze how exactly signal is corrupted by your hardware. And then select encoding (modulation) which is resistant to such corruption.

[@jco997]

@@HB9BLA I'm going to try this again. I was using a "GE 35375" microcasette recorder. I think it has something to do with this; en.wikipedia.org/wiki/Wow_(recording)

[@jco997]

It sounds like this when I'm playing back the audio kzbin.info/www/bejne/oXTag5eoe9l9q6c

[@Dednny]

You can use the simple Btech interface leads from android to the radio. Using Skype as an additional source allows you to dial up another android or laptop anywhere to send a Rattlegram msg. The device at the far end can have audio connectivity to a radio on vox and retransmit the msg in another part of the country thereby using Rattlegram as a pager. This takes a bit of tweaking. Does anyone else have an idea on how to use Rattlegram as a pager?

[@HB9BLA]

It seems that you can add noise before the transmission to open a VOX.

[@W4TRI]

Can I use a VOX APRS cable with this since I have it?

[@HB9BLA]

I think so. You only have to connect the audio.

[@jonarmani8654]

At what distance can you maintain 2800bps throughput?

[@HB9BLA]

I do not think that distance matters.

[@timbookedtwo2375]

There doesn't seem to be an iPhone version of Rattlegram, at least not in the German app store.

[@HB9BLA]

Not yet