SDRTrunk - 2 or 3 dongles?

[astankevitz]

Newbee here. I've been searching through the various forum threads using the SDRTrunk software and I haven't been able to get a clear understanding here. Our local EMS has a simulcast control frequency of 857.9875. The other frequencies on this net are: 852.4625, 853.4625, 856.2625, 858.7125 and 859.4325. The span of all these frequencies are greater than 7MHz. If the one dongle is on the control frequency of 857.9875 will the second dongle handle the other frequencies which range over 7 Mhz? (Assuming cheap dongles of 2.4MHz bandwidth.)

I also read on a forum post about setting up dummy frequencies for each dongle to cover the bandwidth but in my case that would exceed the maximum of these dongles.

I also have an SDRplay RSPdx but prefer not to use it as I would like to dedicate a laptop for SDRTrunk only. I use the SDRPlay for other stuff.

Thanks for any help

 

[AM909]

I think you only get about 1.92 MHz (?) usable bandwidth out of the 2.4 MSPS – they start rolling off about 240 kHz in from the edges and that may be taken into account by some software (I don't remember which). So, assuming you need to be able to catch all channels simultaneously, dongle #1 can do 859.4325, 858.7125, and 857.9875 (the CC). Dongle #2 can do 856.2625 only. Dongle #3 can do the remaining 853.4625 and 852.4625. For better balance of resources, you could put the 857.9875 CC on dongle 2.

 

[lwvmobile]

If the system is super busy, then you'll need enough dongles to cover the entire thing. If its not operating at 100% capacity non stop, you might get away with only having 2 dongles and occassionally only miss a call here or there.

 

[astankevitz]

Thanks for the replies. I'm beginning to understand how this works with SDR's and it seems to me that the number of SDRs is related to the amount of traffic and not so much frequency coverage of each dongle. Having one SDR for the control and the second to move about the frequencies seems adequate as long as the trunked network is not super busy. Correct me if I am wrong and thanks again for the help from a newbie.

 

[maus92]

Thanks for the replies. I'm beginning to understand how this works with SDR's and it seems to me that the number of SDRs is related to the amount of traffic and not so much frequency coverage of each dongle. Having one SDR for the control and the second to move about the frequencies seems adequate as long as the trunked network is not super busy. Correct me if I am wrong and thanks again for the help from a newbie.

This is essentially correct.

 

[Pezking]

Use a sdr with higher bandwidth, like the airspy. They have 10mhz usable bandwidth, so they’ll cover everything.

 

[maus92]

Just make sure your machine has the specs to run it.