Why Dongle Decodes P25 Better Than Discriminator Scanner?

[clemfm]

What dongle are you using?

A USB3000? DVSI Products USB-3000™

There appears to be a shortage of information about how to use this, or other dongles, with DSD in Linux, or DSD+ In Windows or WINE.

 

[CanesFan95]

I'm using the cheapie RTL-SDR dongles you get on Amazon for like $21.

The simulcast signal looks nothing like the DMR signal. It's very distinctive. You wouldn't want to step on it with bare feet.

I still don't understand. So you mean if a waveform has a sharp pointed pattern, that means it's simulcast? I guess I've never understood how to look at waveforms and tell stuff about it. Where on earth do we learn how to look at waveforms and interpret what they mean?

 

[clemfm]

I'm using the cheapie RTL-SDR dongles you get on Amazon for like $21.

My mistake, I assumed you were using a P25 (etc) decoding dongle, like the USB3000.

 

[slicerwizard]

I still don't understand. So you mean if a waveform has a sharp pointed pattern, that means it's simulcast?

It means the signal is PSK modulated. That usually means simulcast, but P25 Phase II signals are also supposed to use PSK, so it's not an absolute.

If a single trunking zone services a large area, it pretty much has to have multiple simulcast sites. A couple of local (to me) examples; they cover entire large regions with a single set of frequencies:

Peel Region Trunking System, Peel Region, Ontario - Scanner Frequencies

Peel Region Site Details (Peel Region )


York Region Trunking System, York, Ontario - Scanner Frequencies

Site 1 Site Details (York Region )


You don't get portable / indoor coverage over an 18 to 20 mile radius with a single 770 MHz transmitter site.

You can cover areas of that size with VHF if you only require mobile coverage, i.e. no portables or portables are tied to vehicular or beat repeaters.

So you can make educated guesses most of the time.

I guess I've never understood how to look at waveforms and tell stuff about it. Where on earth do we learn how to look at waveforms and interpret what they mean?

Signals from every one of the dozen or so simulcast sites around here look like that and every other (non-simulcast) signal doesn't. Simulcast/PSK signals also sound much different than regular FM signals, so start with that.