OP25 op25 boatbod

[jbunda83]

This question is for boatbod kinda. I was wondering how op25 is able to scan p25 trunking with 1 sdr and programs like sdrtrunk need 2? Also I ordered 2 sdr dongles with the fc0012 tuner and op25 boadbod is able to use the sub par sdr dongle and scan my local emergency services. The better tuners do work better but it amazes me how much better op25 boatbod is.

 

[maus92]

DSD Fastlane (and now possibly the standard version) can also track a trunking system with only one sdr dongle. In P25 systems, the control channels does the heavy lifting, but there is also a data sub-channel within the voice/traffic channel streams that allow programs like op25 and DSD FL to follow channel grants.

 

[saioke]

This question is for boatbod kinda. I was wondering how op25 is able to scan p25 trunking with 1 sdr and programs like sdrtrunk need 2? Also I ordered 2 sdr dongles with the fc0012 tuner and op25 boadbod is able to use the sub par sdr dongle and scan my local emergency services. The better tuners do work better but it amazes me how much better op25 boatbod is.

That's just the way they're designed. Programs like SDRTrunk are meant to receive multiple channels at the same time so you never really miss a call, while DSD+ and Boatbod are designed to act like a scanner, only getting one call at a time. You can add a second SDR to DSD+ for better priority call support and I'm sure you can do the same for Op25 if you wanted to.

They're all fine choices. I wish I could use SDRTrunk simply because it has better voice quality imo, but for some reason I struggle to pick up the control channel in SDRTrunk even at max gain. So I stick with DSD. I'd say Op25 has better voice quality than DSD too, but DSD is simple to set up for call uploading through rdio-scanner and doing the same through Op25 seems complicated and complex.

 

[boatbod]

Considering this purely from the P25 protocol perspective, all currently active group voice grants and group voice updates are signaled on the control channel and active voice channels. That design ensures that a subscriber radio always knows what is going on and whether they need to temporarily switch tgids to receive a higher priority call or something from their scanlist. The specific messages by which this information is conveyed varies depending whether FDMA or TDMA voice is in progress, but the bulk of the same information is present in either.

OP25 (and presumably also DSD+) use these in-call messages to maintain a complete picture of what is going on across the whole RFSS and can therefore switch around received calls depending on user-defined tgid priority. SDRTrunk uses a different methodology and likes to be configured so that the entire RFSS spectrum is captured through one or more concurrent sdr devices so that there is always a decoder listening to the control channel. OP25 multi_rx can do something very similar, but in practice it doesn't net you much benefit other than filling in the short gaps that would otherwise occur during retuning.

 

[sean_]

I used SDRTrunk with a single nooelec SDR dongle and would receive multiple calls simultaneously.

 

[saioke]

I used SDRTrunk with a single nooelec SDR dongle and would receive multiple calls simultaneously.

You can, but not everyone is that fortunate. A lot of P25 systems out there exceed the 2.4mhz bandwidth limit of the cheap SDRs. On other systems and in my case, you might receive voice from one or two other voice channels, while the rest are locked off. A good majority of folks will likely need a second SDR and in some cases, even 3-4 depending on how large the system is and how spread out the frequency spectrum is.

 

[sean_]

Gotcha, thanks for the input.

I suppose an alternative is an SDR that covers wider bandwidth at once, right? Like the SDRPlay rsp1b?

 

[saioke]

Gotcha, thanks for the input.

I suppose an alternative is an SDR that covers wider bandwidth at once, right? Like the SDRPlay rsp1b?

Yup, some expensive SDRs have higher bandwidths but at the same time, a lot of systems also control channels of at least a 100-150mhz difference between it and the voice channels and afaik there's no singular SDR out there that can have a bandwidth that high. Best to just do your own research on what sites you want to monitor and maybe use this calculator to determine how many you'd need without doing the math yourself.

 

[boatbod]

RTLs are about $35/each, whereas the higher bandwidth sdr devices are typically $200 or more. They are better in so many ways, but you can still get good results with really inexpensive hardware.