SDR# Is there a way to simulate a trunking system with an SDR or PC?

[AD8NT]

While OP25 wishes to support this some day it is not currently available in any production code I've seen.
It's great for decoding calls from a system and tracking said system it's not yet going to simulate one.

Keeping in mind if you are going to transmit something like that you have to be doing so within bands you're licensed for and using proper filtering. That being said unfortunately there's not a lot of bandwidth even in amateur spectrum to do much with a simulated trunking system.

 

[900mhz]

depending on where you live, there should be more than ample bandwidth on 33 cm (902-928 MHz).

 

[Outerdog]

Osmocom (Max) OP25 has "fakecc" -- I've never played with it. Max is familiar with it though.

https://git.osmocom.org/op25/tree/op25/gr-op25_repeater/apps/tx?id=478d2cba70e2f07c46ee4d200b32e5a434ed7de4

 

[AD8NT]

True, though even in the USA that is our band only on a secondary basis. Making something like an amateur trunked station more difficult

 

[AM909]

Depending on the trunking scheme you use, bandwidth isn't really an issue. I've seen single-RF-channel LTR trunks. It seems like it should be possible with DMR also? Two-RF-channel trunks should be possible with any other technology. Given the usage pattern I've heard even in the congested LA area (mostly morse IDs and idle bursts), zillions of dollars and watts could be saved if just a few clubs would get together. All trunks busy would happen approximately never on a 5- or 10-channel system and there'd be a lot more empty space for the FCC to take back. :|

 

[KA1RBI]

Are you asking if you can "fake/broadcast" a trunk system by using an SDR?

Short answer, no
Long answer, no

haha - false, and false. OP25 can be configured to broadcast a P25 control channel, and P25 voice channel(s) at the same time, if desired.

If one doesn't have the necessary SDR transmit hardware (HackRF, USRP, or an eligible analog radio), one could also run a TX/RX pair with a UDP connection between the two running OP25 on both sides. In this case there is no additional hardware required (other than the PC).

Max

 

[dmason04]

haha - false, and false. OP25 can be configured to broadcast a P25 control channel, and P25 voice channel(s) at the same time, if desired.

If one doesn't have the necessary SDR transmit hardware (HackRF, USRP, or an eligible analog radio), one could also run a TX/RX pair with a UDP connection between the two running OP25 on both sides. In this case there is no additional hardware required (other than the PC).

Max

Do you know if there is a link somewhere that will show me how to set that up?

 

[KA1RBI]

After cloning the osmocom OP25 repository there is a file in ......./apps/README-example-udp (duplicated below)...........

Probably best to have some prior experience installing and running OP25. You'll need two files , 1) for source audio for the voice channel, an analog audio WAV file rate 8000, mono, signed int16, and 2) trunk control channel data symbols (follow the procedures to generate this).

Max
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Linking OP25 TX and RX December 2020
===================================================================

The OP25 TX application can be configured to transmit one or more
channels directly to one of the RX apps (rx.py or multi_rx.py) in
each case by specifying a device args string of the form
udp : host : port
where host and port are the IP address and UDP port number,
respectively. Typically, the TX is started first followed by
the RX, but they can be started in any order. UDP port 25252 is
used in the examples.

The sample RX script is in runudp.sh, and the sample TX json config
is in cfg-900.json .

To start the TX
cd .../op25/op25-gr_repeater/apps/tx
./multi_tx.py -c ../cfg-900.json

The RX is started with
cd .../op25/op25-gr_repeater/apps
./runudp.sh

There is a 120KHz sized block of spectrum transmitted (SR=120000)
which is treated as complex baseband with each side pretending that
the spectrum is converted to/from the 900 MHz band. On the RX side
any frequency-change requests are ignored; instead, a "center
frequency" is defined. There are two channels (P25 trunk control
channel and P25 voice channel) spaced at 50 KHz separation.

The TX reads two data files that must be created beforehand. To
create the trunk control channel data symbol file, refer to
tx/README-fakecc.txt
An audio file (PCM/ rate 8000 / mono / signed int16) must also be
created - this file will be real-time encoded with the voice codec
and sent on the P25 voice channel. These two files must be defined
in the cfg-900.json file (channel "source" keyword).
[/code]

 

[KA1RBI]

Decided it might be a good idea to actually test this ... and two new issues have been identified:

1) frequency discrepancies between RX and TX config files (a fix has been pushed). Any p25 symbol data files such as p25.out and sym-cc925.dat must be regenerated (after running 'git pull')

2) p25craft seems to not like python3 (or is it vice-versa?). Until this can be fixed the 'generate tsbks', step 1 in the documentation, will need to be run under python2

Max

 

[AM909]

OT:

Depending on the trunking scheme you use, bandwidth isn't really an issue. I've seen single-RF-channel LTR trunks. ...

Apparently, single-channel P25 systems are also possible: "L3Harris VIDA systems are capable of P25 VDOC (Voice and Data on Control)."

 

[GTR8000]

It was possible with Motorola 3600 systems as well with IntelliRepeater sites. One repeater that switched between control and traffic for very low volume fill-in sites. It's a pretty old concept.

 

[mikewazowski]

Don’t forget the old EDACS SCAT sites.

 

[slicerwizard]

Don’t forget the old EDACS SCAT sites.

Do you mind? I'm right in the middle of dinner!