question about the working frequency

[iddq]

does it work on 144 or 430 band?

[zacmanchester]

It's currently set up for the 435 MHz band. In theory it can work anywhere between 300 MHz and 1 GHz using the CC430 or CC1101 radios from TI

[iddq]

what is type of modulation? eg. afsk 1200 bell 202?

[zacmanchester]

It uses MSK modulation. Because of the fancy signal processing we're doing, we need to use a phase-coherent modulation scheme, so some kind of phase modulation is a good idea.

[sachatholl]

Hi, so which software TNC software did you use on windows (or linux) to decode the messages generated by the rfm22b and your ax25 implementation?

[zacmanchester]

I've used GQRX on Linux and Mac

[sachatholl]

Hi, thank you ( for having replied to my question. Maybe i didn't specify enough, so i apologize for that. GQRX is the sdr radio receiver (like sdrsharp or hdsdr)+RTL Dongle or so.

What i mean is: how to translate the demodulated signal (which is audible as chirps or bleeping dual-tone sounds, once demodulated by the sdr radio receiver like GQRX or SDRSharp or HDSDR) to readable ascii- text?

As a software TNC, i use soundmodem.exe which is an excellent ax.25 decoder for AFSK, BPSK QPSK modulated signals (http://uz7.ho.ua/packetradio.htm). There is also a highspeed variant of soundmodem (hs_soundmodem from the same developper), which can decode GMSK modulated AX.25 signals from up to 2400baud to a maximum of 19200baud.

in this video you can see hs_soundmodem.exe in action. It is the application in the upper right corner of the video: https://www.youtube.com/watch?v=Yzvi9oWcxhQ

Unfortunately both soundmodem apps seems not be able to decode AX.25 1200 baud that are MSK modulated. (Or am I wrong?)

Your sketch "AX25_Modem.ino" compiles and works on my Arduino mega/RFM22B circuit. I see the signal coming from the RFm22B in the waterfall diag of HDSDR and can hear the signal (basically its a noizy chirp, so i think that should be the MSK signal coming from my RFM22B; i know that its coming from my RFm22B and not from a different radio source; i also checked that the audio is rooted to my soundmodem, and checked that the soundmodem can translate "normal" AFSK AX.25 1200baud Signals from another amateur radio transceiver to text).

So my radio receiver/soundmodem setup works for sure, but it can't translate the signals coming from my RFm22B to text.

So my question is: Which software do you use to translate the audible MSK/AX.25 signals emanating from your AX25 encoder to readable Text after having been demodulated by an sdr receiver as audible audio?

I hope i could clarify my question because i am very interested in using it. I find i awesome to have the possibilty to send ax25 message from a cheap RFm22B and get it translated by a "usual" Amateur radio setup.

Cheers and thanx in advance :-)
Sash

[zacmanchester]

Sorry for the misunderstanding in the previous posts. The AX.25 library will transmit AX.25 packets from an RFM22 or 23 modulated as FSK at 1200 baud (not AFSK as is common in the HAM community). These can be decoded with the typical tools by treating the signal as SSB (rather than FM) before passing it off to the decoder. I do this all in GQRX since it includes a 1200 baud AX.25 decoder.

[sachatholl]

Yeeeah, AAaaah!!! okay!! Right now, I have to go to work but , i will test it tonight!!!! Thank you very much! I will write what happened then :-)

[sachatholl]

Still didn't work, I will make a youtube video, in order to show you what I've got. I am not sure, but it seems to me that I have issues with the baud- rate. Because i don't know how the signal should sound, I want to show you how it actually sounds, coming from my circuit. Also, i think, you maybe need a bit more information regarding my circuit and the RFm22b shield used. I will prepare this today. Thank you in advance - Greetz - Sash

[sachatholl]

Hi Zacmanchester,
It took me some time to install a VM with ubuntu Linux and GQRX. I tested GQRX and its AX.25 decoder which is per default an AFSK decoder working at 1200Baud. It works fine. Now, I tried to get decoded the messages of the RFm22b and your firmware. Obviously, it doesn't work because I think that I must setup the ax.25 decoder of gqrx to understand FSK, but I have no idea how to do this. Could you help me to get thru this jungle? I made a little video where I explain the steps I made and show what it does, in order to better explain in details for you to understand my issues.

https://youtu.be/a7ZatVpDbrY

To resume the key issues:

1. I used an Arduino mega2560 clone from DFROBOT
2. My RFM22b is from modtronics (https://modtronicsaustralia.com/shop/rfm22b-s2-rf-transceiver-breakout-board-v2/)

3)this is the code I use. Only interupt pin and Radio_sdn pin updated and reactivated some serial pront messages:
AX25_RFM22B__zackmanchester1.zip

4. My sdr dongel I use, is this one:
   

5. I configured gqrx to USB (not wide fm), Frequency originally from your code should be 437.505MHz. But i get the strongest signal @ 437.9633 MHz probably due to my SDR not being calibrated.

6. Here are the rest of the settings:
   

7. I guess i need to set up the AX.25 decoder used by gqrx in order to understand FSK1200baud

Then I transferred the code to an original Arduino Mega ADK board. Interestingly, the signal that is transmitted sounds differently although it is exactly the same code! Listen to the next video:

https://youtu.be/wYqLKXQpFec

One question I have is, does the signal showed in the video sound like it should be? So if you could help me in order to get it work, would be awesome. In any case, i'll send you my email: tholl@fh-aachen.de

In the hope to hear from you soon, i send you my best regards,
Sacha

[sachatholl]

This is how the signal looks like in my waterfall:

Is this how it should look like? Still not decoded, but i know that the qtmm decoder which is installed by default uses afsk1200baud, so this is probably the wrong decoder (not fsk)

In order to be sure that I am not working with a damaged rfm22b from modtronic, i tried with a second one that I have, and the signal sounds and looks the same. I think this is good news :-)

I realized that i get 2 signals every time: look:

Wich one should it be, the left one or the right one?

Greetz from germany
Sash

[zacmanchester]

Just sent you an email with some ideas

[daffauk]

does it work for RF4463 module using silicon lab si4463 chip?