There are only specific (IMHO-high dollar) radios that can properly decode the multicast trunking systems. Can an SDR radio play these systems? I know SDR has it's advantages and disadvantages like every thing else in this world. I guess this is more a matter of having the proper software since an SDR dongle is in fact a digital device to begin with and can receive PSK QPSK QAM all that, but can it reject multiple streams and know which is the proper one? I know early (samsung) HDTV TV digital converters had same problem. Once they got a firmware update it corrected multipath problems and can reject something like 5 time delayed multipath signals and still choose the right one.
SDR and multi-Cast (multipath)
- Thread starter KR8MR
- Start date
Yes, but in my experience not as well as a Uniden SDS scanner or a Unication G pager.
Maybe getting SDR-trunk requires more tweaking to get things perfect and I just haven’t put in the time.
Maybe getting SDR-trunk requires more tweaking to get things perfect and I just haven’t put in the time.
Multicast trunking systems should be adequately handled by non simulcast optimized receivers like Uniden 436 / 325 as they transmit on a specific frequency from only one tower site. Simulcast trunking systems are a different matter as they transmit on a specific frequency from multiple subsites at the same time, requiring the receiver to process signalling arriving from multiple sites at slightly different timing.
boatbod
Member
Incorrect on both points.
SDR software can do whatever you want it to, subject to the limits of processing power and receive signal strength.
There is at least one sdr app that have been decoding cqpsk and handling P25 multipath since 2013, way before the Uniden SDS or Unication G4/G5 pagers were even designed. Just because someone's experiences are mainly with the highly popular SDR Trunk doesn't make it the only package out there
I use the air spy on a couple P25 TDMA simulcast systems with no issues. I have used the cheaper RTL by noolec with decent results as well. SDR Trunk works very well.
ChrisABQ
...
SDR Trunk is the best.
Advantages:
1. No simulcast issues
2. Can be mobile when used with phone
3. Can decode many channels at once and listen to everything using Trunking Recorder software along with history of every single recorded call (SDS100 & G4 or 5) can only decode one at a time.
4. Far cheaper dongles than a $700 radio
5. Constant updates by creators while scanners will see updates maybe once a year.
6. SDRT is now able to decode control channels for phase 2 TDMA control channels
Feel free to add to this list...
Disadvantages: ??? I personally don't have any.
I'm not hating on SDS100 or G4 or G5, but scanners/pagers can only decode one transmission at a time, then it's gone.
I've now used SDR Trunk for 3 years and I personally will never go back to a handheld radio. Just a fact. I'm in a non distortion simulcast area and my BCD996P2 and BCD436HP are just collecting dust.
Advantages:
1. No simulcast issues
2. Can be mobile when used with phone
3. Can decode many channels at once and listen to everything using Trunking Recorder software along with history of every single recorded call (SDS100 & G4 or 5) can only decode one at a time.
4. Far cheaper dongles than a $700 radio
5. Constant updates by creators while scanners will see updates maybe once a year.
6. SDRT is now able to decode control channels for phase 2 TDMA control channels
Feel free to add to this list...
Disadvantages: ??? I personally don't have any.
I'm not hating on SDS100 or G4 or G5, but scanners/pagers can only decode one transmission at a time, then it's gone.
I've now used SDR Trunk for 3 years and I personally will never go back to a handheld radio. Just a fact. I'm in a non distortion simulcast area and my BCD996P2 and BCD436HP are just collecting dust.
Nothing “incorrect” about what I said, as I worded it as “in my experience”.
This year there've only been 2 sdrtrunk release updates, one in February and one 5 days ago. Far from "constant" imho...
- Joined
- Mar 17, 2020
- Messages
- 976
There's been quite a few commits this year and those updates are accessible with the "nightly" builds. (Which, I've found quite stable overall)
I've tried several of the nightly builds and only found one that was buggy and unstable. If I remember correctly, there was a release that took care of the issue within a day or so. That was back in April. The version that was released yesterday seems to be a good one, and is my favorite so far.
- Joined
- Dec 19, 2002
- Messages
- 2,381
I use an Airspy and DSD+ and have an SDS200. The Airspy with DSD+ (Fast Lane)appears to work as well as the SDS200 on the multicast systems that I monitor using the same antenna. In fact, sometimes I think it actually works better.
I would expect the DSD+FL would work adequately while monitoring a multicast system. The SDS100 doesn't offer any advantage when monitoring a multicast system in terms of decoded audio quality over DSD+FL or other non-simulcast optimized scanners. Things change when monitoring simulcast systems. The SDS100 produces better quality audio when monitoring simulcast systems than DSD+FL or non-optimized receivers. If you want to monitor a simulcast system with software and SDR(s), I recommend either Boatbod OP25 (if you're into Linux) or my current favorite SDRTrunk. I find the audio produced by these two solutions as superior to DSD+FL when monitoring simulcast systems; when monitoring a multicast system (or an ASR) I would expect that all the SDR packages are more or less equivalent in audio quality.
boatbod
Member
Continuous Quadrature Phase Shift Keying
Then there's H-DQPSK, which is Harmonized Differential Quadrature Phase Shift Keying used in P25 Phase 2
I would love to see the vector phasor diagrams aka "constellations" for either of those. I understand some modes like QPSK and QAM and even the basic BPSK that we use in amateur radio to get more mileage using a very narrowband signal. Are you one of those who use a SDR? I cant wait to begin doing that again as soon as we get settled. [possesion of new home is near end of November] I will check out your other posts.
boatbod
Member
Here is a constellation diagram of a nice "clean" decode from a P25 control channel.
This constellation is the same control channel, but affected by adjacent-channel interference because the IF filter was too wide.
