DSDPlus A very serious question.
- Thread starter KMG54
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BTW, it's not only the dongle that determines the quality of simulcast reception - it's the software and $500+ computer that runs it. Then again, my SDS200 has no problem with P25 simulcast. Low end "$300" computers are essentially a commodity item, whereas the $700 SDS200 is essentially a special purpose computer specifically designed to decode P25 simulcast radio systems. And while the ($350 used) midrange notebook PC in my vehicle can (and does occasionally) run SDR software like DSD+, the SDS200 is far more flexible particularly when using a GPS, and does a better job overall.
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All of them. I live in a heavy simulcast area and no problems with a 20 year old PC and dsd+Fastlane. mt 436 stutters along with my TRX1, the dongle on a ancient machine works great.
Neither of those is a $700 scanner, and neither of those was designed to handle simulcast. The "$700 scanner" does just fine on simulcast, because under the hood it's an SDR and a computer.
But what is your point? Yes, you can buy a $20 SDR and a Raspberry Pi (which is $35 for the board, but add in the SD card, power supply, case, etc.) and run OP25 and it works great. But you can't pick that up and take it for a walk, or install it in your truck. And it takes at least some Linux knowledge to get it running. Similar is true with an SDR connected to a PC running DSD+. You need some level of skill to set it up, and it's not as portable as a scanner.
So the answer to your question is: "A computer (even if small or old or both) connected to an SDR can handle simulcast better than a scanner that is built on a traditional receiver design".
boatbod
Member
To the OP:-
Properly receiving a LSM modulated signal requires a DQPSK demodulator which runs from an I-Q sample stream. You can use a C4FM demodulator and recover the same signal (under ideal circumstances) with a more conventional FM demodulator but its performance drops off rapidly when you start introducing phase errors caused by multipath distortion. Subscriber radios, devices like the SDS-200, Unication G4/G5 and SDR software are properly doing DQPSK demod, while lesser scanners do not.
Properly receiving a LSM modulated signal requires a DQPSK demodulator which runs from an I-Q sample stream. You can use a C4FM demodulator and recover the same signal (under ideal circumstances) with a more conventional FM demodulator but its performance drops off rapidly when you start introducing phase errors caused by multipath distortion. Subscriber radios, devices like the SDS-200, Unication G4/G5 and SDR software are properly doing DQPSK demod, while lesser scanners do not.
You can't? I do. I have a pi3b+ installed in my truck running op25 and route the audio thru my stereo's line in. Even stuck it in a backpack with a battery and walked around NYC a few times before sticking it in the truck.
To the op I played with the p25 settings a bit and my 436 does not really stutter any more but everyone's situation will vary.
I want to see photos of the truck installation; I can imagine the backpack portable version.
"Anything's possible ... I taught my dog to say 'I love you'." (Hopefully you'll get the reference.)
Perhaps I should have said "difficult". The average person who wants to listen to their local emergency responders won't do that. Nor will I, even though I'm sitting here looking at a Raspberry Pi with a touchscreen display that's running OP25. For starters, Linux systems don't like being powered off without being shut down first. If yours works great I'm happy for you, but for most people that's not a practical alternative to a scanner. But I'd love to see pictrures too!
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I had op25 running on various flavors of rpi3 and rpi4, but tbh the quirks of the audio subsystem and cable management turned me off. They can work well to feed a stream, but listening to local audio was a bit fussy - and the nest of cables? - yuk. I find an old Intel NUC to work really well with op25 decoding P25P2 simulcast with both local audio and streaming - as long as I don't use an Airspy as the radio. One or two RTL dongles are much more efficient. But a purpose made radio like the SDS200 is a much more flexible solution for my purposes,
boatbod
Member
For someone on the road as much as you I would totally agree!
MTS2000des
5B2_BEE00 Czar
Yup, and an SDS doesn't require hours of setup, software configuration, or hassle. It's "plug and play" and performance is equal to the combo of SDR dongle + software + PC/Pi/whatever. No monitor, keyboard, mouse, HDMI cables, or anything else needed to make it work.
boatbod
Member
Yup, but you do pay $500 more for the convenience
If you spend hours setting it up you did not read the instructions in the notes file. For a dongle, you download Zadig and run i, then DSD, if you get the fastlane package, just unzip it to your DSD folder, then just one small .lib file that a link is supplied for in the notes again added to your DSD folder. You are all set to go. Going to try OP25 when I put enough left over parts together to build another Linux box. Current one is devoted to work.
Exactly my point, your list just came close to $100 !
If you want a display and speakers it ends up being about $200, actually. In that configuration it works as a standalone scanner, no need to run a browser on another device or stream the audio anywhere. I know because I've built several of them.
But again, your original post said: " My question is why does a $20 dollar dongle have no problem with sinulcast on a 300 dollar computer, but a $700 dollar scanner does? "
The $700 scanner DOESN'T have problems with simulcast. The $500 or $400 scanners DO ... in most locations, with most systems.
So yes, an SDR (or two) with either a Pi or a PC is a viable option for people who have the skills and desire to go that direction. But there are lots of folks who don't fit into that category, either because they don't have that level of computer skills or because they want an out-of-the box solution.
I think OP25 is *awesome*, and truly appreciate all the work that boatbod and max have put into making it all that it is. But I also like to be able to download from Radioreference, do remote control with Proscan, easily share programming with other scanners (via drag-and-drop, not vi!), and have a self-contained device I can pick up with one hand and carry around with me, so I have an SDS100 too. More expensive? You bet. But worth it *to me*? Yes.
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