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

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 RU-vid 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!

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.

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

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!

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.

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

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.

.... "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

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!

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.

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

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!

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

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

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

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

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.

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

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

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

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.

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 ❤️,,,,,,,

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

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.

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

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.

Pointu, efficace, super travail merci

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

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!

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

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 :)

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

Thank you so much. This video was really interesting.

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.

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

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

Merry Christmas and a happy new year to you also.

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.

Many thanks for that Andreas.

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.

Excellent video, thanks for sharing!

Merry Christmas to you as well.

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

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

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.

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

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.

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

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?

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

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.

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.

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

Merry Christmas Andreas.

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

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

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.

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

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

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.

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

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

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

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 :)

a great video, thanks

This is very interesting.

Thanks!

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

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 👍

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

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.

Very interesting.

This is interesting!

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

I do believe in the case of FT8 you're confusing OFDM (orthogonal frequency-division multiplexing) with OFMDA (orthogonal frequency-division multiple access). Your full journey of modulation is a little sparse too, it should go a little something like: AM, SSB, FM, PM, FSK, MFSK, PSK, Angle Modulation, CDMA (FHSS/DSSS), QAM, and Chirp Spread Spectrum.

Very interesting :-)

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

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?

the quick brown fox jumps over the lazy dog

merry xmas to you too!

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.

Decode worked after about 20 tries.

super nice video :)

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

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

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.

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?

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.

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.

64QAM is actually really slow for WiFi and LTE/5G. WiFi 5 and LTE uses 256QAM (8bits) and WiFi 6 and 5G can go up to 1024QAM (10bits). And WiFi 7 will supposedly do 4096QAM (12bits). But obviously the FEC and ARQ at those rates are really high.

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?

That's badass 😱

pinter banget bapake

What are the uses for this acoustic signal communication? How far can you communicate with it (with common equipment)? (I'm quite a foreigner to the world of ham radio)

I would like to learn more about time multiplexing like dmr it uses where 2 stations can transmit at the same time on the same frequency

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)

the best thing about this protocol is the inclusion of emojis! we need emoji Q codes for morse code too. QLOL

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

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?

Hallo, gibt´s eine Handreichung zum Einrichten der App. Klar es gibt nicht viel was man Einrichten kann aber doch genug um aneinander vorbei zu Arbeiten. Sorry die Anfrage ist Deutsch verfasst aber sollte kein Problem sein denke ich.