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3 Mar 2024
@silvano:the.alRedman IU2KWOI'm going to install inspectrum too17:47:00
@on1arf:c1.uba.beKristoff ON1ARFOther question. Years ago, I wrote this small project to make a pocsag-transmitter: https://github.com/on1arf/pocsag https://github.com/on1arf/gr-pocsag Looking at the OpenRTX firmware today .. am I correct to assume we could build this into OpenRTX quite easily?17:48:12
@on1arf:c1.uba.beKristoff ON1ARF
In reply to @silvano:the.al
I'm going to install inspectrum too

https://www.youtube.com/watch?v=tGff31uGXQU

Just a demo on how to use inspectrum.

As said, it's not the most complex tool there is, but in a workshop, that is actually the reason why it is usefull.

The participants have to do the decoding of a packet them-self, including timing .. It's is probably the best tool there is to let people really understand why the sync-pattern in front of a datapacket is so important

17:52:46
@silvano:the.alRedman IU2KWO
In reply to @on1arf:c1.uba.be

Other question.

Years ago, I wrote this small project to make a pocsag-transmitter:
https://github.com/on1arf/pocsag
https://github.com/on1arf/gr-pocsag

Looking at the OpenRTX firmware today .. am I correct to assume we could build this into OpenRTX quite easily?

I'd say yes. 😃
17:58:32
@nizzo:matrix.orgnizzo IU2KIN I’ve used Universal Radio Hacker in the past, looks like it has the same functionality of in spectrum  18:42:59
@nizzo:matrix.orgnizzo IU2KIN I would love to see POCSAG decoding in OpenRTX! 18:43:14
@nizzo:matrix.orgnizzo IU2KIN For that and APRS we need a queue system that can log received messages and we need to be able to inspect them from the user interface 18:46:36
@m9r0vsol:c1.uba.beMorgan ON4MODPocsag in openrtx would be so cool! :D18:55:52
@on1arf:c1.uba.beKristoff ON1ARF
In reply to @m9r0vsol:c1.uba.be
Pocsag in openrtx would be so cool! :D

yeah.. Nice for your next FOSDEM talk :-)

One thing at the time, but looking at the code, I get the impression that surely the transmit side should not be to difficult.
Receiving POCSAG will probably be a very different thing.

But, I do leave the UI for somebody else.

20:07:35
@m2426:matrix.orgjames joined the room.20:26:24
@on1arf:c1.uba.beKristoff ON1ARF
In reply to @nizzo:matrix.org
I’ve used Universal Radio Hacker in the past, looks like it has the same functionality of in spectrum 

urh is a lot more advanced then inspectrum, and also still maintained, but for looking at the signal in a physical layer I prefer inspectrum.

I still have not found a way to do C4FM demodulation with urh. There is an option to chose "2 bits per symbol" FSK, but that does not seams to work correctly for me.
I did notice last week there is an option to apply a filter to the FM demodulated signal (AFAIK, c4fm requires you to apply a RRC filter after FM demodulation) but I have not found yet how to decribe that filter correctly. So I am still learning too :-)

20:29:47
@on1arf:c1.uba.beKristoff ON1ARFOK .. did some more investigation on the problem of the start of the transmission. First a picture20:41:32
@on1arf:c1.uba.beKristoff ON1ARFimage.png
Download image.png
20:42:12
@on1arf:c1.uba.beKristoff ON1ARFThis is a test I did where I changed the start of the stream with 20 preamble. 1/ up to 383 ms after the start of the transmission, the frequency of the signal is slighty lower. In all the tests I have done, it is always 383 ms20:45:23
@on1arf:c1.uba.beKristoff ON1ARF * This is a test I did where I changed the start of the stream with 20 preamble. 1/ up to 403 ms after the start of the transmission, the frequency of the signal is slighty lower. In all the tests I have done, it is always 383 ms20:46:59
@on1arf:c1.uba.beKristoff ON1ARF * This is a test I did where I changed the start of the stream with 20 preamble. 1/ up to 403 ms after the start of the transmission, the frequency of the signal is slighty lower. In all the tests I have done, it is always 403 ms20:47:04
@on1arf:c1.uba.beKristoff ON1ARFimage.png
Download image.png
20:47:53
@on1arf:c1.uba.beKristoff ON1ARF2/ This is a close-up the signal around the 400 ms mark 20:47:57
@on1arf:c1.uba.beKristoff ON1ARF

Note two things:

  • this is the preamble signal, so is supposted to be a sinewave.
    Before the 400 ms timemark, the signal is far from a sinewave. Actually it looks like only the top-half of the sinewave is signal is visible.
    It seems to hit some kind of "floor"
  • even after the 400 ms, the signal still is not a sinewave. The signal is still hitting a "floor" somewhere
20:50:34
@on1arf:c1.uba.beKristoff ON1ARFSo I think that even after the 400 ms, the signal is still "overdriven" a bit20:51:35
@silvano:the.alRedman IU2KWOThe "floor" after the 400ms may be an overdrive of the HR_C600020:51:44
@silvano:the.alRedman IU2KWOThe half sinewave is something else20:52:03
@on1arf:c1.uba.beKristoff ON1ARFI agree20:52:14
@on1arf:c1.uba.beKristoff ON1ARFOK, I will all put it in a github bugrapport tomorrow 20:52:42
@silvano:the.alRedman IU2KWOTry to apply this change 20:53:17
@silvano:the.alRedman IU2KWOhttps://github.com/OpenRTX/OpenRTX/commit/44dc9239bee5098365389d8f8cbebb902d928bda20:53:21
@on1arf:c1.uba.beKristoff ON1ARFI don't know if you can add raw iq-files in a github bug raport .. if not, I'll drop it on my nextcloud instance so you can download it20:53:37
@on1arf:c1.uba.beKristoff ON1ARF
In reply to @silvano:the.al
https://github.com/OpenRTX/OpenRTX/commit/44dc9239bee5098365389d8f8cbebb902d928bda
ok .. i'll do this tomorrow.
20:55:10
@silvano:the.alRedman IU2KWO
In reply to @on1arf:c1.uba.be
I don't know if you can add raw iq-files in a github bug raport .. if not, I'll drop it on my nextcloud instance so you can download it
You can upload a zip file, in case
20:55:19
@silvano:the.alRedman IU2KWO
In reply to @on1arf:c1.uba.be
ok .. i'll do this tomorrow.
Thanks
20:55:26

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