Ribbit/Rattlegram on GMRS

[Blaise]

2 minutes ago, UncleYoda said:

In any case, frequency of a radio transmission does not equate to sound wave frequency

Yes.  That's the point.  We're talking about the sound frequency, not the radio wavelength.  You can't have an "ultrasonic" radio frequency, because "sonic" means sound, not EMF.

[Sshannon]

3 minutes ago, UncleYoda said:

Huh?  20.1 KHz on a Baofeng - what model RX's that?  (I have no idea what a Talkpod is, and probably don't care.)  In any case, frequency of a radio transmission does not equate to sound wave frequency (as I said in my comment above).  An RF signal has to converted to sound by a radio for us to hear it; otherwise, we'd hear constant noise or static coming through the air, like a radio with open squelch.

I'm not sure that I, or you for that matter, know what you are trying to do.  Are you producing a tone on the Talkpod and having a Baofeng "hear it" with the PTT pressed down.?  If nothing else, that would at least result in an open carrier even if the tone isn't hearable.

UncleYoda,

Ribbit is an application that sends text messages between two smart devices using two way radios.  The smart devices emit an audio tone that’s picked up by the radio’s microphone.  A burst of white noise is emitted first to activate squelch at the other end, but at the sending end the person pushes the PTT.

At the receiver end the radio speaker reproduces the sound for the smart device to translate into the text message.  No cables  or modems are involved.  

A Talkpod is a just another brand of two way radio.

 

[UncleYoda]

OK, thanks.  But transmitting an inaudible tone is still using the transmit frequency the radio is set to.  I wonder if that would be considered a form of encryption.  And what about the ID requirement?  I don't think an inaudible ID would suffice.   It seems to me to be an inappropriate use of the normal voice bands, but maybe it would be OK on a designated frequency like they do with 144.390 in HAM.  I don't think there is anywhere in the limited GMRS frequencies where that would be appropriate.  Even audible scrambling would be better and that is mostly not allowed either.

[Sshannon]

17 minutes ago, Blaise said:

I did not.  I set both apps to 20100 Hz, set them next to radios a couple of dozen feet apart, pushed the PTT, and clicked send, and confirmed reception.  I simply took the app's word for it.  In fairness, I could only hear a little crackling, not the usual data-burst, so I'm *pretty* sure it was ultrasonic, but otherwise, I did not have a proper experiment set up, so I can't truly confirm anything...

 

I’m not questioning you, please don’t take it as a personal attack.  We see too much of that.

Here’s why I’m questioning what really happened. Because we use FM the frequency of the RF signal varies with the frequency of the audio which modulates it.  But the government (and courtesy) stipulate how much bandwidth we’re allowed. For FM stereo broadcast transmitters are allowed a wide bandwidth so they can broadcast a wider audio spectrum.  But two way radios is only expected to reproduce speech. In fact I would expect our radios to have a filter between the microphone and the modulator to avoid creating too wide of a bandwidth.  I would also expect that neither the speakers nor microphones on the inexpensive radios to be able to reproduce ultrasound.

I thought I read in their PDFs, that Ribbit attempts to send digital data by converting data into audio tones that are in the center of the spoken voice audio spectrum, between 500 Hz and 2500 Hz. Their centerpoint is 1500 Hz and they go 1000 Hz either side.  20,100 Hz is way above that, but 2100 Hz is right in there.  If you were able to transmit at 20100 Hz, I would be interested in what an RF spectrum analyzer would measure.

But, I always say you can’t argue with empirical evidence, so I’m trying to understand what really happened. 

[UncleYoda]

42 minutes ago, Blaise said:

I did not.  I set both apps to 20100 Hz, set them next to radios a couple of dozen feet apart, pushed the PTT, and clickee ribbit devid send, and confirmed reception.  I simply took the app's word for it.  In fairness, I could only hear a little crackling, not the usual data-burst, so I'm *pretty* sure it was ultrasonic, but otherwise, I did not have a proper experiment set up, so I can't truly confirm anything...

 

With only a couple of dozen feet separation, how do you know the ribbit devices (phones?) did not communicate directly without going through the radios?

[Blaise]

3 minutes ago, Sshannon said:

I’m not questioning you, please don’t take it as a personal attack.

I didn't think you were.  I freely admit that I barely know what I'm doing, and that my methodologies are questionable.
 

4 minutes ago, Sshannon said:

In fact I would expect our radios to have a filter between the microphone and the modulator to avoid creating too wide of a bandwidth.  I would also expect that neither the speakers nor microphones on the inexpensive radios to be able to reproduce ultrasound.

It's certainly possible I tested it wrong. putting a radio down a flight of stairs and in a room across the hall is hardly a variable-isolated testing environment.  Maybe the phone picked up the sound directly, or maybe the app wasn't really transmitting at 20kHz.  I just tried some shit, and it worked, so I based my opinion on that observation without really analyzing it!

8 minutes ago, Sshannon said:

I thought I read in their PDFs, that Ribbit attempts to send digital data by converting data into audio tones that are in the center of the spoken voice audio spectrum, between 500 Hz and 2500 Hz.

If you load the app, there's a menu option for "Danger Zone".  If you go in there, you can turn on ultrasonic transmission.  If you then pick a high sample rate (up to 48kHz), you see lots more frequencies in the Carrier Frequency list, as high as 23,200 Hz.  Now, I have no way of validating that these numbers are *true*.  All I have to go on is that it *said* it was 20100 Hz. When I didn't hear the data burst, but a message arrived, I just assumed it was true!

[Blaise]

4 minutes ago, UncleYoda said:

With only a couple of dozen feet separation, how do you know the ribbit devices (phones?) did not communicate directly without going through the radios?

Well as I said, I don't.  I can't hear my phone *ring* at that range with the ring volume on max, so it seemed reasonable to assume that the speakers can't reach that far.  It's certainly possible that the ultrasonic frequencies penetrate farther through my house, I suppose.  With a dog, a wife, and two rugrats constantly thundering through my environment, opportunities to test are few and far between, so I haven't had the opportunity to implement more variable-controlled experiments yet!

Although, if this app can actually send data 20+ feet through doors and down stairs in your home just using your phone speakers, that would be pretty amazing in and of itself!

[Sshannon]

9 minutes ago, Blaise said:

If you load the app, there's a menu option for "Danger Zone".  If you go in there, you can turn on ultrasonic transmission.  If you then pick a high sample rate (up to 48kHz), you see lots more frequencies in the Carrier Frequency list, as high as 23,200 Hz.  Now, I have no way of validating that these numbers are *true*.  All I have to go on is that it *said* it was 20100 Hz. When I didn't hear the data burst, but a message arrived, I just assumed it was true!

Fascinating.  I haven’t loaded the app yet.  My iPad says it’s too old and I don’t load test apps on my iPhone usually.  I probably need to pick up a couple inexpensive Android tablets to play radio.

[Blaise]

1 hour ago, Sshannon said:

I probably need to pick up a couple inexpensive Android tablets to play radio.

Just grab some old phones on ebay/craigslist.  Much cheaper and easier to store/move/organize...

[Sshannon]

9 minutes ago, Blaise said:

Just grab some old phones on ebay/craigslist.  Much cheaper and easier to store/move/organize...

Yeah, but I’ve kinda been wanting to pick up an Android tablet for ham radio anyway.

[Sshannon]

@Blaise,

So, I finally installed Rattlegram. Everything you said is exactly what they represent. I don’t understand how the speakers and microphones in smartphones can transduce ultrasound, much less the speakers and microphone in a two way radio. I also don’t understand how the radios modulate signals in the ultrasonic range. 
I’m intrigued. 

[Guest]

8 hours ago, Sshannon said:

@Blaise,

So, I finally installed Rattlegram. Everything you said is exactly what they represent. I don’t understand how the speakers and microphones in smartphones can transduce ultrasound, much less the speakers and microphone in a two way radio. I also don’t understand how the radios modulate signals in the ultrasonic range. 
I’m intrigued. 

 

I would not be surprised to learn that modern phones can produce high frequency tones - in fact, we do remember how our students used frequencies above the teachers' hearing threshold to annoy peers without being detected by "old" teachers' ears.

However, I doubt that the radios we use, equipped with microphones and speakers tuned towards voice only, can reach those frequencies.

I own some professional microphones from Beyer Dynamics, Sennheiser, Shure, ... and the one thing that those have in common that their frequency response drops dramatically as frequencies move toward the upper edge of the "young" human hearing experience (20k).

I am still not convinced that "air gapped" audio is the best way to connect a texting encoder and a transmitting device / respectively, a receiver and a texting decoder...

 

 

Edited September 26, 2023 by WRXD372
typos

[Sshannon]

17 minutes ago, WRXD372 said:

I am still not convinced that "air gapped" audio is the best way to connect a texting encoder and a transmitting device / respectively, a receiver and a texting decoder...

 

I don’t think anyone would argue that it’s the best, with all the other devices that are available, but the fact that it doesn’t rely on special hardware or cables makes it potentially valuable in the absence of those devices. 

[flashover52]

I don’t think anyone would argue that it’s the best, with all the other devices that are available, but the fact that it doesn’t rely on special hardware or cables makes it potentially valuable in the absence of those devices. 

Yup, not gonna be the first means for someone but it’s great tech to have. I have been on emergency calls with folks that have disabilities; deaf/blind. For those that are deaf, we often grab a phone or notepad.

In a disaster, this gives someone who can’t hear another option if traditional comm paths are down. Cool stuff!

[WSAL834]

On 9/22/2023 at 10:06 AM, Blaise said:

Compared to the DMR crap regularly blotting out GMRS channels for hours at a time, I would think that a few 1-second bursts per minute at ultrasonic frequencies would be a trivial concern!

DMR on GMRS? I hadn't heard that this was a problem.

[Blaise]

28 minutes ago, WSAL834 said:

DMR on GMRS? I hadn't heard that this was a problem.

I can only speak from my own experience, but around here, there's usually a data buzz blotting at least one GMRS channel for a number of hours several times a week.  Everyone I've asked says it sounds like DMR...