How do I figure out how many SDR dongles do I need?

[revtex]

Hey All!

I'm very new to SDR and looking for some insight. I have been doing a lot of reading and I'm kind of hung up on how many SDR dongles do I really need? Alot of people point at http://garvas.org/trunk-recorder/ to help figure this out but it looks like that site is now dead. I'm looking to monitor this P25 trunk (Ohio MARCS-IP: Multi-Agency Radio Communications Site: Lake County). Range is 852.575 - 860.8625c. Hardware I'm using is an AirSpy Mini. Any help would be greatly appreciated.

 

[dave3825]

What software would you be using? Overall, you need enough to cover 8.25Mhz

 

[merlin]

Usually two dongles is plenty if you are using tracking/logging software like SDR Trunk.
I use one RTL-SDR with my not so different system and two sites.
I use DSD+Fastlane. It will show all your neighbor sites and control channels.

 

[merlin]

What software would you be using? Overall, you need enough to cover 8.25Mhz



View attachment 151494

Hmmm Why. You are parked on a control channel, and that selects the voice/data channel.

 

[GTR8000]

Hmmm Why. You are parked on a control channel, and that selects the voice/data channel.

Well, no, not if using SDRTrunk. You would need enough to cover as much spectrum is active at any given time in order not to miss any transmissions. SDRTrunk never leaves the control channel to tune to traffic channels, so depending on how busy a particular site is, you might need to cover the entire frequency spread. That can mean maybe just one 10 MHz bandwidth SDRPlay or Airspy R2, or two 6 MHz Airspy Minis, or multiple 2.4 MHz RTL dongles.

 

[revtex]

What software would you be using? Overall, you need enough to cover 8.25Mhz



View attachment 151494

Right now I use SDRTrunk. I was thinking of switching over to trunk-recorder. So I would need to pick up another Airspy Mini to cover that range. Thank you very much!

 

[jtwalker]

Right now I use SDRTrunk. I was thinking of switching over to trunk-recorder. So I would need to pick up another Airspy Mini to cover that range. Thank you very much!

Trunk Recorder (if I am thinking of the right name) is used WITH some other software like SDRtrunk. TR doesn’t communicate with the dongles it just scoops up what SDRtrunk puts out and catalogs it.

 

[dave3825]

Trunk Recorder (if I am thinking of the right name) is used WITH some other software like SDRtrunk. TR doesn’t communicate with the dongles it just scoops up what SDRtrunk puts out and catalogs it.

Two different animals. Trunk Recorder uses dongles and records what it sees. Trunking Recorder retrieves audio from SDRTrunk, Unitrunker and Proscan..

 

[jtwalker]

Two different animals. Trunk Recorder uses dongles and records what it sees. Trunking Recorder retrieves audio from SDRTrunk, Unitrunker and Proscan..

I knew there were two named close. Thanks for correcting me.

 

[dave3825]

knew there were two named close.

And causing issues

 

[jtwalker]

And causing issues



View attachment 151520

Well at least I am not alone in my confusion

 

[merlin]

Well, no, not if using SDRTrunk. You would need enough to cover as much spectrum is active at any given time in order not to miss any transmissions. SDRTrunk never leaves the control channel to tune to traffic channels, so depending on how busy a particular site is, you might need to cover the entire frequency spread. That can mean maybe just one 10 MHz bandwidth SDRPlay or Airspy R2, or two 6 MHz Airspy Minis, or multiple 2.4 MHz RTL dongles.

OK, I didn't know that about SDRTrunk. I think the window for RTL is only two Mhz.

 

[dave3825]

Rtl dongles claim 2.4 usable but but I believe you loose a small amount due to rolloff on the edges.

 

[GTR8000]

The RTL dongles can be stretched to 2.56 MHz if you have a very strong signal from a nearby transmitter site. Even with the fading at the edges, as long as you can keep the noise floor relatively low in relation to the signal, you can usually get away with it.

Or just buy an SDRPlay RSP1a, set it to 10 MHz, and call it a day. The latest releases of SDRTrunk are very good with the SDRPlay devices, I'm running one myself decoding 6 distinct control channels in the 769-775 spectrum, at times decoding upwards of two dozen P25 TDMA transmissions simultaneously.