Question about trunking a system with a wide frequency range

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sjcscanner

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I am trying to trunk a P25 Phase 1 system with frequencies spread out over a fairly large range compared to what I'm used to. I got the system successfully set up in both DSD Plus and OP25, but it's still missing calls because i'm only using two RTL2832U dongles.
So, if i'm understanding this correctly, the cheaper SDR's have a max bandwidth of 2.4 mhz. The system I'm trying to track has a max frequency of 859.9875 and a min frequency of 854.3375, meaning I need to cover 5.65 mhz of bandwidth to track all voice calls. Am I correct in assuming I need a total of 4 dongles to properly track this system (1 control, 3 voice)? Will DSD Plus and/or OP25 support 4 dongles without any troubles? Thanks!
 

nick0909

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OP25 only needs one dongle, it follows all the action with that since it only tunes to one control channel or TG at a time. There is enough data encoded in every frequency that it knows what is going on without remaining on the control channel. If you are still missing calls it is either because the tuning is still a little off (check the graph plots) or you haven't set up TG priorities to jump to the active TGs if they become active (this might only be a boatbod feature?).

If you want to follow the whole trunk system with something like trunk-recorder you could also get something like a hackrf or airspy/airspy mini that has 6-8mhz bandwidth and try that instead of loading up a ton of cheaper SDRs.
 

Unitrunker2

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So, if i'm understanding this correctly, the cheaper SDR's have a max bandwidth of 2.4 mhz.
That's the sample rate - which is not the same as usable bandwidth. Usable bandwidth is usually 80% of the sample rate. 2 Mhz can be safely expected from a Realtek running at 2.4 msps.

a max frequency of 859.9875 and a min frequency of 854.3375, meaning I need to cover 5.65 mhz of bandwidth to track all voice calls. Am I correct in assuming I need a total of 4 dongles to properly track this system (1 control, 3 voice)?
If you want to record all voice traffic on all channels (not just one live call at a time) - you need three Realteks. Note that an Airspy Mini running 6 msps would not cover all channels since the usable bandwidth is only 4.8 Mhz. Otherwise you need a higher bandwidth SDR.

You can have multiple channels on one SDR provided the frequencies fit in the SDR's usable bandwidth.
 

boatbod

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With a single instance of op25 you can only utilize one dongle and receive one tgid at a time, but you can prioritize the tgids to make sure you hear the traffic you really want to hear. Running multiple instances of op25 is certainly a possibility if you want to monitor multiple tgids in parallel.
 

sjcscanner

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I wasn't aware OP25 only required one dongle, or about the talkgroup priority feature. After messing with it for a while it seems to be doing better. I will eventually get a wider bandwidth SDR or a couple more cheap ones to use with trunk recorder. Thanks for the help.
 
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