The capture is from a local repeater in the Ohio MARCS system. I get pretty strong
signals from a few of them, I believe this one in particular was from London, Ohio in
Madison county (the control channel may actually be in there as well). I do know that
RadioReference streams this repeater through a Uniden BC796D digital scanner.
I'd be happy to capture more if it's of any use or upload the files to another
location.
Thanks
--- In op25-dev(a)yahoogroups.com, Matt Robert <matt.robert80@> wrote:
I thought the same thing but then recalled that 000 is not available as a NAC - the
standard defines the value as having the range 0x001-0xFFF.
I think a capture file would be ideal - this is a curly one for sure!
Bob - which system is this coming off?
Cheers,
Matt
________________________________
From: Steve Glass <stevie.glass@>
To: op25-dev(a)yahoogroups.com
Sent: Thursday, 3 May 2012 11:31 AM
Subject: Re: [op25-dev] Re: OP25 GRC - Almost but not quite working
Â
The 64 bit NID consists of the NAC+DUID (the low order 16 bits) and the error correction
bits (the high order 48 bits). Its possible the NAC is zero for a data frame since it has
its own addressing information within the frame itself. That would leave you with just the
DUID and the appropriate BCH code for that value. Its possible (but not very likely) that
this would mean the high order bits would be mostly zeroes.
On 3 May 2012 01:02, rrgsti <bobrich@> wrote:
>Â
>Hi folks,
>
>I'm still tinkering with this but am running into a bit of a wall with regards to
P25 data.
>
>These two lines are dumped to stderr using a call to the dump_cw function that I
added to the code. I'm only dumping the first 30 bytes for brevity:
>
>
>55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe fc
25 ed
>
>55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 5b 10 ba 16 de 2e 82 69 36 3d 98 1f 9b f8
8e c6
>
>
Based on what I've been able to determine so far, the first 48 bits are frame sync,
and they should be fixed at 0x5575f5ff77ff, which is what we see above.
>
>The next 64 bits are supposed to be NID, which includes the DUID.
>
>I could be wrong, but I believe the 02 (which alternates between 02 and 03 in the
lines below) at the 9th byte, is the status bit-pair that is interleaved every 70 bits (9
bytes * 8 bits - 72 bits into the frame). Once removed, that shifts the remaining bits to
the left 2, which still leaves the NID essentially filled with zeroes except for the last
two bits. Immediately after the NID, however, the bits start flying again.
>
>Does this seem normal? I can't really find any annotated hex dumps of a P25
frame to try to line things up, but it seems that the NID should be populated with
something other than zeroes. If you bit shift the 15th bit 2 to the left, we'll get
a parity bit set every now and then (again, unless I'm messing something up), but
nothing else.
>
>I'm completely open to the fact that this could just be a bad signal, but I can
get very clear decodes of the voice if I force the type to LDU1 or LDU2, and I have never
seen anything but all zeroes here (across many minutes of decoded voice data)
>
>Any thoughts?
>
>
>--- In op25-dev(a)yahoogroups.com, "rrgsti" <bobrich@> wrote:
>>
>>
>> Hi Matt!
>>
>> Thanks for the info, it sounds like that is a very possible option. Is there a
way to see the state of the fsk4 demodulator? I did try running with the updated OP25.py
that Balint put out on Saturday (uses _op25.fsk4 instead of the Radio Raush module, and it
doesn't seem to behave any differently.
>>
>> I did find dump_cw in op25_imbe_frame.h and used it to dump frames right before
their duid is read. I don't know if these will be meaningful, but I'll paste them
in here. Moments of silence have the clusters of 0xff's on the right, while portions
where there is audio has more random numbers.
>>
>> I did note that about 9 bytes into this dump there is a byte that keeps flipping
between 2 and 3. Is it possible this is where the DUID is (shifted a bit or two). Each
row starting with 0x55 0x75 is a new frame dumped, I only dump the first 32 bytes or so of
each one.
>>
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 03 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 5b 10 ba 16 de 2e 82 69 36 3d 98 1f 9b
f8 8e c6
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 74 35 56 de 42 7b ac 05 90 af 5a 0e 12
84 81 6b
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 52 0b 37 d6 c5 a6 11 79 56 f5 9b 1a 1e
22 8a 35
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 7e 2d f0 82 d0 4f f8 4d a2 61 34 94 52
a4 f8 ec
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 4e 46 60 ce 5d a8 8b 27 7f 62 78 ab c2
52 ee 0f
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 00 00 00 02 55 75 f5 ff 77 ff 2d 6f ae
e2 78 2e
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 03 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff ff
fc 25 ed
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 45 5e a4 8b 59 7f 74 31 29 f3 ed d2 36
6c fa 30
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 46 33 55 22 52 69 8e 51 5c 01 0b ae 5a
eb 36 8f
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 5b 10 ba 16 de 2e 82 69 36 3d 98 1f 9a
f8 8e c6
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 00 00 00 02 55 75 f5 ff 77 ff 2d 6f ae
e2 78 2e
>> 55 75 f5 ff 77 ff 00 00 02 00 00 00 00 00 01 26 2d 02 0f 68 4f ff ff ff ff ff fe
fc 25 ed
>>
>>
>>
>
>> --- In op25-dev(a)yahoogroups.com, Matt Robert <matt.robert80@> wrote:
>> >
>> > Hi Bob,
>> >
>> > Its more than likely a result of a bad signal. The FSK4 demod tends to
output zeros when it loses sync which is why the DUID is erroneously coming up as 0x00.
>> >
>> > LDU1/2 are the two types of voice frames. LDU1 has signalling data embedded
and LDU2 has encryption sync data embedded.
>> >
>> > The kludge diff posted below will work - but only for valid frames with a
corrupt DUID value.
>> >
>> >
>> > I'm sure the root cause is the FSK4 demod isn't locking properly
and causing a bad DUID value to be outputted. I have seen similar behaviour in other areas
of OP25 - for example I was looking at the IV/MI value (72 bits) on a local P25 system
here. Whenever the demodulator ran out of talent, it would output steams of constant
zeros.
>> >
>> > Ohio MARCS is a Type 2 Smartzone Omnilink System with CAI compatible ASTRO
voice channels - so its essentially P25 compatible. The P25 CAI spec was based on the
ASTRO CAI from the same era, so its essentially the same thing.
>> >
>> > Is the system running any form of simulcasting?ÃÂ
>> >
>> > Cheers,
>> > Matt
>> >
>> > ________________________________
>> > From: rrgsti <bobrich@>
>
>> > To: op25-dev(a)yahoogroups.com
>> > Sent: Thursday, 26 April 2012 10:59 PM
>> > Subject: [op25-dev] Re: OP25 GRC - Almost but not quite working
>> >
>> >
>> > ÃÂ
>> > Quick update from my end.
>> >
>> > It looks like every frame coming out of the fsk4 demodulator (I'm
assuming, still a n00b here) is marked with a 'duid' of 0x0. Consequently, when
data_unit.cc initializes a new data_unit from the frame, it is always creating it as an
HDU (P25 header) type. This then prevents the IMBE decoder from being executed b/c
it's not a voice data unit type (LDU1/LDU2 (no idea what these mean)).
>> >
>> > I figured maybe it has something to do with our system (Ohio MARCS) not
being full P25 compliant and not including metadata of any sort, so I just made the
following change to data_unit.cc and re-ran it:
>> >
>> > --- op25-orig/blocks/src/lib/data_unit.cc 2012-04-24 10:31:29.139694592
-0400
>> > +++ op25/blocks/src/lib/data_unit.cc 2012-04-26 08:12:35.183962129
-0400
>> > @@ -39,7 +39,8 @@
>> > uint8_t duid = extract(frame_body, 60, 64);
>> > switch(duid) {
>> > case 0x0:
>> > - d = data_unit_sptr(new hdu(frame_body));
>> > + //d = data_unit_sptr(new hdu(frame_body));
>> > + d = data_unit_sptr(new ldu1(frame_body));
>> > break;
>> > case 0x3:
>> > d = data_unit_sptr(new tdu(frame_body, false));
>> >
>> > This seemed to sort of work as I now get rather garbled, but intelligible,
audio from the decoder.
>> >
>> > I've uploaded the baseband capture (1Msps) and resulting audio .wav
file that I get at the following URLS:
>> >
>> >
http://s3.amazonaws.com/public-xrp/p25.iq.bz2
>> >
http://s3.amazonaws.com/public-xrp/p25.wav
>> >
>> > Not sure if this is of any use, but it is encouraging to hear voices at
least. :)
>> >
>> > Thanks!
>> >
>> > Bob
>> >
>> > --- In op25-dev(a)yahoogroups.com, Andy Knitt <andyknitt@> wrote:
>> > >
>> > > It looks like imbe_decoder_factory.cc in OP25 defaults to
>> > > 'software_imbe_decoder'. I manually changed the IMBE
environment variable
>> > > to "soft" and confirmed it with printenv, but I'm still
getting a flat line
>> > > at the output of the OP25 block. Any other ideas?
>> > >
>> > > Thanks,
>> > >
>> > > Andy
>> > >
>> > > On Mon, Apr 23, 2012 at 11:47 PM, Balint <balint256@> wrote:
>> > >
>> > > > **
>> > > >
>> > > >
>> > > > I *still* haven't checked out the latest code, but in my old
code the
>> > > > default voice frame output was (null?).****
>> > > >
>> > > > There are options for file output, null, external (hardware)
decoder and
>> > > > internal decoder. You used to be able to spec this on the command
line as
>> > > > an environment variable:****
>> > > >
>> > > > export IMBE=soft****
>> > > >
>> > > > I changed my default to be the internal decoder (see
>> > > > `imbe_decoder_factory.cc').****
>> > > >
>> > > > ** **
>> > > >
>> > > > *From:* op25-dev(a)yahoogroups.com
[mailto:op25-dev@yahoogroups.com] *On
>> > > > Behalf Of *Andy Knitt
>> > > > *Sent:* Tuesday, 24 April 2012 12:45 PM
>> > > > *To:* op25-dev(a)yahoogroups.com
>> > > > *Subject:* [op25-dev] OP25 GRC - Almost but not quite
working****
>> > > >
>> > > > ** **
>> > > >
>> > > > ****
>> > > >
>> > > > I have the OP25 GRC demo that Balint provided up and running.
>> > > > Everything seems to working except I'm not getting any audio
out of
>> > > > the OP25 block. I'm getting the "four line" output
from the dibit
>> > > > output port when there is traffic on the channel, and the
autotune
>> > > > output is outputting data. However, no audio. I put a scope on
the
>> > > > audio output and it's a flat line at zero, even when the
dibit output
>> > > > is "four lines". Any tips on how to further
troubleshoot?
>> > > >
>> > > > Thanks,
>> > > >
>> > > > Andy****
>> > > >
>> > > > ****
>> > > >
>> > > >
>> > > >
>> > >
>> >
>>
>
>